Free Complaint - District Court of Delaware - Delaware

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IN THE UNITED STATES DISTRICT COURT FOR THE DISTRICT OF DELAWARE POWER INTEGRATIONS, INC., a Delaware corporation, Plaintiff,
V.

C.A. No. FAIRCHILD SEMICONDUCTOR INTERNATIONAL, INC., a Delaware corporation, FAIRCHILD SEMICONDUCTOR CORPORATION, a Delaware corporation, and SYSTEM GENERAL CORPORATION, a Taiwanese corporation, Defendants. JURY TRIAL REQUESTED

COMPLAINT FOR PATENT INFRINGEMENT Plaintiff Power Integrations, Inc. hereby alleges as follows:

THE PARTIES 1. Power Integrations, Inc. ("Power Integrations") is incorporated under the laws of

the state of Delaware, and has a regular and established place of business at 5245 Hellyer Avenue, San Jose, California, 95138. 2. Upon information and belief, defendant Fairchild Semiconductor International,

Inc. is incorporated under the laws of the state of Delaware, with its headquarters located at 82 Running Hill Road, South Portland, Maine, 04106. 3. Upon information and belief, defendant Fairchild Semiconductor Corporation is

incorporated under the laws of the state of Delaware, with its headquarters located at 82 Running Hill Road, South Portland, Maine, 04106. 4. Upon information and belief, defendant System General Corporation (hereinafter

"SG") is incorporated under the laws of Taiwan, with its headquarters located at 517, No. 9, Alley

1

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6, Lane 45 Bao Shing Road, Shin Dian, Taipei, Taiwan. Upon information and belief, SG is a wholly owned subsidiary of Fairchild Semiconductor International, Inc. 5. Defendant Fairchild Semiconductor International, Inc., defendant Fairchild

Semiconductor Corporation, and defendant SG will hereinafter be collectively referred to as "Defendants." JURISDICTION AND VENUE 6. This action arises under the patent laws of the United States, Title 35 U.S.C. § 1 et

seq. This Court has subject matter jurisdiction under 28 U.S.C. §§ 1331 and 1338(a). 7. Upon information and belief, this Court has personal jurisdiction over Defendants

because Defendants have purposely availed themselves of the privilege of conducting activities within this State and District. 8. Upon information and belief, venue is proper in this Court pursuant to 28 U.S.C.

§§ 1391(b), 1391(c), and 1400 because Defendants are subject to personal jurisdiction in this judicial District. GENERAL ALLEGATIONS 9. Power Integrations' products include its TOPSwitch®, TinySwitch®,

LinkSwitch®, and DPA-Switch® families of power conversion integrated circuit devices, which are used in power supplies for electronic devices such as cellular telephones, LCD monitors, and computers. These products are sold throughout the United States, including Delaware. 10. Defendants manufacture pulse width modulation ("PWM") controller integrated

circuit devices (e.g., devices intended for use in power conversion applications such as LCD monitor power supplies, off-line power supplies or battery chargers for portable electronics), and directly, and through their affiliates, make, use, import, sell, and offer to sell the same throughout the United States, including Delaware. Defendants also support and encourage others to import, use, offer for sale, and sell throughout the United States, including Delaware, products incorporating Defendants' integrated circuit devices.

2

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FIRST CAUSE OF ACTION INFRINGEMENT OF U.S. PATENT NO . 6,107,851 11. herein. 12. Power Integrations is now, and has been since its issuance, the assignee and sole The allegations of paragraphs 1-10 are incorporated as though fully set forth

owner of all right, title, and interest in United States Patent No. 6,107,851, entitled "Offline Converter with Integrated Softstart and Frequency Jitter" ("the '851 patent"), which was duly and legally issued on August 22, 2000. A true and correct copy of the '851 patent is attached hereto as Exhibit A. 13. Defendants have been and are now infringing, inducing infringement, and

contributing to the infringement of the '851 patent in this District and elsewhere by making, using, selling, offering to sell, and/or importing devices, including PWM integrated circuit devices, covered by one or more claims of the '851 patent, and/or contributing to or inducing the same by third-parties, all to the injury of Power Integrations. 14. 15. Defendants' acts of infringement have injured and damaged Power Integrations. Defendants' acts of infringement have been, and continue to be, willful so as to

warrant the enhancement of damages awarded as a result of their infringement. 16. Defendants' infringement has caused irreparable injury to Power Integrations and

will continue to cause irreparable injury until Defendants are enjoined from further infringement by this Court. SECOND CAUSE OF ACTION INFRINGEMENT OF U.S. PATENT NO. 6,249,876 17. herein. 18. Power Integrations is now, and has been since its issuance, the assignee and sole The allegations of paragraphs 1-10 are incorporated as though fully set forth

owner of all right, title, and interest in United States Patent No. 6,249,876, entitled "Frequency Jittering Control for Varying the Switching Frequency of a Power Supply" ("the '876 patent"), 3

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which was duly and legally issued on June 19, 2001. A true and correct copy of the '876 patent is attached hereto as Exhibit B. 19. Defendants have been and are now infringing, inducing infringement, and

contributing to the infringement of the '876 patent in this District and elsewhere by making, using, selling, offering to sell, and/or importing devices, including PWM integrated circuit devices, covered by one or more claims of the '876 patent, and/or contributing to or inducing the same by third-parties, all to the injury of Power Integrations. 20. 21. Defendants' acts of infringement have injured and damaged Power Integrations. Defendants' acts of infringement have been, and continue to be, willful so as to

warrant the enhancement of damages awarded as a result of their infringement. 22. Defendants' infringement has caused irreparable injury to Power Integrations and

will continue to cause irreparable injury until Defendants are enjoined from further infringement by this Court. THIRD CAUSE OF ACTION INFRINGEMENT OF U.S. PATENT NO. 7,110,270 23. herein. 24. Power Integrations is now, and has been since its issuance, the assignee and sole The allegations of paragraphs 1-10 are incorporated as though fully set forth

owner of all right, title, and interest in United States Patent No. 7,110,270, entitled "Method and Apparatus for Maintaining a Constant Load Current with Line Voltage in a Switch Mode Power Supply" ("the '270 patent"), which was duly and legally issued on September 19, 2006. A true and correct copy of the '270 patent is attached hereto as Exhibit C. 25. Upon information and belief, Defendants have been and are now infringing,

inducing infringement, and contributing to the infringement of the '270 patent in this District and elsewhere by making, using, selling, offering to sell, and/or importing devices, including PWM integrated circuit devices, covered by one or more claims of the '270 patent, and/or contributing to or inducing the same by third-parties, all to the injury of Power Integrations. 4

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26. 27.

