Double ended isolated D.C.--D.C. converter

• US 5,907,481 A
• Filed: 10/31/1997
• Issued: 05/25/1999
• Est. Priority Date: 10/31/1997
• Status: Expired due to Term

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Svardsjo, Claes
• Primary Examiner(s): Riley, Shawn
• Application Number:
  US08/962,266
• Time in Patent Office: 571 Days
• Field of Search: 363/24, 363/25, 363/26, 363/126, 363/127, 363/89
• US Class Current: 363/25
• CPC Class Codes: H02M 3/33592 having a synchronous rectifier circuit or a synchronous freewheeling circuit at the secondary side of an isolation transformer
• CPC Class Codes: 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

Abstract

A D.C.--D.C. down converter utilizes a controlled converter primary switching circuit and a full-wave rectified secondary circuit employing synchronous rectification. An isolation transformer having split first and second secondary windings supplies current to the full-wave secondary circuit. The gating signals for synchronous rectification are produced by a switch conduction control including a secondary switch control receiving control signals from the primary switch control through a control current isolating transformer. The secondary switch control is powered by the secondary converter circuit. Through the use of a split secondary winding of the isolation transformer and a full-wave rectifying circuit, the secondary converter circuit of the D.C.--D.C. converter may readily generate drive voltages for supply to the secondary switch control, allowing the secondary converter circuit and load to be fully isolated from the primary converter circuit and input source.

Claims

1. A D.C. to D.C. converter converting an input voltage from an input source to an output voltage for supply to a load, comprising:

an isolation transformer having a primary winding and a split first and second secondary windings;

a primary converter circuit including primary controlled power supply switches for selectively supplying the input voltage to said primary winding of said isolation transformer to produce a substantially symmetrical current in said primary winding;

a full wave secondary fully isolated from said primary circuit and including first and second rectifying switches each connected between a respective one of said first and second secondary windings and the load, said first and second rectifying switches being individually switchable; and

a switch conduction control controlling the conduction of said primary power supply switches, said switch conduction control further controlling conduction of said switchable first and second rectifying switches, said switch conduction control including,

a primary switch control controlling conduction of said primary controlled power supply switches,

a secondary switch control controlling conduction of said first and second rectifying switches, and

a secondary control current isolator isolating said secondary switch control from said primary switch control.

2. The D.C. to D.C. converter of claim 1 wherein said secondary control current isolator includes a secondary control isolation transformer providing control signals from said primary switch control to said secondary switch control.

3. The D.C. to D.C. converter of claim 2 wherein said secondary switch control is powered from said full wave secondary to maintain said full wave secondary and said secondary switch control fully isolated from said primary circuit.

4. The D.C. to D.C. converter of claim 2 wherein primary controlled power supply switches include a push and a pull power supply switch;

said primary switch control alternately controlling said push power supply switch to supply the input voltage to said primary winding with a first polarity and controlling said pull power supply switch to supply the input voltage with a second polarity opposite from the first polarity;

said switch control controlling said first rectifying switch to conduct supply current to said load when said push power supply switch is conductive and controlling said second rectifying switch to supply current to said load when said pull power supply switch is conductive;

said switch conduction control maintaining said first rectifying switch nonconductive when said pull power supply switch is conductive and maintaining said second rectifying switch nonconductive when said push power switch is nonconductive.

5. The D.C. to D.C. converter of claim 4 wherein said switch conduction control turns said first rectifying switch on a predetermined delay after said pull power switch is turned off and turns said second rectifying switch on a predetermined delay after said push power switch is turned off.

6. The D.C.--D.C. converter of claim 1 wherein at least one of the primary and secondary switch controls includes delay circuitry for delaying a leading edge of one of the gating pulses applied to the primary power supply switches and the first and second rectifying switches in order to establish desired "break before make" switching.

7. The D.C.--D.C. converter of claims 6 wherein the switch conduction control receives first and second pulse signals for driving the first and second primary power supply switches;

said primary switch control includes a leading edge delay and a drive buffer for each of the first and second primary power switches;

said signal isolation transformer supplying the first and second pulse signals to the secondary switch;

said secondary switch control including a trailing edge delay and inverted drive buffer for each of the first and second pulse signals, the trailing edge delay lengthening each of the first and second pulse signals which are then inverted by the inverted drive buffers to form gating signals for the first and second rectifying switches.