CONTROL CIRCUIT FOR CURRENT AND VOLTAGE CONTROL IN A SWITCHING POWER SUPPLY

• US 20070115696A1
• Filed: 10/18/2006
• Published: 05/24/2007
• Est. Priority Date: 11/18/2005
• Status: Active Grant

• Current Assignee: MyPAQ Holdings Ltd. (Transpacific IP Group Limited)
• Original Assignee: Friwo Mobile Power GmbH
• Inventors: Berghegger, Ralf
• Granted Patent: US 7,545,654 B2
• Time in Patent Office: Days
• US Class Current: 363/16
• CPC Class Codes: H02M 3/33523 with galvanic isolation between input and output of both the power stage and the feedback loop

Abstract

The present invention refers to a circuit for current and voltage control in a switching power supply controlled on the primary side, comprising a transformer with a primary-sided and a secondary-sided main winding, wherein energy pulses are transmitted from the primary side to the secondary side. Furthermore, a primary-sided switch switches on an off a primary current through the primary-sided main winding. A primary current comparator determines a switch-off time of the switch depending on the primary current. In order to reduce the load dependency of the output voltage, the control variable is variably amplified by a feedback network and additionally the control variable is reduced depending on the output load through a correction network. To reduce noise generated by the energy-rich pulse transmissions at low frequencies and the waviness of the output voltage, the control variable is fed back to the primary current comparator so that the duration during which the primary current flows through the primary-sided main winding is reduced differently. To reduce the susceptance to failure when determining the switch-on time, a comparator voltage depending on the control variable is generated as reference.

Claims

1. Control circuit for controlling the output voltage and/or the output current in a switching power supply controlled by the primary side, the switching power supply comprising:

a transformer with a primary-sided (PW) and a secondary-sided (VS) main winding, wherein electrical energy pulses are transmitted from the primary-sided to the secondary-sided main winding,

a primary-sided switch (T1) for switching on and off the primary current through the primary-sided main winding in response to a control signal (G) of the control circuit,

a primary-sided auxiliary winding (HW), in which a voltage pulse is induced after switching off the primary-sided switch, wherein the level of the voltage pulse depends on a load at the secondary side,

a sample and holding device (S&

H) for sampling and storing a level of the voltage pulse for generating a control variable, wherein the control signal is generated on the basis of the control variable,

wherein the control circuit comprises a primary current comparator (102), which determines a switch-off point in time of the primary-sided switch depending on the primary current, and

the control variable is fed back to the primary current comparator such that the switch-off point in time of the primary-sided switch can be influenced additionally depending on the control variable such that the duration during which the primary current flows through the primary-sided main winding is reduced differently.

2. Control circuit as claimed in claim 1, which is designed such that it determines a switch-on point in time of the primary-sided switch depending on the control variable and thereby determines the duration during which no primary current flows through the main winding.

3. Control circuit as claimed in claim 1, wherein the control variable is fed back to the primary current comparator via a voltage divider.

4. Control circuit as claimed in claim 1, wherein an output of the sample holding device is connected to an amplifier (OP1) such that the control variable is amplified before the feedback.

5. Control circuit as claimed in claim 4, wherein the amplifier is an operation amplifier, and an output of the sample and holding device is connected to a non-inverting input of the operation amplifier, an output of the operation amplifier is connected to a terminal of the voltage divider, and an inverting input of the operation amplifier is connected to a network.

6. Control circuit as claimed in claim 4, wherein the voltage divider consists of a first and a second resistor (R3, R4), wherein a first terminal of the first resistor (R3) is connected to an output of the amplifier, and a second terminal of the first resistor (R3) is connected to an input of the primary current comparator and to a first terminal of the second resistor (R4);

and wherein a second terminal of the second resistor is connected to the primary current conducting terminal of the primary-sided switch.

7. Control circuit as claimed in claim 2, comprising an amplifier (OP1), wherein a non-inverting input of the amplifier is connected to an output of the sample and holding device (S&

H), an output of the amplifier is connected via a feedback network to an inverting input of the amplifier, wherein the feedback network comprises a first resistor (R1), a capacitor (C1), which is connected in series with the first resistor, a second resistor (R6), which is connected in parallel to the first resistor (R1) and the capacitor (C1), and a third resistor (R7), which is connected in series to the parallel connection of the first, the second resistor and the capacitor, and which is connected to ground.

