# US 5,353,212 A · Zero-voltage switching power converter with ripple current cancellation

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- Number: US 5,353,212 A
- Document ID: US5353212A
- Status: Granted
- Kind: A
- Application number: 07/871,364
- Filed: 1992-04-20
- Granted: 1994-10-04
- Earliest claimed: 1992-04-20
- Assignees: AT&T Bell Laboratories
- Inventors: Thomas P. Loftus, Jr.
- Web page: https://patentgrep.com/patent/US5353212A

## CPC

- H02M 3/33592: {having a synchronous rectifier circuit or a synchronous freewheeling circuit at the secondary side of an isolation transformer}
- H02M 3/33571: {Half-bridge at primary side of an isolation transformer}
- H02M 1/0064: {Magnetic structures combining different functions, e.g. storage, filtering or transformation}
- H02M 3/01: {Resonant DC/DC converters}
- 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 half bridge power converter utilizes two oppositely phased power switches operated with unequal duty cycles. A magnetic arrangement with two inductance values having a ratio equal to the ratio of the unequal duty cycles is included in the converter to compensate for the unequal duty cycles.

## Claims

### Claim 1

A bridge type power converter in which conduction/non-conduction transitions of its power switching transistors occur at zero voltage,
comprising:
an input circuit for accepting a source of energy;
first and second power switching transistors connected in series circuit and the series circuit connected in shunt with the input circuit; a first conducting interval of the first power switching transistor being substantially less in duration than a second conducting interval of the second power switching transistor,
a power transformer having a primary winding connected to a common node joining the first and second power switching transistors, and a secondary winding;
a rectifier circuit connected to the secondary winding for rectifying the voltage output of the secondary winding;
an output circuit for coupling the rectified voltage of the rectifier circuit to a load to be energized;
WHEREIN THE IMPROVEMENT COMPRISES:
magnetic current ripple cancellation circuitry, including:
first and second inductance devices having inductance values in a ratio equal to a ratio of the first and second conducting intervals;
the first and second inductance devices being connected between the secondary winding and the rectifier circuit; and
the first and second inductance device being included in a loop of three inductance devices having a third inductance device shunting the secondary winding.

### Claim 2

In a converter circuit, including:
first and second power switches operated at unequal conduction intervals;
a power transformer having a primary winding connected to the first and second power switches and a secondary winding;
a rectifier circuit;
a ripple cancellation circuit interconnecting the secondary winding to the rectifier circuit and including;
first and second inductors having inductance values having a ratio equal to a ratio of the unequal conduction intervals, a third inductor connected to the first and second inductors in delta connection, and the third inductor shunting the secondary winding.

### Claim 3 (depends on 1)

A bridge type power converter, as claimed in claim 1; comprising:
a ferrite core having three parallel branches and the first, second and third inductance devices being wound on the three branches respectively.

### Claim 4 (depends on 2)

In a converter circuit as claimed in claim 2, further including:
the first, second and third inductors being wound on a ferrite core having three parallel branches.

### Claim 5

In a converter circuit, including:
first and second power switches operated at unequal conduction intervals;
a power transformer having a primary winding connected to the first and second power switches and a secondary winding;
a rectifier circuit;
a ripple cancellation circuit interconnecting the secondary winding to the rectifier circuit and including;
first and second inductors having inductance values having a ratio equal to a ratio of the unequal conduction intervals and a third inductor connected to the first and second inductors in a delta connection, and the third inductor shunting the secondary winding; and
the first, second and third inductors being wound on a ferrite core having three parallel branches.

### Claim 6

A bridge type power converter in which conduction/non-conduction transitions of its power switching transistors occur at zero voltage,
comprising:
an input circuit for accepting a source of energy;
first and second power switching transistors connected in series circuit and the series circuit connected in shunt with the input circuit; a first conducting interval of the first power switching transistor being substantially less in duration than a second conducting interval of the second power switching transistor,
a power transformer having a primary winding connected to a common node joining the first and second power switching transistors, and a secondary winding;
a rectifier circuit connected to the secondary winding for rectifying the voltage output of the secondary winding;
an output circuit for coupling the rectified voltage of the rectifier circuit to a load to be energized;
magnetic current ripple cancellation circuitry, including:
first, second and third inductance devices being connected in a loop of three inductance devices with the third inductance device shunting the secondary winding;
the first and second inductance devices having inductance values in a ratio equal to a ratio of the first and second conducting intervals;
the first and second inductance devices being connected between the secondary winding and the rectifier circuit; and
the first, second and third inductance devices being wound of a ferrite core having three parallel branches.