Defendants' acts of infringement have injured and damaged Power Integrations. Defendants' infringement has caused irreparable injury to Power Integrations and

will continue to cause irreparable injury until Defendants are enjoined from further infringement by this Court.

PRAYER FOR RELIEF WHEREFORE, Plaintiff requests the following relief: (a) (b) (c) (d) judgment that Defendants infringe of the '851 patent; judgment that Defendants infringe of the '876 patent; judgment that Defendants infringe of the '270 patent; a permanent injunction preventing Defendants and their officers, directors, agents,

servants, employees, attorneys, licensees, successors, assigns, and customers, and those in active concert or participation with any of them, from making, using, offering to sell, or selling in the United States or importing into the United States any devices that infringe any claim of the '851, '876, or '270 patents, or contributing to or inducing the same by others; (e) judgment against Defendants for money damages sufficient to compensate Power

Integrations for Defendants' infringement of the '851, '876, and '270 patents in an amount to be determined at trial; (f) that any such money judgment be trebled as a result of the willful nature of

Defendants' infringement; (g) an accounting for infringing sales not presented at trial and an award by the court

of additional damages for any such infringing sales; (h) costs and reasonable attorneys' fees incurred in connection with this action

pursuant to 35 U.S.C § 285; and (i) such other and further relief as this Court finds just and proper.

5

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JURY DEMAND Plaintiff Power Integrations requests trial by jury.

Dated: May 23, 2008

FISH & RICHARDSON P.C.

By.,
William J. Marsden,\Jr. (#2247) Kyle Wagner-Compton (#4693) 919 N. Market St`r`eet;-Suite 1100 P.O. Box 1114 Wilmington, DE 19801 Telephone: (302) 652-5070 Facsimile: (302) 652-0607 Email: marsden a,fr.com kcompton ,fr.com Frank E. Scherkenbach 225 Franklin Street Boston, MA 02110-2804 Telephone: (617) 542-5070 Facsimile: (617) 542-8906 Howard G. Pollack Michael R. Headley Scott Penner 500 Arguello Street, Suite 500 Redwood City, CA 94063 Telephone: (650) 839-5070 Facsimile: (650) 839-5071 Attorneys for Plaintiff POWER INTEGRATIONS, INC.
80061065.doc

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Exhibit A

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United States Patent
Balakirshnan et al.

[I91

[ill [45]

Patent Number: Date of Patent:

6,107,851
Aug. 22,2000

[54] OFFLINE CONVERTER WITH INTEGRATED SOFTSTART AND FREQUENCY JITTER [75] Inventors: Balu Balakirshnan; Alex Djenguerian, both of Saratoga; Leif Lund, San Jose, all of Calif. [73] Assignee: Power Integrations, Inc., Sunnyvale, Calif. [21] Appl. No.: 091080,774 [22] Filed:

4,887,199 1211989 Whittle ...................................... 363149 4,888,497 1211989 Dallabora et al. ................... 3071272.3 4,890,210 1211989 Myers ....................................... 363121 4,928,220 511990 White ........................................ 363156 4,937,728 611990 Leonardi ................................... 363197

(List continued on next page.) FOREIGN PATENT DOCUMENTS
European European European European European European European European Pat. Pat. Pat. Pat. Pat. Pat. Pat. Pat. Off. Off. Off. Off. Off. Off. Off. Off.

May 18, 1998

[51] Int. CL7 ..................................................... H03K 31017 [52] U.S. C1. ........................... 3271172; 3271531; 3271544 [58] Field of Search ..................................... 3271172, 173, 3271174, 175, 176, 530, 531, 544 ~561

....... H02M 31335 ...... HOlL 231433 ...... HOlL 231495 ......... H02M 1112 ........ H05B 41100 ......... H02M 3100 ....... H02M 31155 ....... H03K 17116

OTHER PUBLICATIONS H.S. Hoffman, Jr., Self-Generated Bias Supply, IBM Technical Disclosure Bulletin, vol. 20, No. 5, Oct. 1997, pp. 1814-1815. (List continued on next page.) Primary Examiner-Je ffrey Zweizig Attorney, Agent, or F i r m 4 l a k e l y , Sokoloff, Taylor & Zafman, LLP

References Cited
U.S. PATENT DOCUMENTS
111970 111971 1011974 1011975 211978 311979 1011980 1111980 111985 1211985 1111986 911987 1111987 1111987 111988 211988 311988 411988 211989 211989 311989 311989 811989 811989 911989 911989 Petrohilos ............................... 3071229 Buchanan et al. ........................ 321143 Aggen et al. ............................... 32112 Daniels et al. .......................... 3071265 Kondo ....................................... 354151 Berard, Jr. et al. ....................... 307143 de Sartre et al. ......................... 363156 Ohsawa et al. ........................... 363149 Simi et al. ................................ 363121 Davidson .................................. 363121 Rodriguez et al. ....................... 363137 Whittle ...................................... 363121 Kettschau .................................. 363121 Josephson ................................. 363124 Faini ........................................ 307118 Cini et al. ............................... 3231283 Barthold .................................... 363116 Farnsworth et al. ...................... 363121 Claydon et al. ........................ 3231311 Barn ........................................ 363120 Koninsky et al. ........................ 363117 Hrassky .................................. 3181254 Barlage ..................................... 363121 Inou et al. ................................ 363121 Odaka et al. ............................. 363149 White ........................................ 363121

[571

ABSTRACT

A pulse width modulated switch comprises a first terminal, a second terminal, and a switch that allows a signal to be transmitted between the first terminal and the second terminal according to a drive signal provided at a control input. The pulse width modulated switch also comprises a frequency variation circuit that provides a frequency variation signal and an oscillator that provides an oscillation signal having a frequency of that varies within a frequency range according to the frequency variation signal. The oscillator further provides a maximum duty cycle signal comprising a first state and a second state. The pulse width modulated switch further comprises a drive circuit that provides the drive signal when the maximum duty cycle signal is in the first state and a magnitude of the oscillation signal is below a variable threshold level.