8. Control circuit as claimed in claim 2, wherein a correction network is connected between the primary-sided auxiliary winding and the sample and holding device (S&

H) such that the voltage generated from the voltage pulse at the primary-sided auxiliary winding rises depending on a load applying at the secondary side.

9. Control circuit as claimed in claim 2, which is adapted such that it determines the switch-on time of the primary-sided switch (T1) by a comparison of the control variable with a comparator voltage, and is further adapted such that the comparator voltage is determined depending on the control variable.

10. Method of controlling the output voltage and/or output current in a power switching supply controlled by the primary side, the power switching supply comprising:

a transformer with a primary-sided (PW) and a secondary-sided (VS) main winding, wherein electrical energy pulses are transmitted from the primary-sided to the secondary-sided main winding,

a primary-sided switch (T1) for switching on and off the primary current through the primary-sided main winding in response to a control signal (G) of the control circuit, a primary-sided auxiliary winding (HW), in which a voltage pulse is induced after switching off the primary-sided switch, wherein the level of the voltage pulse depends on a load at the secondary side,

a sample and holding device (S&

H) for sampling and storing a level of the voltage pulse for generating a control variable, wherein the control signal is generated on the basis of the control variable,

the method comprising the following steps,

comparing the primary current with a reference to determine a switch-off point in time of the primary-sided switch depending on the primary current,

feeding back the control variable to a primary current comparator to influence the switch-off time of the primary-sided switch in the step of comparison in a manner that the duration during which the primary current flows through the primary-sided main winding is reduced differently.

11. Method as claimed in claim 10, wherein in a further step a switch-on point in time of the primary-sided switch is determined depending on the control variable and thus the time duration during which no primary current flows through the primary-sided main winding.

12. Method as claimed in claim 10, wherein in a further step the control variable is amplified before it is fed back.

13. Control circuit for controlling the output voltage and/or the output current in switching power supply controlled by the primary side, the switching power supply comprising:

a transformer with a primary-sided (PW) and a secondary-sided (VS) main winding, wherein electrical energy pulses are transmitted from the primary-sided to the secondary-sided main winding,

a primary-sided switch (T1) for switching on and off the primary current through the primary-sided main winding in response to a control signal (G) of the control circuit,

a primary-sided auxiliary winding (HW), in which a voltage pulse is induced after switching off the primary-sided switch, wherein the level of the voltage pulse depends on a load at the secondary side,

a sample and holding device (S&

H) for sampling and storing a level of the voltage pulse for generating a control variable, wherein the control signal is generated on the basis of the control variable,

wherein the control circuit comprises a primary current comparator (102), which determines a switch-off point in time of the primary-sided switch depending on the primary current,

the control circuit is designed such that it determines a switch-on point in time of the primary-sided switch depending on the control variable and thus defines the duration in which no primary current flows through the primary-sided main winding,

the control circuit comprises an amplifier (OP1), wherein a non-inverting input of the amplifier is connected to an output of the sample and holding device, and an output of the amplifier is connected via a feedback network to an inverting input of the amplifier, and

wherein the feedback network comprises a first resistor (R1), a capacitor (C1), which is connected in series with the first resistor, a second resistor (R6), which is connected in parallel to the first resistor (R1) and the capacitor(C1), and a third resistor (R7), which is connected in series to the parallel connection of the first, the second resistor and the capacitor and which is connected to ground.

14. Control circuit as claimed in claim 13, wherein the amplifier is an operation amplifier.

15. Control circuit as claimed in claim 13, wherein the control variable is fed back to the primary current comparator (102) such that the switch-off point in time of the primary-sided switch (T1) can be influenced additionally depending on the control variable in a manner that the time duration during which the primary current flows through the main winding is reduced differently.

16. Control circuit as claimed in claim 13, wherein a correction network is connected between the primary-sided auxiliary winding (HW) and the sample and holding device (S&

H) such that the voltage generated from the voltage pulse at the primary-sided auxiliary winding rises depending on a load applying at the secondary side.

17. Control circuit as claimed in claim 13, wherein the control circuit determines the switch-on point in time of the primary-sided switch (T1) by comparison of the control variable with a comparator voltage, and is further adapted such that the comparator voltage is determined depending on the control variable.

