DC CONVERTERS

• US 20070242487A1
• Filed: 04/04/2007
• Published: 10/18/2007
• Est. Priority Date: 04/04/2006
• Status: Active Grant

• Current Assignee: Power Integrations Incorporated
• Original Assignee: Power Integrations Incorporated
• Inventors: Orr, Raymond
• Granted Patent: US 7,952,892 B2
• Time in Patent Office: Days
• US Class Current: 363/21.120
• CPC Class Codes: H02M 3/335 using semiconductor devices only

Abstract

A DC converter comprises a half bridge supply circuit and one or more flyback or forward converter output circuits, and optionally also an LLC converter whose control can determine a common variable switching frequency. The half bridge supply circuit produces a 50% duty output alternating between two input voltages, such as zero and a voltage Vin. In each flyback or forward converter output circuit, a switch connects a transformer primary to the half bridge supply circuit output in a PWM controlled manner to regulate a respective flyback or forward converter DC output which is produced by the converter output circuit, with a duty ratio less than 50% whereby switching losses are reduced. Soft switching is further facilitated by the half bridge supply circuit having two transistors controlled in a complementary manner.

Claims

1. A DC converter comprising:

a first switch coupled in series with a first diode between two input terminals for supply of an input voltage;

a second switch coupled in series with a second diode between the two input terminals;

a transformer having a primary winding coupled between a first junction of the first switch with the first diode and a second junction of the second switch with the second diode, the arrangement being such that the primary winding is coupled in series with the first and second switches between the two input terminals;

a flyback or forward DC converter output circuit connected to a secondary winding of the transformer for producing a DC output;

a control signal supplied to the first switch for switching the first transistor on and off with a substantially constant duty ratio in successive switching cycles; and

a control unit responsive to the DC output for controlling the second switch with a variable duty ratio to regulate the DC output, the second switch being switched off in each switching cycle while the first switch is on.

2. A DC converter as claimed in claim 1 wherein the constant duty ratio is substantially 50% and the variable duty ratio is up to 50%.

3. A DC converter as claimed in claim 2 wherein the first switch, first diode, input terminals, and control signal are provided in common for a plurality of instances of the second switch, second diode, transformer, flyback or forward DC converter output circuit, and control unit, each of said instances providing a respective independently regulated DC output.

4. A DC converter as claimed in claim 3 and including an LLC converter output circuit coupled to the first junction for providing an LLC output, and an LLC control circuit responsive to the LLC output for controlling a variable frequency oscillator for determining a switching cycle frequency of the control signal to regulate the LLC output.

5. A DC converter as claimed in claim 2 and including a third switch connected in parallel with the first diode, the third switch being controlled in a complementary manner to the first switch.

6. A DC converter as claimed in claim 5 and including an inductor and a capacitor coupled in series between the first junction and one of the input terminals.

7. A DC converter as claimed in claim 5 and including a capacitor connected in parallel with and augmenting parasitic capacitance of the second switch.

8. A DC converter comprising a half bridge supply circuit and a flyback or forward converter output circuit, wherein the half bridge supply circuit comprises:

a switch coupled between a first input terminal and an output point of the half bridge supply circuit, and another switch coupled between a second input terminal and said output point, the switches being controlled in a complementary manner with substantially 50% duty ratio to switch said output point alternately between input voltages supplied to the first and second input terminals;

and wherein the flyback or forward converter output circuit comprises;

a primary winding of a transformer coupled via a switch between the output point of the half bridge supply circuit and one of the input terminals, a secondary winding of the transformer and at least a rectifier and output capacitor providing a flyback or forward converter DC output, and a PWM control arrangement responsive to the DC output for controlling switching of the switch of the converter output circuit with a duty ratio less than 50% thereby to regulate the DC output, the PWM control arrangement being arranged to turn on the switch of the converter output circuit with turn on of one of the switches of the half bridge supply circuit for current flow through the primary winding, and to turn off the switch of the converter output circuit before turn off of said one of the switches of the half bridge supply circuit.

9. A DC converter as claimed in claim 8 and including a capacitor connected in parallel with and augmenting parasitic capacitance of the switch of the converter output circuit.

10. A DC converter as claimed in claim 8 wherein the flyback or forward converter output circuit includes a diode or a further switch coupled between a junction of the primary winding with the switch of the converter output circuit and another of the input terminals for limiting voltage stress on the switch of the converter output circuit.

11. A DC converter as claimed in claim 8 and including a plurality of said flyback or forward converter output circuits each coupled to a single half bridge supply circuit.

12. A DC converter as claimed in claim 11 and including a resonant mode converter coupled to the output point of the half bridge supply circuit for providing a resonant mode converter output, and a resonant mode converter control circuit responsive to the resonant mode converter output for controlling a switching frequency of the switches of the half bridge supply circuit to regulate the resonant mode converter output.

13. A DC converter as claimed in claim 8 and including a resonant mode converter coupled to the output point of the half bridge supply circuit for providing a resonant mode converter output, and a resonant mode converter control circuit responsive to the resonant mode converter output for controlling a switching frequency of the switches of the half bridge supply circuit to regulate the resonant mode converter output.

14. A DC converter as claimed in claim 13 wherein the resonant mode converter comprises an LLC converter.

15. A DC converter as claimed in claim 8 and including an inductor and a capacitor coupled in series between the output point of the half bridge supply circuit and one of the input terminals.