Switched Mode Power Converter and Method of Operation Thereof

• US 20080278975A1
• Filed: 03/09/2006
• Published: 11/13/2008
• Est. Priority Date: 03/11/2005
• Status: Active Grant

• Current Assignee: NXP B.V. (NXP Semiconductors NV)
• Original Assignee: NXP B.V. (NXP Semiconductors NV)
• Inventors: Dikken, Jan, De Groot, Humphrey, Degen, Peter
• Granted Patent: US 8,665,613 B2
• Time in Patent Office: Days
• US Class Current: 363/21.18
• CPC Class Codes: H02M 3/33523 with galvanic isolation between input and output of both the power stage and the feedback loop

Abstract

The invention relates to a switched mode power converter and a method of operating such a converter A switched mode power converter according to the invention includes a transformer (2) having a primary winding (2a) and at least one secondary winding (2b) and a secondary side rectifier circuit including an output filter (6, 10) coupled to the at least one secondary winding (2b), and a secondary side active switch device (S3) coupled between the at least one secondary winding and the output filter. The converter further includes primary side and secondary side control means (12, 16, 18) for regulating the switching of the primary side and secondary side switches, respectively, and configured so as to reduce the duty cycle of the primary side switch device (S1) during a lower power mode of operation of the converter, the reduction of the duty cycle of the primary side switch being determined with reference to the duty cycle of the secondary side switch (S3). This leads to a substantial increase in the efficiency of operation in the low power mode.

Claims

1. A switched mode power converter including:

a transformer having a primary winding and at least one secondary winding;

a primary side active power switch device coupled to the primary winding for selectively applying an input voltage (V_in) to the primary winding;

a secondary side rectifier circuit including an output filter coupled to the at least one secondary winding, and a secondary side active switch device coupled between the at least one secondary winding and the output filter; and

primary side and secondary side control means for regulating the switching of the primary side and secondary side switches, respectively, and configured so as to reduce the duty cycle of the primary side switch device during a lower power mode of operation of the converter, the reduction of the duty cycle of the primary side switch being determined with reference to the duty cycle of the secondary side switches.

2. A converter of claim 1 wherein the converter is operable to selectively generate a continuous output current, and a discontinuous output current, the discontinuous output current being obtained by reducing the duty cycle of the secondary side switch device.

3. A converter of claim 1 the primary side and secondary side control means are configured to reduce the operating frequency of the converter during the lower power mode relative to that during the higher power mode.

4. A converter of claim 1 wherein the secondary side control means is arranged to receive an input signal indicative of turn-on of the primary side switch, and generate an output signal dependent on said input signal and the turn-on time of the secondary side switch which is coupled to the primary side control means.

5. A converter of claim 4 wherein the secondary side control means is configured to receive a signal indicative of the voltage across the at least one secondary winding and determine the turn-on time of the primary side switch device therefrom.

6. A converter of claim 1 wherein a capacitive means is coupled between the drain of the secondary side switch device and ground.

7. A converter of claim 1 wherein the primary side control means include a valley detection circuit for monitoring the voltage across the primary side switch device, the turn-on time of the primary side switch device being dependent on the output thereof.

8. A converter of claim 1 wherein the primary side and secondary side control means are configured to adjust the duty cycle of the primary side switch device such that it is substantially equal to that of the secondary side switch device during the lower power mode.

10. A PC power supply including a power converter of claim 1.

9. A switched mode power converter including:

a transformer having a primary winding and at least one secondary winding;

a primary side active power switch device coupled to the primary winding for selectively applying an input voltage (Vin) to the primary winding;

a secondary side rectifier circuit including an output filter coupled to the at least one secondary winding, and a secondary side active switch device coupled between the at lest one secondary winding and the output filter; and

primary side and secondary side control means for regulating the switching of the primary side and secondary side switches, respectively, and configured so as to reduce the duty cycle of the primary side switch device during a lower power mode of operation of the converter, the reduction of the duty cycle of the primary side switch being determined with reference to the duty cycle of the secondary side switch;

wherein a capacitive means is coupled between the drain of the secondary side switch device and ground; and

wherein the primary side and secondary side control means operable to adjust the switching of primary side switch device that its duty cycle is shorter than that of the secondary side switch device.

11. A method of operating a switched mode power converter including:

a transformer having a primary winding and at least one secondary winding;

a primary side active power switch device coupled to the primary winding for selectively applying an input voltage to the primary winding;

a secondary side rectifier circuit including an output filter coupled to the at least one secondary winding, and a secondary side active switch device coupled between the at least one secondary winding and the output filter; and

primary side and secondary side control means for regulating the switching of the respective switch device, the method comprising the step of reducing the duty cycle of the primary side switch device during a lower power mode relative to its duty cycle during a higher power mode of operation of the converter, the reduction of the duty cycle of the primary side switch being determined with reference to the duty cycle of the secondary side switch.

12. A method of claim 11 including the step of reducing the duty cycle of the secondary side switch device during a lower power mode of operation of the converter to generate a discontinuous output current.