18. Control circuit for controlling the output voltage and/or the output current in a switching power supply controlled by the primary side, the switching power supply comprising:

a transformer with a primary-sided (PW) and a secondary-sided (VS) main winding, wherein electrical energy pulses are transmitted from the primary-sided to the secondary-sided main winding,

a primary-sided switch (T1) for switching on and off the primary current through the primary-sided main winding in response to a control signal (G) of the control circuit,

a primary-sided auxiliary winding (HW), in which a voltage pulse is induced after switching off the primary-sided switch, wherein the level of the voltage pulse depends on a load at the secondary side,

a sample and holding device (S&

H) for sampling and storing a level of the voltage pulse for generating a control variable, wherein the control signal is generated on the basis of the control variable,

wherein the control circuit comprises a primary current comparator (102) which determines a switch-off point in time of the primary-sided switch depending on the primary current, and

the control circuit is adapted such that it determines a switch-on point in time of the primary-sided switch depending on the control variable and thereby defines the duration in which no primary current flows through the primary-sided main winding,

and wherein a correction network is connected between the primary-sided auxiliary winding and the sample and holding device such that the voltage generated from the voltage pulse at the primary-sided winding rises depending on a load applying at the secondary side.

19. Control circuit as claimed in claim 18, in which the correction network at least comprises a capacitor (C2) and a resistor (R8), wherein the voltage at the capacitor depends on a load applying at the secondary side and this capacitor voltage reduces via the resistor the voltage applying at a primary-sided measuring input.

20. Control circuit as claimed in claim 18, wherein the correction network comprises at least a first, a second and a third resistor, a diode and a capacity, wherein a first terminal of the first resistor (R8) is connected to the control circuit and a second terminal of the first resistor is connected to the auxiliary winding;

wherein a first terminal of the second resistor (R9) is connected to a first terminal of the first resistor (R8) and a second terminal of the second resistor (R9) is connected to a first terminal of the capacitor (C2); and

wherein a first terminal of the third resistor (R10) is connected to a first terminal of the capacitor (C2) and a second terminal of the third resistor (R1) is connected to an anode terminal of the diode (D1), and wherein a cathode terminal of the diode (D1) is connected to the auxiliary winding, and wherein a second terminal of the capacitor (C2) is connected to ground.

21. Control circuit as claimed in claim 18, wherein the control variable is fed back to the primary current comparator (102) in a manner such that the switch-off point in time of the primary-sided switch (T1) can be influenced additionally depending on the control variable in a manner that the duration during which the primary current flows through the primary winding is reduced differently.

22. Control circuit as claimed in claim 18, comprising an amplifier (OP1), wherein a non-inverting input of the amplifier is connected to an output of the sample and holding device (S&

H), an output of the amplifier is connected to an inverting input of the amplifier via a feedback network, wherein the feedback network comprises a first resistor (R1), a capacitor (Cl), which is connected in series with the first resistor, a second resistor (R6), which is connected in parallel to the first resistor (R1) and the capacitor (C1), and a third resistor (R7), which is connected in series to the parallel connection of the first, the second resistor and the capacitor, and which is connected to ground.

23. Control circuit as claimed in claim 18, wherein the control circuit determines the switch-on point in time of the primary-sided switch (T1) by comparison of the control variable with a comparator voltage, and is further designed such that the comparator voltage is determined depending on the control variable.

24. Method for controlling the output voltage and/or the output current in a switching power supply controlled by the primary side, the switching power supply comprising:

a transformer with a primary-sided (PW) and a secondary-sided (VS) main winding, wherein electrical energy pulses are transmitted from the primary-sided to the secondary-sided main winding,

a primary-sided switch (T1) for switching on and off the primary current through the primary-sided main winding in response to a control signal (G) of the control circuit,

a primary-sided auxiliary winding (HW), in which a voltage pulse is induced after switching off the primary-sided switch, wherein the level of the voltage pulse depends on a load at the secondary side,

a sample and holding device (S&

H) for sampling and storing a level of the voltage pulse for generating a control variable, wherein the control signal is generated on the basis of the control variable,

the method comprising the following steps;

comparing the primary current with a reference to determine a switch-off time of the primary-sided switch depending on the primary current,

determining a switch-on time of the primary-sided switch depending on the control variable, whereby the duration in which no primary current flows through the primary-sided main winding is determined,

increasing the voltage generated from the voltage pulse at the secondary auxiliary winding, depending on a load applying at the secondary side.

