Power supply pulse width modulation (PWM) control system

• US 6,320,768 B1
• Filed: 10/06/2000
• Issued: 11/20/2001
• Est. Priority Date: 10/06/2000
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Madigan, Michael T., Pham, Mau
• Primary Examiner(s): NGUYEN, MATTHEW VAN
• Application Number:
  US09/684,285
• Time in Patent Office: 410 Days
• Field of Search: 363/40, 363/41, 363/95, 363/97, 363/131, 323/282, 323/283
• US Class Current: 363/41
• CPC Class Codes: H02M 1/08 Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
• CPC Class Codes: H02M 3/156 with automatic control of output voltage or current, e.g. switching regulators
• CPC Class Codes: H03K 7/08 Duration or width modulation ; Duty cycle modulation

Abstract

A power supply pulse width modulation (PWM) control system uses peak current program mode (CPM) control for large duty ratios with a smooth transition to voltage mode control at small duty ratios down to zero duty ratio. The PWM control system implements the latch function in an analog, circuit in contrast with commonly employed digital solutions, further resulting in low delay times since it does not have logic and set-up delays that are associated with latches.

Claims

1. A power supply pulse width modulation (PWM) control system comprising:

a differential amplifier system having, a voltage control signal (V_C) input, a current sense (V_S) signal input and a signal output, the differential amplifier system operational to generate an output signal proportional to a difference between a current sense signal and a control voltage signal;

a capacitive PWM memory element;

a PWM memory set element operational in response to a PWM system clock signal to charge the capacitive PWM memory element;

a PWM memory discharge element operational in response to the differential amplifier system output signal to discharge the capacitive PWM memory element and to generate an analog PWM signal therefrom; and

a digital converter operational in response to the analog PWM signal to generate a digital PWM output signal therefrom.

2. The power supply PWM control system according to claim 1 wherein the capacitive PWM memory element is a capacitor.

3. The power supply PWM control system according to claim 2 wherein the PWM memory set element is a PMOS transistor.

4. The power supply PWM control system according to claim 3 wherein the PWM memory discharge element is a NMOS transistor.

5. The power supply PWM control system according to claim 4 wherein the digital converter is a non-inverting buffer.

6. The power supply PWM control system according to claim 1 further comprising a current source in cascade with the PWM memory set element, the current source operational to transfer current to the capacitive memory element in response to each PWM system clock signal.

7. The power supply PWM control system according to claim 1 wherein the differential amplifier is unbalanced.

8. The power supply PWM control system according to claim 1 wherein the differential amplifier system comprises a current source, a first PMOS transistor having a source node connected to the current source, a gate node configured as the current sense signal input, and a drain;

a second PMOS transistor having a source node connected to the current source, a gate node configured as the voltage control signal input, and a drain;

a first NMOS transistor having a gate node, a drain node connected to its gate node and further connected to the first PMOS transistor drain node, and a source node connected to a system ground; and

a second NMOS transistor having a ate node connected to the first NMOS transistor gate node, a drain node connected to the second PMOS transistor drain node, and a source node connected to the system ground.

9. The power supply PWM control system according to claim 8 wherein the second PMOS transistor is configured to have more gain than the first PMOS transistor.

10. The power supply PWM control system according to claim 1 wherein the differential amplifier system comprises a first differential stage having, the voltage control signal input and an output, a second differential stage having the current sense signal input, an input in communication with the first differential stage output, and further having the differential amplifier system output, wherein the first and second differential amplifier stages are operational to generate the output signal proportional to a difference between a current sense signal and a control voltage signal.

11. The power supply PWM control system according to claim 10 wherein the first differential stage comprises a first current source, a first PMOS transistor having a source node connected to the first current source, a gate node configured as the voltage control signal input and a drain connected to a system ground;

a second PMOS transistor having, a source node connected to the first current source, a gate node and a drain node;

an NMOS transistor having, a drain node connected to the second PMOS transistor drain node, a gate node connected to its drain node and a source node connected to the system ground; and

a first reference voltage source connected at one end to the system ground and connected at its opposite end to the second PMOS transistor gate node, wherein the first reference voltage source is operational to establish a first DC offset voltage.

12. The power supply PWM control system according to claim 11 wherein the second differential stage comprises a second current source, a third PMOS transistor having a source node connected to the second current source, a gate node configured as the current sense signal input and a drain connected to a system ground;

a fourth PMOS transistor having a source node connected to the second current source, a gate node and a drain node;

a second NMOS transistor having, a drain node connected to the fourth PMOS transistor drain node, a gate node connected to the second PMOS transistor drain node and a source node connected to the system ground; and

a second reference voltage source connected at one end to the system ground and connected at its opposite end to the fourth PMOS transistor gate node, wherein the second reference voltage source is operational to establish a second DC offset voltage and further wherein the first DC offset voltage is associated with the second NMOS transistor and is operational to establish its bias.

