# US 5,703,764 A · Switched-mode power supply having standby operation

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- Number: US 5,703,764 A
- Document ID: US5703764A
- Status: Granted
- Kind: A
- Application number: 08/647,846
- Filed: 1996-05-03
- Granted: 1997-12-30
- Earliest claimed: 1995-05-23
- Assignees: Deutsche Thomson-Brandt GmbH
- Inventors: Wolfgang Hermann; Jean-Paul Louvel
- Web page: https://patentgrep.com/patent/US5703764A

## CPC

- H04N 5/63: Generation or supply of power specially adapted for television receivers
- H02M 3/33523: {with galvanic isolation between input and output of both the power stage and the feedback loop}
- H04N 3/18: Generation of supply voltages, in combination with electron beam deflecting
- 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
- H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION
- 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)
- Y02B: CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS

## Abstract

An integrated circuit achieves a burst mode standby operation for a switched-mode power supply by driving a switching transistor. One winding of a transformer is connected to inputs of two differently biased rectifier circuits and the sum of the output voltages of these circuits is applied to a control terminal of the integrated circuit.

## Claims

### Claim 1

A switched-mode power supply having standby operation with a burst mode, comprising:
a transformer including a primary winding and a secondary winding,
a switching transistor coupled in series with said primary winding,
an integrated circuit for controlling said switching transistor,
a first rectifier circuit coupled to a terminal of a third transformer winding and generating a control voltage for said integrated circuit,
a second rectifier circuit providing a voltage of opposite polarity with respect to said first rectifier circuit and having a time constant which is appreciably shorter than a time constant of the first rectifier circuit, and
the outputs of the two rectifier circuits being coupled together to produce a sum voltage, the sum voltage being coupled to a control input of the integrated circuit for inhibiting operation of the integrated circuit in case of a standby condition periodically caused by an overshooting at a time depending upon the time constant of the first rectifier circuit.

### Claim 2 (depends on 1)

The power supply according to claim 1, wherein the outputs of the two rectifier circuits are coupled to one another via a resistor, and said sum voltage is coupled via a diode to the control input of the integrated circuit.

### Claim 3 (depends on 2)

The power supply according to claim 2, wherein said sum of the two output voltages and said control voltage are coupled to the same control input of the integrated circuit.

### Claim 4 (depends on 3)

The power supply according to claim 3, wherein inputs of said first and second rectifier circuits are coupled to a same winding.

### Claim 5 (depends on 4)

The power supply according to claim 4 wherein the two time constants are approximately 1 ms and 10 ms.

### Claim 6 (depends on 1)

The power supply according to claim 1, wherein a circuit is provided which limits the maximum turn-on time of the switching transistor in the burst mode.

### Claim 7 (depends on 6)

The power supply according to claim 6, wherein the sum of the output voltages is applied to the base of a transistor, the emitter of the transistor being coupled via a first capacitor to ground and coupled via a second capacitor to a further control terminal of the integrated circuit.

### Claim 8 (depends on 7)

The power supply according to claim 7, wherein said control terminal of the integrated circuit is coupled via a resistor to an output of a mains rectifier.