# US 5,349,515 A · Switch mode power supply with feed-forward pulse limit control

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- Number: US 5,349,515 A
- Document ID: US5349515A
- Status: Granted
- Kind: A
- Application number: 08/095,387
- Filed: 1993-07-23
- Granted: 1994-09-20
- Earliest claimed: 1992-09-17
- Assignees: RCA Thomson Licensing Corporation
- Inventors: Magdy Megeid
- Web page: https://patentgrep.com/patent/US5349515A

## CPC

- H02M 1/4258: {using a single converter stage both for correction of AC input power factor and generation of a regulated and galvanically isolated DC output voltage (H02M1/4241 takes precedence)}
- H02M 3/33507: {with automatic control of the output voltage or current, e.g. flyback converters (H02M3/33561, H02M3/33569 take precedence)}
- H02M 3/33523: {with galvanic isolation between input and output of both the power stage and the feedback loop}
- H02M 3/33569: {having several active switching elements (H02M3/3353 takes precedence)}
- H04N 5/63: Generation or supply of power specially adapted for television receivers
- H02M 1/0022: {the disturbance parameters being input voltage fluctuations}
- H02M 1/0032: {Control circuits allowing low power mode operation, e.g. in standby mode}
- Y02B 70/10: Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
- H02M: APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF (transformers H01F; dynamo-electric converters H02K47/00; controlling transformers, reactors or choke coils, control or regulation of electric motors, generators or dynamo-electric converters H02P)
- H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION
- Y02B: CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS

## Abstract

In a switch mode power supply, a full wave rectified AC mains supply voltage is produced from an AC mains supply voltage without low-pass filtering. The unfiltered rectified voltage is applied to a winding of a flyback transformer that is coupled to a switching transistor. A first plurality of current pulses are generated in the winding from the rectified voltage at a frequency that is higher than the frequency of the mains supply voltage and at peak amplitudes that vary in a manner to reduce a power factor. A second supply voltage is applied via a second switching transistor to the winding to produce in the winding a second plurality of current pulses that reduce a ripple component at an output of the power supply. The second plurality of current pulses are pulse-width modulated in a feed-forward manner during a period of the mains supply voltage in accordance with the mains supply voltage. An overload threshold point is also shifted to a higher value remotely from the peak of the mains voltage, in a feed-forward manner. This results in the power factor being less affected by load variations.

## Claims

### Claim 1

A switch mode power supply, comprising:
a source of an AC, mains supply voltage;
an inductance; a first rectifier coupled to said mains source for rectifying said mains supply voltage to apply to said inductance a rectified, first supply voltage;
switching means responsive to a switching signal for generating in said inductance pulse-width modulated current pulses from said first supply voltage at a frequency that is substantially higher than a frequency of said mains supply voltage, said current pulses being coupled from said inductance to a load circuit to energize said load circuit;
a pulse-width modulator responsive to a feedback signal for generating said switching signal in accordance with said feedback signal; and
means coupled to said pulse-width modulator and responsive to said mains supply voltage for limiting a pulse-width of said switching signal such that a limit associated with said pulse-width varies during a period of said mains supply voltage in accordance with a waveform of said mains supply voltage and such that when said pulse-width reaches said limit, a further change in said feedback signal is prevented from further changing said pulse-width in a direction that tends to exceed said limit.

### Claim 2 (depends on 1)

A power supply according to claim 1 wherein said main supply voltage is coupled to said pulse-width limiting means via a signal path that bypasses said inductance in a feed forward manner for varying said limit.

### Claim 3 (depends on 1)

A power supply according to claim 1 wherein, during said period, an increase in a magnitude of said mains supply voltage causes said limit associated with a pulse width of a given current pulse of said current pulses to decrease, and vice verse.

### Claim 4 (depends on 1)

A power supply according to claim 1 wherein said limit shifts to a higher value remotely from a peak of said main supply voltage.

### Claim 5 (depends on 1)

A power supply according to claim 1 wherein said pulse-width modulator is responsive to said main supply voltage for modulating said switching signal in accordance with said main supply voltage in a feed-forward manner when said pulse width is smaller than said limit.