13. The power supply PWM control system according to claim 12 wherein the second current source is capable of providing a larger current than that provided by the first current source.

14. The power supply PWM control system according to claim 13 wherein the third and fourth PMOS transistors have a higher transconductance than that associated with the first and second PMOS transistors respectively.

15. The power supply PWM control system according to claim 14 wherein the differential amplifier system further comprises a third differential stage operational to set a transition voltage level where the current sense signal ceases to effect a duty ratio independent of other power supply PWM control system gains and bias currents.

16. The power supply PWM control system according to claim 1 wherein the differential amplifier system comprises a high speed command stage, a high speed sense stage and a differential stage having a reference capable of setting a transition voltage level where the current sense signal ceases to effect a duty ratio independent of other power supply PWM control system gains and bias currents.

17. The power supply PWM control system according to claim 16 further comprising a reference voltage source operational in association with the high speed command stage, the high speed sense stage and the differential stage to establish a voltage control signal threshold between Current Program Mode and Voltage Mode Control.

18. A power supply PWM control system comprising:

a first differential stage responsive to a voltage control signal (V_C) to generate a Voltage Mode Control signal,

a second differential stage responsive to a current sense (V_S) signal to generate a Current Program Mode Control signal;

a third differential stage in communication with the first differential stage and operational to establish a threshold for the voltage control signal associated with the first differential stage;

a capacitive PWM memory device;

a PWM memory set device operational in response to a PWM system clock signal to charge the capacitive PWM memory device;

a PWM memory discharge device operational in response to the first and second differential stage Control signals such that the capacitive PWM memory device can be discharged to generate an analog PWM signal therefrom and further such that the power supply PWM control system can transition between Current Program Mode Control and Voltage Mode Control; and

a digital converter operational in response to the analog PWM signal to generate a digital PWM output signal therefrom.

19. The power supply PWM control system according to claim 18 wherein the PWM memory device is a capacitor.

20. The power supply PWM control system according to claim 18 further comprising a first reference voltage source configured to establish a DC offset associated with the second differential stage.

21. The power supply PWN control system according to claim 20 further comprising a second reference voltage source configured to establish a DC offset associated with the PWM memory discharge device.

22. The power supply PWM control system according to claim 21 further comprising a third reference voltage source configured to establish a voltage control signal threshold between Current Program Mode Control and Voltage Mode Control.

23. A power supply pulse width modulation (PWM) control system comprising:

a differential amplifier system having a voltage control signal (V_C) input, a current sense (V_S) signal input and a signal output, the differential amplifier system operational to generate an output signal controlled by a current sense signal and a control voltage signal;

an analog latch;

a latch set element operational in response to a PWM system clock signal to set the analog latch;

a latch reset element operational in response to the differential amplifier system output signal to reset the analog latch and to generate an analog, PWM signal therefrom; and

a digital converter operational in response to the analog PWM signal to generate a digital PWM output signal therefrom.

24. The power supply PWM control system according to claim 23 wherein the analog latch comprises a capacitor.

25. The power supply PWM control system according to claim 24 wherein the latch set element comprises a MOS transistor.

26. The power supply PWM control system according to claim 25 wherein the latch reset element comprises a MOS transistor.

27. The power supply PWM control system according to claim 26 wherein the digital converter is a non-inverting buffer.

28. The power supply PWM control system according to claim 23 wherein the differential amplifier system comprises a high-speed command stage operational in response to the control voltage signal to generate a Voltage Mode Control signal.

29. The power supply PWN control system according to claim 28 wherein the differential amplifier system further comprises a high-speed sense stage operational in response to the current sense signal to generate a Current Program Mode Control signal.

30. The power supply PWM control system according to claim 29 wherein the differential amplifier system further comprises a voltage reference stage in communication with the high-speed command stage and operational to establish a control voltage signal threshold between the Voltage Mode Control signal and the Current Program Mode Control signal.

31. The power supply PWM control system according to claim 23 further comprising a first reference voltage source connected to the first differential stage such that the first reference voltage source and the first differential stage can establish an offset voltage associated with the second and third differential stages.

32. The power supply PWM control system according to claim 31 further comprising a second reference voltage source connected to the third differential stage such that the second reference voltage source and the third differential stage can establish an offset voltage associated with the latch reset element.

33. The power supply PWN control system according to claim 32 further comprising a third reference voltage source connected to the second differential stage such that the third reference voltage source and the second differential stage can establish a threshold voltage between a current sense signal and a control voltage signal.