18 Claims, 9 Drawing Sheets

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6,107,851
Page 2

U.S. PATENT DOCUMENTS
4,943,903 5,012,401 5,014,178 5,034,871 5,041,956 5,072,353 5,086,364 5,146,394 5,161,098 5,177,408 5,200,886 5,297,014 5,313,381 5,394,017 5,452,195 5,461,303 5,481,178 5,508,602 5,528,131 5,552,746 5,563,534 5,568,084 5,570,057 5,572,156 5,617,016 5.619.403 , , 5,621,629 5,640,317 711990 411991 511991 711991 811991 1211991 211992 911992 1111992 111993 411993 311994 511994 211995 911995 1011995 111996 411996 611996 911996 1011996 1011996 1011996 1111996 411997 411997 411997 611997 Cardwell, Jr. ............................. 363197 Barladge ................................... 363197 Balakrishnan ............................ 363149 Okamoto et al. ......................... 363115 Marinus .................................... 363121 Feldkeller ................................. 363120 Leipold et al. ........................... 361118 Ishii et al. ................................. 363116 Balakirshnan .......................... 3631144 Marques .................................. 3151291 Schwartz et al. ......................... 363149 Saito et al. ................................ 363121 Balakrishnan .......................... 3631147 Catano et al. ............................ 307166 Lehr et al. ................................ 363121 Leman et al. ........................... 3231222 Wilcox et al. .......................... 3231287 Borgato et al. ......................... 3231222 Marty et al. ............................ 3231901 Danstrom ................................ 3271427 Rossi et al. ............................... 327177 McClure et al. ........................ 3271538 Palara ...................................... 3271365 Diazzi et al. ........................... 3271109 Borghi et al. ........................... 3231284 Ishikawa et al. ......................... 363121 Hemminger et al. ..................... 363156 Lei ........................................ 363149

OTHER PUBLICATIONS H. S. Hoffman, Jr. et al, Proportional Drive Supply with Diversion Control, IBM Technical Disclosure Bulletin, vol. 21, No. 12, May 1979, pp. 49044905. A. Halperin, 'Primary Regulated Dual Power Supply', IBM Technical Disclosure Bulletin, vol. 21, No. 10, Mar. 1979, pp. 4299-4300. "5-W dc-dc converters aim at telecomm applications", Electronic Design vol. 31, No. 15, Jul. 21, 1983, pp 227. "Combined Switch-Mode Power Amplifier and Supply", IBM Technical Disclosure Bulletin, vol. 28, No. 3, Aug. 1985, pp. 1193-1195. R. Bmckner, et al, "Optimizing Converter Design and Performance Utilizing Micro Controller System Feedback Control", Proceedings of Powercon 8, E-2, 1981, pp 1-10. B. Pelly et al, OPower MOSFETs take the load off switching supply design, Electronic Design, Feb. 1983, pp 135-139. D. Azzis et al, Flyback on Card Power Supply, IBM Technical Disclosure Bulletin, vol. 23, No. 4, Sep. 1980, pp. 1477-1478. A.J. Bowen et al, Power Supply with Optical Isolator, IBM N;. Technical Disclosure ~ulletiXvbl.14, 11,Apr. 1972, pp. 3320. "Off-Line Power Supply Control Technique Using a Single Transformer to Feed Back Three Control Signals", IBM Technical Disclosure Bulletin, vol. 32, No. 8-4, Jan. 1990, pp. 272-273.

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6,107,851

1
OFFLINE CONVERTER WITH INTEGRATED SOFTSTART AND FREQUENCY JITTER

2

up. At start up, the voltage, current and power at the output of the power supply will essentially be zero. The pulse width modulated switch will then conduct for the maximum posBACKGROUND sible amount of time in each cycle of operation. The result 1. Field of the Invention 5 of this is a maximum inrush current into the power supply. The field of the present invention pertains to the field of The maximum inrush current is greater than the current that power supplies and among other things to the regulation of is utilized during normal operation of the power supply. The power supplies. maximum inrush current stresses the components of power 2. Background of the Invention supply and switch. Stress is specifically a problem for the Power supplies that convert an AC mains voltage to a DC lo switch, or transistor, the transformer of the power supply, voltage for use by integrated electronic devices, amongst and the secondary side components of the power supply. The other devices, are known. The power supplies are required stress caused by the maximum inrush current decreases the to maintain the output voltage, current or power within a overall life of the power supply and increases the cost of the power supply because the maximum rating of the comporegulated range for eficient and safe operation of the electronic device. Switches that operate according a pulse width nents used in the power supply to not destruct from the modulated control to maintain the output voltage, current, or inrush currents will be greater than the maximum rating power of the power supply within a regulated range are also required for normal operation. known. These switches utilize an oscillator and related Further, when the pulse width modulated switch conducts circuitry to vary the switching frequency of operation of the for the maximum possible amount of time in each cycle of switch, and therefore regulated the power, current or voltage 20 operation the voltage, current and power at the output of the that is supplied by the power supply. power supply rise rapidly. Since the feedback circuit of the Aproblem with utilizing pulse width modulated switches power supply often does not respond as fast as the operating is that they operate at a relatively high frequency compared frequency of the switch, the rapid rise of the voltage, current to the frequency of the AC mains voltage, which results in and power will often result in an overshoot of the maximum a high frequency signal being generated by the power 25 voltage in the regulation range which will cause damage to supply. This high frequency signal is injected back into the the device being supplied power by the power supply. AC mains input and becomes a component of the AC mains Referring to FIG. 1 a known power supply that attempts signal. The high frequency signals are also radiated by the to minimize EM1 and reduce startup stress is depicted. A power supply as electromagnetic waves. These high frerectifier 10 rectifies the filtered AC mains voltage 5, from quency signals add to the Electromagnetic Interference 30 EM1 filter 120, input by the AC mains to generate a rectified (EMI) of the power supply, and in fact are the largest voltage 15. Power supply capacitor 20 then generates a substantially DC voltage with a ripple component. The contributors to the EM1 of the power supply. The EM1 generated by the power supply can cause problems for rectified voltage 15 with ripple component is provided to the communications devices in the vicinity of the power supply primary winding 35 of transformer 40 that is used to provide and the high frequency signal which becomes a component 35 power to secondary winding 45. The output of secondary of the AC mains signal will be provided to other devices in winding 45 is provided to secondary rectifier 50 and secthe power grid which also causes noise problems for those ondary capacitor 55 that provide a secondary DC voltage 60 devices. Further, the radiated EM1 by the power supply can at the power supply output 65 to the device that is coupled interfere with radio and television transmissions that are to the power supply. transmitted over the air by various entities. In order to maintain the secondary DC voltage within a 40 To combat the problem of EMI, several specifications regulate range a feedback loop including an optocoupler 70, have been developed by the Federal Communications Comzener diode 75 and a feedback resistor 80 provides a signal mission (FCC) in the United States and the European indicative of the voltage at the power supply output 65 to Community (EC) have established specification that specify feedback pin 85 of pulse width modulated switch 90. The the maximum amount of EM1 that can be produced by 45 voltage magnitude at the feedback terminal is utilized to classes of electronic devices. Since power supplies generate vary the duty cycle of a switch coupled between the drain terminal 95 and common terminal 100 of the pulse width a major component of the EM1 for electronic devices, an important step in designing a power supply is minimizing modulated switch 90. By varying the duty cycle of the switch the average current flowing through the primary the EM1 provided by the power supply to levels with the acceptable limits of the various standards. Since, a power 50 winding and therefore the energy stored by the transformer supply can be utilized in many different countries of the 40 which in turn controls the power supplied to the power world, the EM1 produced should be within the most stringent supply output 65 is kept within the regulated range. A limits worldwide to allow for maximum utilization of the compensation circuit 105 is coupled to the feedback pin 85 power supply. in order to lower the bandwidth of the frequency of operaA known way of minimizing the EM1 provided by the 5s tion of the pulse width modulator. power supply is by adding an EM1 filter to the input of the Inrush currents are minimized at start up by use of soft power supply. An EM1 filter generally utilizes at least one start capacitor 110. Soft start functionality is termed to be a inductor, capacitor and resistor in combination. However, functionality that reduces the inrush currents at start up. At the greater EM1 produced by the power supply the larger the this instant a current begins to flow through feedback components that are utilized as part of the EM1 filter. The 60 resistor 80 and thereby into soft start capacitor 110. As the cost of the EM1 filter is in large part determined by the size voltage of soft start capacitor 110 increases slowly, current of the inductor and capacitor utilized. The longer the will flow through light emitting diode 115 of optocoupler 70 components, the higher the cost of the power supply. thereby controlling the duty cycle of the switch. Once the voltage of the soft start capacitor 110 reaches the reverse Further, simply utilizing an EM1 filter does not address the radiated EMI. 65 breakdown voltage of Zener diode 75 current will flow Another problem associated with pulse width modulated through zener diode 75. The approach described above will switches results from operation of the power supply at start reduce the inrush currents into the power supply, however,

