# US 2014/0192561 A1 · Control circuit for switching power converters with synchronous rectifiers

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- Number: US 2014/0192561 A1
- Document ID: US20140192561A1
- Status: Published application
- Kind: A1
- Application number: 13/738,361
- Filed: 2013-01-10
- Published: 2014-07-10
- Earliest claimed: 2013-01-10
- Assignees: Alcatel-Lucent Canada Inc.
- Inventors: Martin Plesnik
- Web page: https://patentgrep.com/patent/US20140192561A1

## CPC

- H02M 3/33546: {with automatic control of the output voltage or current (H02M3/33561 takes precedence)}
- H02M 3/33592: {having a synchronous rectifier circuit or a synchronous freewheeling circuit at the secondary side of an isolation transformer}
- 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)
- Y02B: CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS

## Abstract

A control circuit for switching power converters with synchronous rectifiers is disclosed for providing start-up and shut-down protection. The control circuit for switching power converters with synchronous rectifiers includes a means for blocking the driving signals to the synchronous rectifiers, a voltage sampling circuit, a reference voltage, and a comparator. The comparator compares a sample voltage to a reference voltage to determine when to block and when to admit driving signals to the synchronous rectifiers. The control circuit for switching power converters with synchronous rectifiers is particularly useful for minimizing component damage due to start-up and shut-down transients as compared to converters known in the art.

## Claims

### Claim 1

A power converter fed by a primary voltage, said power converter having synchronous rectifying elements and producing a secondary voltage, the power converter comprising:
driving circuitry for said synchronous rectifying elements;
blocking circuitry connected between said driving circuitry and said synchronous rectifying elements;
secondary voltage sampling circuitry; and
control circuitry which activates said blocking circuitry in the event that said secondary voltage sampling circuitry indicates a secondary voltage below a preconfigured value.

### Claim 2 (depends on 1)

A power converter as claimed in claim 1, said control circuitry comprising:
a comparator;
said voltage sampling circuit connected to a first input of said comparator;
a reference voltage circuit connected to a second input of said comparator; and
the output of said comparator connected to said blocking circuitry for controlling blocking operation.

### Claim 3 (depends on 1)

A power converter as claimed in claim 1, further comprising:
a power transformer having primary, secondary and tertiary windings;
said secondary windings producing said secondary voltage; and
said tertiary windings connected to said driving circuitry.

### Claim 4 (depends on 2)

A power converter as claimed in claim 2, further comprising:
a local power supply circuit connected to said tertiary windings.

### Claim 5 (depends on 4)

A power converter as claimed in claim 4, said reference voltage circuit comprising:
a Zener diode and a resistor in series;
said resistor connected to said local power supply circuit at a proximate end;
said resistor connected at a distal end to said Zener diode;
said Zener diode connected to a local circuit ground at the end not connected to the resistor; and
the junction of said Zener diode and said resistor connected to said comparator input.

### Claim 6 (depends on 3)

A power converter as claimed in claim 3, said local power supply circuit comprising:
a rectifying diode having an anode connected to said tertiary windings;
a filter capacitor connected to said rectifying diode; and
a load resistor.

### Claim 7

A method of controlling a power converter fed by a primary voltage and producing a secondary voltage; said power converter having synchronous rectifying elements controlled by a control voltage; the method comprising the steps of:
sensing said secondary voltage, and in the event that said secondary voltage is below a predetermined value,
blocking said control volt from reaching said synchronous rectifying element.

### Claim 8 (depends on 7)

A method as claimed in claim 7, wherein said synchronous rectifying elements comprise Field Effect Transistors.

### Claim 9 (depends on 7)

A method as claimed in claim 7, wherein said sensing step is performed by a comparator comparing said secondary voltage to a reference voltage.

### Claim 10 (depends on 9)

A method as claimed in claim 9, wherein said blocking step is performed by bipolar transistors controlled by the output of said comparator.