Control Circuit For a Primary Controlled Switched Mode Power Supply with Improved Accuracy of the Voltage Control and Primary Controlled Switched Mode Power Supply

• US 20110025286A1
• Filed: 10/13/2008
• Published: 02/03/2011
• Est. Priority Date: 10/17/2007
• Status: Active Grant

• Current Assignee: MyPAQ Holdings Ltd. (Transpacific IP Group Limited)
• Original Assignee: Power Systems Technologies GmbH (Flex, Ltd.)
• Inventors: Malsch, Rudiger, Schroeder gennant Berghegger, Ralf
• Granted Patent: US 8,582,323 B2
• Time in Patent Office: Days
• US Class Current: 323/284
• 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 under consideration refers to a controller for a primary-side regulated control power supply unit for the regulation of the output of the primary regulated control power supply unit. The invention also concerns a method for the operation of a control power supply unit of the generic type and a pertinent control power supply unit. The controller comprises a control output (B), which can be connected with the control input of a primary-side switch (Q1) of the control power supply unit; a voltage measurement input (U), which can be connected with a primary-side auxiliary winding (L4) of a transformer (200) for the sensing of an auxiliary voltage, which is induced as a function of the secondary-side output voltage; a sample-and-hold element (SuH, SuH1) for the sensing of the auxiliary voltage; and an error amplifier (202) for a comparison of the sensed auxiliary voltage with a reference value (Vref2) and for the amplification of the deviation between the sensed auxiliary voltage and the reference value. The controller (IC2) also has a return branch for the return of the output signal of the error amplifier (202) to the voltage measurement input (U).

Claims

1. Controller for a primary-side regulated control power supply unit, comprising:

a control output (B) that can be connected to the control input of a primary-side switch (Q1) of the control power supply unit;

a voltage measurement input (U) that for sensing of an auxiliary voltage, which is induced as a function of the secondary-side output voltage, can be connected to a primary-side auxiliary winding (L4) of a transformer (200);

an error amplifier (202) for a comparison of the sensed auxiliary voltage with a reference value (Vref2) and for the amplification of the deviation between the sensed auxiliary voltage and the reference value;

wherein the controller (IC2) also has a return branch for the return of the output signal of the error amplifier (202) to the voltage measurement input (U).

2. Controller according to claim 1, also comprising a sample-and-hold element (SUH, SuH1) for sensing of the auxiliary voltage.

3. Controller according to claim 1 or 2, wherein the return branch has a return switch (M1, M2) and at least one return resistor (R12, R14) connected in series with the return switch.

4. Controller according to claim 3, wherein the return switch can be controlled in such a way that it conducts when a demagnetizing signal indicates that current does not flow in the transformer.

5. Controller according to claim 3 or 4, wherein the return switch can be controlled in such a way that it conducts when the signal at the control output (b) indicates that the primary-side switch (Q1) is switched on.

6. Controller according to at least one of the preceding claims, wherein the output signal of the error amplifier (202) also overlaps a maximum current detector comparator (204).

7. Controller according to claim 6, wherein the output of the error amplifier is connected to the input of the comparator via a voltage divider (R15, R16).

8. Controller according to at least one of the preceding claims, also comprising a voltage-time converter (TvonU) for the determination of the time point when the next switching-on of the primary-side switch will occur, as a function of the output signal of the error amplifier.

9. Primary-side regulated control power supply unit with

a transformer (200), which has a primary-side (L2) and a secondary-side (L3) main winding;

a primary-side switch (Q1) to interrupt a current that flows through the primary-side main winding;

at least one primary-side auxiliary winding (L4), in which, after the opening of the primary-side switch, an auxiliary voltage is induced to reproduce the output voltage;

and a control switch (IC2) according to at least one of the preceding claims.

10. Control power supply unit according to claim 9, wherein the voltage measurement input (U) is connected to a direct voltage potential or ground potential via a charging capacitor (C19).

11. Control power supply unit according to claim 10, wherein the primary-side auxiliary winding (L4) is connected via a series connection consisting of a first and a second resistor (R101, R103) to a first terminal of the charging capacitor (C19), and the voltage measurement input (U) is connected to a common node between the first and the second resistor.

12. Control power supply unit according to claim 9, wherein the transformer also has an additional winding (L5), which is connected to a terminal with the primary-side switch (Q1) and to another terminal with a ground potential.

13. Control power supply unit according to claim 12, wherein the additional winding (L5) has a small number of windings, preferably a single winding.

14. Control power supply unit according to claim 12 or 13, wherein between the additional winding (L5) and the primary-side switch (Q1) is a limitation resistor (R97) to limit the maximum current.

15. Control power supply unit according to one of claims 11-14, wherein a third resistor (R102) for the adaptation of the regulating behavior is located parallel to the series connection consisting of the second resistor (R103) and the charging capacitor (C19).

16. Control power supply unit according to one of claims 9-12, wherein a current measurement resistor (R93) is located between the switch (Q1) and a ground potential.

17. Method to control a primary-side switch by means of a controller (IC2) in a control power supply unit with a transformer (200), which has a primary-side (L2) and a secondary-side (L3) main winding and at least one primary-side auxiliary winding (L4), in which after opening the primary switch, an auxiliary voltage is induced to reproduce the output voltage, wherein the method comprises the following steps:

control of the primary-side switch (Q1) to interrupt a current that flows through the primary-side main winding;

sensing of the auxiliary voltage on a voltage measurement input (U) of the controller (IC2);

comparison of the sensed auxiliary voltage with a reference value (Vref2) and amplification of the deviation between the sensed auxiliary voltage and the reference value by means of an error amplifier (202);

return of the output signal of the error amplifier (202) to the voltage measurement input (U).

18. Method according to claim 17, wherein the sensing of the auxiliary voltage on a voltage measurement input (U) of the controller (IC2) is carried out by means of a sample-and-hold element (SuH, SuH1).

19. Method according to claim 17 or 18, wherein the output signal of the error amplifier (202) is returned to the voltage measurement input (U) via a return switch (M1, M2) and at least one return resistor (R12, R14), connected in series with the return switch.

20. Method according to claim 19, wherein the return switch is controlled in such a way that it conducts if a demagnetization signal indicates that current is not flowing in the transformer.

21. Method according to claim 19 or 20, wherein the return switch is controlled in such a way that it conducts if the signal on the control output (B) indicates that the primary-side switch (Q1) is switched on.

22. Method according to at least one of claims 17-21, wherein the output signal of the error amplifier (202) also overlaps a maximum current detection comparator (204).

23. Method according to claim 22, wherein the output of the error amplifier is connected to the input of the comparator (204) via a voltage divider (R15, R16).

24. Method according to one of claims 17-23, wherein the time point when the next switching-on of the primary switch will take place is determined by means of a voltage-time converter (TvonU) as a function of the output signal of the error amplifier.