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6,107,851

3

4

it will be several cycles before the light emitting diode 115 signal to be transmitted between a first terminal and a second will begin conducting. During the several cycles the maxiterminal according to a drive signal, a drive circuit that mum inrush current will still flow through the primary provides the drive signal and a soft start circuit that provides winding and other secondary side components. During these a signal instructing the drive circuit to disable the drive cycles the transformer may saturate, and therefore the trans- 5 signal. former may have to be designed utilizing a higher core size In yet another embodiment the present invention than would be required for normal operation even with the prises a regulation circuit comprising a switch that allows a use of soft start capacitor as in FIG. 1. signal to be transmitted between a first terminal and a second To reduce the EM1 Output the Power an EM1 terminal according to a drive signal, a frequency variation filter 120 is utilized. Additionally, pulse width modulated 10 that provides a frequency variation signal, and a drive switch 90 is equipped with frequency oscillation terminals that provides a drive signal for a maximum time 125 and 130. Frequency oscillation terminal 125 and 130 period of a tirne duration cycle, ~h~ tirne duration of the receive a jitter current 135 that varies according to the ripple cycle varies according to the frequency variation signal, component of substantially DC voltage 15. The jitter current In the above referenced embodiments the pulse width is used to vary the of the saw-toothed ls modulated switch or regulation circuit may comprise a waveform generated by the oscillator contained in the pulse monolithic device. width modulated switch 90. The saw toothed waveform An object of an aspect of the present invention is directed generated by the oscillator is to the feedback to a pulse width modulated switch that has integrated soft provided at the feedback pin 85, As the frequency of the saw toothed waveform varies, so will the switching frequency of 20 Start capabi1ities. Another object of an aspect of the present invention is the switch coupled between the drain and common terminal. directed toward a pulse width modulated switch that has This allows the switching frequency of the switch to be integrated frequency variation capabilities. spread over a larger bandwidth, which minimizes the peak value of the EM1 generated by the power supply at each Yet another object of an aspect of the present invention is frequency. By reducing the EM1 the ability to comply with 25 directed toward a pulse width modulated switch that has government standards is increased, because the government integrated frequency variation capabilities and integrated standards specify quasi-peak and average values at given soft start capabilities. frequency levels. Varying the frequency of operation of the A further object of an aspect of the present invention is pulse width modulated switch by varying the oscillation directed toward a low cost regulated power supply that has frequency of the oscillator is referred to as frequency jitter. 30 both soft start and frequency variation capabilities, A problem associated with the reduction scheme This and other objects and aspects of the present invendescribed with respect is that the tions are taught, depicted and described in the drawings and will have variances due to variations in the line voltage and the description of the invention contained herein, output load. Additionally, since the ripple may vary, design and the component value of EM1 resistor 140 is difficult to 35 BRIEF DESCRIPTION OF THE DRAWINGS determine and correspondingly design of the power supply FIG. 1 is a known power supply utilizing a pulse width becomes problematic. modulated switch, and external soft start, and frequency SUMMARY OF THE INVENTION jitter functionality. In One the present a 40 FIG. 2 is a presently preferred power supply utilizing an pulse width modulated switch comprising a switch that pulse width modulated switch according to the present allows a signal to be transmitted between a first terminal and invention, a second terminal according to a drive signal. The pulse FIG. 3 is a presently preferred pulse width modulated width modulated switch also comprises a frequency variaswitch according to the present invention. tion circuit that provides a frequency variation signal and an 45 FIG. 4 is a timing diagram of the soft start operation of the oscillator that provides an oscillation signal having a fiepresently preferred pulse width switch quency that varies within a frequency range according to the the present invention. frequency variation signal. The oscillator further provides a FIG. 5 is a timing diagram of the frequency jitter operamaximum duty cycle signal comprising a first state and a tion of the presently preferred pulse width modulated switch second state. The pulse width modulated circuit further according to the present invention. comprises a drive circuit that provides the drive signal when the maximum duty cycle signal is in the first state and a FIG. 6 is an alternate presently preferred pulse width magnitude of the oscillation signal is below a variable modulated switch according to the present invention. threshold level. FIG. 7 is a timing diagram of the operation of the alternate Another anbodiment of the Present invention comprises 55 presently preferred pulse width modulated switch of FIG. 6 a pulse width modulated switch comprising a switch comaccording to the present invention, prising a the switch a be FIG, 8 is a presently preferred power supply utilizing a transmitted between a first terminal and a second terminal regulation circuit according to the present invention, according to a drive signal. The pulse width modulated is a presently preferred regu1ati0n circuit switch also comprises an oscillator that provides a maximum 60 to the present invention. duty cycle signal comprising an on-state and an off-state, a drive circuit that provides the drive signal, and a soft start circuit that provides a signal instructing said drive circuit to disable the drive signal during at least a portion of said on-state of the maximum duty cycle. In an alternate embodiment the present invention comprises a regulation circuit comprising a switch that allows a DESCRIPTION OF THE PREFERRED EMBODIMENT
65