25. Control circuit for controlling the output voltage and/or the output current in a switching power supply controlled on the primary side, the switching power supply comprising:

a transformer with a primary-sided (PW) and a secondary-sided (VS) main winding, wherein electrical energy pulses are transmitted from the primary-sided to the secondary-sided main winding,

a primary-sided switch (T1) for switching on and off the primary current through the primary-sided main winding in response to a control signal (G) of the control circuit,

a primary-sided auxiliary winding (HW), in which a voltage pulse is induced after switching off the primary-sided switch, wherein the level of the voltage pulse depends on a load at the secondary side,

wherein the control circuit comprises a sample and holding device (S&

H) for sampling and storing a level of the voltage pulse for generating a control variable, and wherein the control signal is generated on the basis of the control variable,

wherein the control circuit is designed such that it defines the switch-on point in time of the primary-sided switch depending on the control variable by comparison of the control variable with a comparator voltage and thereby defines the duration in which no primary current flows through the primary-sided main winding, and

wherein the control circuit is further designed such that the comparator voltage is determined depending on the control variable.

26. Control circuit as claimed in claim 25, wherein the control circuit additionally comprises a primary current comparator (102), which determines a switch-off point in time of the primary-sided switch depending on the primary current.

27. Control circuit as claimed in claim 25, wherein a capacitor (C3) is connected such that the comparator voltage is determined by charging the capacitor and the charging of the capacitor depends on the control variable.

28. Control circuit as claimed in claim 27, wherein the charging of the capacitor (C3) is controlled by a transistor (T2) depending on the control variable.

29. Control circuit as claimed in claim 26, in which a first amplifier (OP2) is formed within the control circuit in a manner that the control variable is amplified,

wherein a non-inverting input of the first amplifier is connected to a collector input of the first transistor (T2), an inverting input of the first amplifier is connected to an output of the sample and holding device and to a non-inverting input of a second amplifier (OP3), an output of the first amplifier is connected to a base input of the first transistor (T2), an emitter output of the first transistor (T2) is connected to a first terminal of the capacitor (C3),

the collector input of the first transistor (T2) is connected via a resistor to a constant voltage source,

the first terminal of the capacitor (C3) is connected to an inverting input of the second amplifier (OP3) and a collector input of a second transistor (T3),

an output of the second amplifier (OP3) influences a control signal (G),

a second terminal of the capacitor (C3) is connected to ground,

an emitter output of the second transistor (T3) is connected to ground,

and a base input of the second transistor (T3) is connected to an internal discharge signal.

30. Control circuit as claimed in claim 26, wherein the control variable is fed back to the primary current comparator (102) such that the switch-off time of the primary-sided switch (T1) can be influenced additionally depending on the control variable in a manner that the duration during which the primary current flows through the primary-sided main winding, is reduced differently.

31. Control circuit as claimed in claim 25, wherein the control circuit comprises a comparator (OP1), wherein a non-inverting input of the amplifier is connected to an output of the sample and holding device (S&

H), an output of the amplifier is connected via a feedback network with an inverting input of the amplifier, wherein the feedback network comprises a first resistor (R1), a capacitor (C1), which is connected in series with the first resistor, a second resistor (R6), which is connected in parallel to the first resistor (R1) and the capacitor (C1), and a third resistor (R7), which is connected in series to the parallel connection of the first, the second resistor and the capacitor, and which is connected to ground.

32. Control circuit as claimed in claim 25, wherein a correction network is connected between the primary-sided auxiliary winding (HW) and the sample holding device (S&

H) such that the voltage generated from the voltage pulse at the primary-sided auxiliary winding rises depending on a load applying at the secondary side.

33. Method of controlling the output voltage and/or the output current in a switching power supply controlled by the primary side, the switching power supply comprising:

a transformer with a primary-sided (PW) and a secondary-sided (VS) main winding, wherein electrical energy pulses are transmitted from the primary-sided to the secondary-sided main winding,

a primary-sided switch for switching on and off the primary current through the primary-sided main winding in response to a control signal (G) of the control circuit,

a primary-sided auxiliary winding, in which a voltage pulse is induced after switching off the primary-sided switch, wherein the level of the voltage pulse depends on a load at the secondary side,

a sample and holding device for sampling and storing a level of the voltage pulse for generating a control variable, wherein the control signal is generated on the basis of the control variable,

and wherein the method comprises the following steps;

comparing the control variable with a comparator voltage, wherein the comparator voltage is influenced by the control variable,

determining a switch-on point in time of the primary-sided switch depending on the result of the preceding step, whereby the duration is determined in which no primary current flows through the primary-sided main winding.