Referring to FIG. 2, EM1 filter 200 is coupled to an AC mains voltage 205. The AC mains voltage 205 is rectified by rectifier 210. The rectified voltage 215 is provided to power

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supply capacitor 220 which provides a substantially DC supply is coupled is switched on, a power up signal is generated within the internal circuitry of pulse width moduvoltage 225. The substantially DC voltage 225 is provided to lated switch 262. The power up signal is used to trigger soft the primary winding 230 of transformer 235 which stores the start circuitry that reduces the duty cycle of the switch that energy provided to the primary winding 230, When the primary winding 230 is no longer receiving energy, energy 5 operates within the pulse width modulated switch 262 for a predetermined period of time, which is presently preferred to is delivered by the transformer 235 to the secondary winding 240. The voltage induced across the secondary winding 240 be ten (lo) Once start is pulse width switch 262 Operates is rectified by rectifier 245 and then transformed into setaccording to its regu1ar duty ondary substantially DC voltage 265 by secondary capacitor Alternatively, or in addition to soft start functionality, 260 and provided to the power supply output 267. lo pulse width modulated switch 262 may also have frequency is longer provided the primary winding 230 jitter functionality, That is, the switching frequency of the when the pulse width modulated switch 262, which is pulse width modulated switch 262 varies according to an the primary winding 230, ceases internal frequency variation signal. This has an advantage Pulse width modulated switch 262 is a switch that is the frequency jitter operation of FIG, 1 in that the controlled by a pulse width modulated signal. Pulse width 1s frequency range of the presently preferred pulse width modulated switch 262 conducts and ceases conduction modulated switch 262 is known and fixed, and is not subject according to a duty cycle, that is in part determined by to the line voltage or load magnitude variations. At low feedback from the power supply output 267. Pulse width powers, those less than approximately ten (10) watts, the common mode choke which is often utilized as part of the modulated switch 262 is a switch that operates according to pulse width modulated control. Feedback to the pulse width 20 EM1 filter 120 can be replaced with inductors or resistors. As can be seen when comparing the power supply of FIG. modulated switch 262 is accomplished by utilization of 1 to that of FIG. 2 the number of components utilized is feedback circuit 270, which is presently preferred to comprise a Zener diode 275 in series with a resistor 280 and reduced. This reduces the overall cost of the power supply as well as reducing its size. optocoupler 285. Optocoupler 285 provides a feedback Referring to FIG. 3, frequency variation signal 400 is current 290 to feedback terminal 295 of pulse width modu- 25 utilized by the pulse width n~odulated switch 262 to vary its lated switch 262. The feedback current is utilized to vary the switching frequency within a frequency range. The fieduty cycle of a switch coupled between the first terminal 300 9Ue"cY variation signal 400 is provided by frequency variaand second terminal 305 and thus regulate the output tion circuit 405, which preferably comprises an oscillator voltage, current or power of the power supply. 30 that operates at a lower frequency than main oscillator 465. Although, it is presently preferred that the output voltage The frequency variation signal 400, is presently preferred to is utilized for feedback, the present invention is also capable be a triangular waveform that preferrably oscillates between of utilizing either the current or power at the power supply four point five (4.5) volts and one point five (1.5) volts. output 267 without departing from the spirit and scope of the Although the presently preferred frequency variation signal present invention. 35 400 is a triangular waveform, alternate frequency variation A ~ o r t i o n the current of at the feedback signals such as ramp signals, counter output signals or other 295 is bias power for the signals that vary in magnitude during a fixed period of time pulse width modulated switch 262. The remainder of the may be utilized as the frequency variation signal, current input at the feedback terminal 295 is utilized to The frequency variation signal 400 is provided to soft the of the pulse width switch 40 start circuit 410, During operation soft start circuit 410 is 262, with the being P ~ to the ~ also provided with pulse width modulation ~ P ~ ~ frequency signal ~ feedback current. 415 and power up signal 420. Soft start enable signal 421 A bias winding 310 is utilized to bias optocoupler 285 so goes high at power up and remains high until oscillator that a feedback current can flow when light emitting diode signal 400 reaches its peak value for the first time. Soft start 315 O ~ t O c O u ~ l e 285 r The power the 45 circuit 410 will provide a signal to or-gate 425 to reset latch bias winding 310 is also used to charge pulse width modu430 thereby deactivating conduction by the switch 435, lation capacitor 330, the energy from which is utilized to which is presently preferred to be a MOSFET, soft start power the pulse width modulated switch 262. circuit 410 will instruct switch 435 to cease conduction Overvoltage protection circuit 335 is utilized to prevent when the soft start enable signal 421 is provided and the overvoltages from propagating through to the transformer 50 magnitude of the frequency variation signal 400 is less than 235. the magnitude of pulse width modulation signal 415. In Pulse width modulated switch 262 is supplied power other words, start up circuit 410 will allow the switch 435 to during start up of the power supply by current flowing into conduct as long as soft start enable signal is high and the the first terminal 300. An embodiment of one type of magnitude of the pulse width modulation signal 415 is apparatus and method for designing a configuration for 5 s below the magnitude of frequency variation signal 400 as depicted in FIG. 4. In this way, the inrush current at startup providing power to pulse width modulated switch through first terminal 300 is disclosed in commonly owned U.S. Pat. will be limited for all cycles of operation, including the first No. 5,014,178 which is incorporated herein by reference in cycle. By limiting the inrush current during all cycles of its entirety. startup operation, the maximum current through each of the The drain terminal 300, source terminal 305 and feedback 60 components of the power supply is reduced and the maximum current rating of each component can be decreased. terminal 295 are the electrical input andlor output points of The reduction in the ratings of the components reduces the the pulse width modulated switch 262. They need not be part of a monolithic device or integrated circuit, unless the pulse cost of the power supply. Soft start signal 440 will no longer be provided by the frequency variation circuit 405 when the width modulated switch 262 is implemented utilizing a 65 frequency variation signal 400 reaches its peak magnitude. monolithic device or integrated circuit. Operation of soft start circuit 410 will now be explained. Pulse width modulated switch 262 also may have soft start capabilities. When the device to which the power Soft start circuit 410 comprises a soft start latch 450 that at

~

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its set input receives the power up signal 420 and its reset input receives the soft start signal 440. Soft start enable signal 421 is provided to one input of soft start and-gate 455 while the other input of soft start and-gate 455 is provided with an output from soft start comparator 460. The output of 5 soft start comparator 460 will be high when the magnitude of frequency variation signal 400 is less than the magnitude of pulse width modulation oscillation signal 415. me pulse width modulated switch 262 depicted in FIG, 3 also has frequency jitter functionality to help reduce the EM1 10 generated by the power supply and pulse width modulated switch 262. Operation of the frequency jitter functionality will now be explained, ~~i~ oscillator 465 has a current source 470 that is mirrored by mirror current source 475, ~~i~ oscillator drive current 615 is provided to the current ls source input 485 of PWM oscillator 480, ~h~ magnitude of the current input into current source input 485 of PWM oscillator 480 determines the frequency of the pulse width modulation oscillation signal 415 which is provided by PWM oscillator 480. In order to vary the frequency of pulse 20 width modulation oscillation signal 415, an additional current source 495 is provided within main oscillator 465. The additional current source 495 is mirrored by additional current source mirror 500, ~h~ current provided by additional current source 495 is varied as follows, F~~~~~~~~25 variation signal 400 is provided to the gate of main oscillator transistor 505. As the magnitude of frequency variation signal 400 increases so does the voltage at the source of main oscillator transistor 505, due to the increasing voltage at the gate of main oscillation transistor and the relatively 30 constant voltage drop between the gate and source of the main oscillation transistor 505. As the voltage at the source of main oscillation transistor 505 increases so does the current flowing through the main oscillation resistor 510. The current flowing through main oscillation resistor 510 is 35 the same as the current flowing through additional current source 495 which is mirrored by additional current source mirror 500. Since, the presently preferred frequency variation signal 400 is a triangular waveform having a fixed period, the magnitude of the current input by additional 40 current source mirror 500 will vary linearly with the magnitude of the rising and falling edges of the frequency variation signal 400. If the frequency variation signal 400 is a ramp signal, the frequency would linearly rise to a peak and then immediately fall to is lowest value. In this way, the 45 current provided to current source input 485 of PWM oscillator 480 is varied in a known fixed range that allows for easy and accurate frequency spread of the high frequency current generated by the pulse width modulated switch. Further, the variance of the frequency is determined by the so magnitude of the current provided by additional current source mirror 500, which is in turn a function of the resistance of main oscillation resistor 510. Frequency variation circuit 405 includes a current source 525 that produces a fixed magnitude current 530 that deter- ss mines the magnitude of the frequency of the frequency variation signal 400. Although, the presently preferred current 530 has a fixed magnitude, the frequency variation signal can be generated utilizing a variable magnitude current, if a variable current is generated the frequency 60 spread would not be fixed in time but would vary with the magnitude of current 530. The fixed magnitude current 530 is fed into first transistor 535, mirrored by second transistor 540 and fed into third transistor 545. The frequency variation signal 400 is generated by the charging and discharging 65 of frequency variation circuit capacitor 550. Frequency variation circuit capacitor 550 is presently preferred to have

8
a relatively low capacitance, which allows for integration into a monolithic chip in one embodiment of the pulse width modulated switch 262. The frequency variation signal 400 is provided to upper limit comparator 555 and lower limit comparator 560. The output of upper limit comparator 555 will be high when the magnitude of the frequency variation signal 400 exceeds the upper threshold voltage 552 which is presently preferred to be four point five (4.5) volts. The output of lower limit comparator 560 will be high when the magnitude of frequency variation signal 400 exceeds lower threshold voltage 557 which is presently preferred to be one point five volts (1.5) volts. The output of upper limit comparator 555 is provided to the frequency variation circuit inverter 565 the output of which is provided to the reset input of frequency variation circuit latch 570. The set input of frequency variation circuit latch 570 receives the output of lower limit comparator 560. In operation, the output of lower limit comparator 560 will be maintained high for the majority of each cycle of frequency variation signal 400 because the magnitude of frequency variation signal will be maintained between upper threshold 552, 4.5 volts, and the lower threshold 557, 1.5 volts. The output of upper limit comparator 555 will be low until the magnitude of frequency variation signal 400 exceeds upper level threshold 552. This means that the reset input will receive a high signal until the magnitude of the frequency variation signal 400 rises above the upper threshold signal 552. The charge signal 575 output by frequency variation circuit latch 570 will be high until the frequency variation signal 400 exceeds the upper threshold limit signal 552. When the charge signal 575 is high, transistors 585 and 595 are turned off. By turning off transistors 585 and 595 current can flow into frequency variation circuit capacitor 550, which steadily charges frequency variation circuit capacitor 550 and increases the magnitude of frequency variation signal 400. The current that flows into frequency variation circuit capacitor 550 is derived from current source 525 because the current through transistor 590 is mirrored from transistor 580, which is mirrored from transistor 535. During power up, when power-up signal 420 is low, the output of inverter 605 is high which turns on transistor 600 causing frequency variation signal 400 to go low. The frequency variation signal 400 is presently preferred to start from its lowest level to perform the soft start function during its first cycle of operation. Steady-state operation of the pulse width modulated switch 262, i.e. Don start up operation, will now be described. PWM oscillator 480 provides pulse width modulation oscillation signal 415 to pulse width modulation comparator 609, the output of which will be high when the magnitude of pulse width modulation signal 415 is greater than the magnitude of a feedback signal 296 which is a function of the input provided at feedback terminal 295. When the output of pulse width modulation comparator 609 is high or-gate 425 is triggered to go high, which in turn resets pulse width modulation latch 430, removing the on signal from the control input of switch 435, thereby turning off switch 435. Pulse width modulation latch 430 is set by clock signal 603, which is provided at the beginning of each cycle of pulse width modulation oscillator 480. Drive circuit 615, which is presently preferred to be an and-gate, receives the output of pulse width modulation latch 430, power up signal 420, and maximum duty cycle signal 607. As long as each one of the signals is high, drive signal 610 is provided to the gate of MOSFET 435, which is coupled between first terminal 300 and second terminal 305 of the pulse width modulated switch 262. When any of the output of pulse

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width modulation latch 430, power up signal 420, or maxipreferred range for input DC voltage 725 is approximately one hundred (100) to four hundred (400) volts to allow for mum duty cycle signal 607 goes low drive signal 610 is no operation based upon worldwide AC mains voltages which longer provided and switch 435 ceases conduction. range between five (85) and two hundred five Referring to FIG, 4, frequency variation signal 400 prefThe presently preferred power erably has a period, which is greater than that of pulse width 5 (265) includes harmonic filter components 910 which in combimodulated oscillation signal 415. The presently preferred nation with capacitors 720 reduce the harmonic current period for frequency variation signal 400 is twenty (20) injected back into the power grid. Transformer 730 includes milliseconds, in order to allow for a smooth start up period a primary winding 740 magnetically coupled to secondary which is suficiently longer than the period of pulse width lo winding 750. The secondary winding 750 is coupled to a modulated signal 415 which is presently preferred to be ten diode 760 that is designed to prevent current flow in the (10) microseconds. Drive signal 610 will be provided only secondary winding 750 when the regulation circuit 850 is when the magnitude of pulse width modulated signal 415 is conducting (on-state). A capacitor 770 is coupled to the less than the magnitude of frequency variation signal 400. diode 760 in order to maintain a continuous voltage on a Further, frequency variation signal 400 will be preferably load 780 which has a feedback circuit coupled to it. A initiated starting from low voltage when power up signal presently preferred feedback circuit comprises an optocou420 is provided. pler 800 and Zener diode 820. The output of optocoupler 800 Referring to FIG. 5, frequency variation signal 400 which is coupled to the feedback terminal 825 of regulation circuit is presently preferred have a period is provided 850. The presently preferred regulation circuit 850 switches to the main oscillator 465. The magnitude of the pulse width 20 On and off at a duty cycle that is constant at a given input DC modulator current 615 will approximately be the magnitude voltage 725, A regulation circuit power supply bypass of frequency variation signal 400 divided by the resistance capacitor 860 is coupled to and supplies power to regulation of resistor 510 plus the magnitude of the ~ ~ r r eproduced by nt circuit 850 when the regulation circuit 850 is in the on-state. current source 470. In this way the pulse width modulator Operation of the power supply will now be described, An current 615 vary with the magnitude of the 25 AC mains voltage is input through EM1 filter 700 into bridge variation signal 400. The result is that the frequency of pulse rectifier 710 which provides a rectified signal to power width modulation signal is varied according to the magnisupply capacitors 720 that provide input DC voltage 725 to tude of this current. It is presently preferred that the pulse primary winding 740, Regulation circuit ss0,which preferwidth modulator current source produces a constant current ably operates at a constant frequency and about constant having a magnitude of point O n e (l2.') duty cycle at a given input DC voltage 725, allows current microamperes, and that frequency variation signal induced 30 to flow through primary winding 740 during its on of current 627 varies between zero ( and eight hundred (800) 1 ' each switching cycle and acts as open circuit in its off state, nanOamperes. the When current flows through primary winding 740 transof the pulse width modulation oscillator 480 and reducing former 730 is storing energy, when no current is flowing the average magnitude and the quasi-peak magnitude at 35 through primary winding 740 any energy stored in translevels the EM1 generated the power former 730 is delivered to secondary winding 750, SecondReferring to FIG. 6, an alternate presently preferred pulse ary winding 750 then provides the energy to capacitor 770. width modulated switch 262 includes all of the same comit^^ 770 delivers power to the load 780, ~h~ voltage ponents as described with respect to FIG. 3. In addition to across the load 780 ,ill vary depending on the amount of these components, a second frequency variation circuit 40 energy stored in the transformer 730 in each switching cycle current source 660 and transistor 655 are added to the which is in turn dependent on the length of time current is frequency variation circuit 405. Transistor 655 is activated flowing through primary winding 740 in each switching only when the output of soft start latch 450 goes low. When cycle which is presently preferred to be constant at a given transistor 655 is activated the current provided to the freinput DC voltage 725, The presently preferred regulation quency variation circuit 405 increases as does the frequency 45 circuit 850 allows the voltage delivered to the load to be of frequency variation signal 400. However, transistor 655 maintained at a constant level, will only be turned on when the output of soft start latch 450 It is presently preferred that the sum of the voltage drop goes low, i.e. when the magnitude of frequency variation across optoco,pler 800 and the reverse break down voltage signal 400 first reaches the upper threshold after Power UP. of zener diode 820 is approximately equal to the desired The period 400 then 50 threshold level. When the voltage across the load 780 increase after its first half cycle. This will decreases the reaches the threshold level, current begins to flow through period of the cycle during which the frequency is spread, the optocoupler 800 and Zener diode 820 that in turn is used decreasing the range. The benefit the to disable the regulation circuit 850. Whenever regulation decreased cycle period will further decrease the quasi-peak 850 is in the off-state the regulation circuit power levels the EM1 due Vending less time at each fie- 5s supply bypass capacitor 860 is charged to the operating quency level. supply voltage, which is presently preferred to be five point Referring to FIG. 7, operation of the frequency variation seven (5.7) volts by allowing a small current to flow from circuit 405 of FIG. 6 is depicted. Frequency variation signal bypass terminal 865 to the regulation circuit power supply 400 will preferably have a period often (10) milliseconds for bypass capacitor 860. Regulation circuit power supply its first half cycle. After that, when the transistor 655 is 60 bypass capacitor 860 is used to supply power to operate turned on the period is preferably decreased to five (5) regulation circuit 850 when it is in the on-state. milliseconds. Pulse width modulated switch 262 is presently When the regulation circuit 850 is disabled, an open preferred to be a monolithic device. circuit condition is created in primary winding 740 and transformer 730 does not store energy. The energy stored in Referring to FIG. 8, a power supply comprises a bridge rectifier 710 that rectifies an input AC mains voltage. Power 65 the transformer 730 from the last cycle of regulation circuit 850 is then delivered to secondary winding 750 which in supply capacitors 720 charge with the rectified AC mains turn supplies power to the load 780. Once the remaining voltage to maintain an input DC voltage 725. A presently

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energy in transformer 750 is delivered to the load 780 the provided and the magnitude of frequency variation signal voltage of the load 780 will decrease. When the voltage at 400 is less than the magnitude of main oscillation signal 415. the load 780 decreases below the threshold level, current The presently preferred regulation circuit 850 preferably ceases to flow through optocoupler 800 and regulation comprises a monolithic device, circuit 850 resumes operation either instantaneously or s While the embodiments, applications and advantages of nearly instantaneously. the present invention have been depicted and described, The presently preferred regulation circuit 850 has a curthere are many more embodiments, applications and advanrent limit feature. The current limit turns off the regulation tages possible without deviating from the spirit of the circuit 850, when the current flowing through the regulation inventive concepts described herein. Thus, the inventions circuit 850 rises above a current threshold level. In this way 10 are not to be restricted to the preferred embodiments, regulation circuit 850 can react quickly to changes such as specification or drawings. The protection to be afforded this AC ripple that occur in the rectified AC mains voltage, and patent should therefore only be restricted in accordance with Prevents the propagation of the voltage changes to the load. the spirit and intended scope of the following claims. The current limit increases the responsiveness of the reguWhat is claimed is: lation circuit to input voltage changes and delivers constant 1s 1, A pulse width modulated switch comprising: power output independent of the AC mains input voltage. a first terminal; Although the presently preferred power supply of FIG. 8 a second terminal; utilizes current mode regulation and a feedback circuit that a switch comprising a control input, said switch allowing includes an optocoupler and Zener diode, the present invena signal to be transmitted between said first terminal tion is not to be construed as to be limited to such a feedback 20 and said second terminal according to a drive signal method or circuit. Either current or voltage mode regulation provided at said control input; may be utilized by the present invention without departing a frequency variation circuit that provides a frequency from the spirit and scope of the present invention so long as variation signal; a signal indicative of the power supplied to the load is supplied to the feedback terminal 825 of the regulation 25 an oscillator that provides an oscillation signal having a circuit 850. Additionally, although the presently preferred frequency range, said frequency of said oscillation power supplies both utilize an optocoupler and Zener diode signal varying within said frequency range according to as part of feedback circuits other feedback circuits may be said frequency variation signal, said oscillator further utilized by the present invention without departing from the providing a maximum duty cycle signal comprising a 30 spirit and scope of the present invention. first state and a second state; and Regulation circuit 850 also may have integrated soft start a drive circuit that provides said drive signal when said capabilities. When the device to which the power supply is maximum duty cycle signal is in said first state and a coupled is switched on, a power up signal is generated magnitude of said oscillation signal is below a variable within the internal circuitry of regulation circuit 850. A 35 threshold level. power up signal is used to trigger soft start circuitry that 2, The pulse width modulated switch of claim 1 wherein reduces the duty cycle of the switch that operates within the said first terminal, said second terminal, said switch, said pulse width n~odulated switch 262 for a predetermined oscillator, said frequency variation circuit and said drive period of time, which is presently preferred to be ten (10) circuit comprise a monolithic device, milliseconds. Once soft start operation is completed, regu- 40 3, The pulse width modulated switch of claim 1 wherein lation circuit 850 operates according to its regular duty said frequency variation circuit comprises an additional cycle. oscillator that provides said frequency variation signal to Alternatively, or in addition to soft start functionality, said oscillator, said frequency of said oscillation signal regulation circuit 850 may also have frequency jitter funcvarying within said frequency range according to said fretionality. That is, the switching frequency of the regulation 45 quency variation signal. 4. The pulse width modulated switch of claim 1 further circuit 850 varies according to an internal frequency variation signal. This has an advantage over the frequency jitter comprising a soft start circuit that provides a signal instmctoperation of FIG. 1 in that the frequency range of the ing said drive circuit to discontinue said drive signal when presently regulation circuit 850 is known and fixed, and is said magnitude of said oscillation signal is greater than a not subject to the line voltage or load magnitude variations. magnitude of said frequency variation signal. 5. The pulse width modulated switch of claim 4 wherein Referring to FIG. 9, frequency variation circuit 405 and said additional oscillator provides a soft start signal, and main oscillator 465 function as described with respect to wherein said soft start circuit ceases operation when said FIG. 3. In operation it is the variance of the high and low soft start signal is removed. states of maximum duty cycle signal 607 that generates the 6. The pulse width n~odulated circuit of claim 5 wherein frequency jitter functionality of the regulation circuit 850. A 55 said additional oscillator further comprises presently preferred regulation circuit 850 and its steady-state operation is depicted and described in copending patent a comparator that provides a comparator signal when a application Ser. No. 091032,520 which is hereby incorpomagnitude of a reference signal is greater than or equal rated by reference in its entirety. to a magnitude of said frequency variation signal, and The regulation circuit of FIG. 9 can be modified to include 60 an inverter that receives said comparator signal and a second current source to further increase the period of provides said soft start signal. main oscillation signal 415 which achieves the same result 7. The pulse width modulated switch of claim 1 wherein and function as described with respect of FIGS. 6 and 7. said frequency of said oscillation signal varies within said The soft start functionality of the presently preferred frequency range with a magnitude of said frequency variaregulation circuit 850 of FIG. 9, will shorten the on-time of 65 tion signal. switch 435 to less than the time of the maximum duty cycle 8. The pulse width modulated switch of claim 1 wherein said oscillator comprises a an input that receives said signal 607 as long as the soft start enable signal 421 is

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frequency variation signal and a current source, wherein said 12. The regulation circuit of claim 11 wherein said frequency of said oscillation signal is a function of a sum of frequency variation circuit comprises an oscillator that proa magnitude of a current provided by said current source and vides said frequency variation signal. a magnitude of said frequency variation signal. 13. The regulation circuit of claim 11 further comprising 9. The pulse width n~odulatedswitch of claim 1 further s a soft start circuit that provides a signal instructing said drive comprising; circuit to discontinue said drive signal according to a maga rectifier comprising a rectifier input and a rectifier nitude of said frequency variation signal. output, said rectifier input receiving an AC mains signal 14. The regulation circuit of claim 13 further wherein said and said rectifier output providing a rectified signal; frequency variation circuit provides a soft start signal, and a power supply capacitor that receives said rectified signal wherein said soft start circuit ceases operation when said and provides a substantially DC signal; soft start signal is removed. 15. The regulation circuit of claim 14 wherein said a first winding comprising a first terminal and a second terminal, said first winding receiving said substantially frequency variation circuit further comprises DC signal, said second terminal of said first winding a comparator that provides a comparator signal when a coupled to said first terminal of said switch; and magnitude of a reference signal is greater than or equal a second winding magnetically coupled to said first windto a magnitude of said frequency variation signal, and ing. an inverter that receives said comparator signal and 10. The pulse width modulated switch of claim 1 wherein provides said soft start signal. said variable threshold level is a function of a feedback 20 16. The regulation circuit