Method for controlling a DC-to-DC converter

• US 9,584,018 B2
• Filed: 05/08/2014
• Issued: 02/28/2017
• Est. Priority Date: 05/08/2014
• Status: Active Grant

• Current Assignee: ROHM Co., Ltd.
• Original Assignee: Rohm Powervation Limited (ROHM Co., Ltd.)
• Inventors: Kelin, Timur, Ryan, John, O'Shea, Cormac
• Primary Examiner(s): Pham, Emily P
• Assistant Examiner(s): Moody, Kyle J
• Application Number:
  US14/273,457
• Publication Number:
  US 20150326120A1
• Time in Patent Office: 1,027 Days
• Field of Search: 323/280, 323/271, 323/272, 323/282, 323/284, 323/285
• US Class Current: 1/1
• CPC Class Codes: H02M 3/156 with automatic control of output voltage or current, e.g. switching regulators
• CPC Class Codes: H02M 3/1566 with means for compensating against rapid load changes, e.g. with auxiliary current source, with dual mode control or with inductance variation
• CPC Class Codes: H02M 3/158 including plural semiconductor devices as final control devices for a single load

Abstract

Methods and circuits for power supply arrangement and control are disclosed herein. More specifically the application relates to a control method and a controller for a DC-to-DC converter, such as a synchronous Buck converter, which implements a transient detection scheme together with response generation to allow the converter to recover from a positive and/or negative load current step in the robust way, with low undershoot/overshoot at the output voltage. The control method may be implemented by either an analog or a digital circuit. The controller may be integrated with existing controller schemes (such as voltage-mode controllers) to provide superior dynamic performance during large-signal transient conditions while providing stable operation during steady state conditions. The methods and circuits provided herein are applicable to Buck converters and Buck-derived converters such as forward, push-pull, half-bridge, and full-bridge converters.

Claims

1. A control system for maintaining an output voltage of a DC-DC converter constant the control system comprising:

a first controller operating to provide a control signal to the DC-DC converter to maintain the output voltage constant;

a transient controller for providing a second control signal, the transient controller comprising a transient detector for detecting a transient condition on the output voltage of the DC-DC converter and providing a transient control signal to the DC-DC converter to counter the transient upon detecting the transient condition;

wherein the transient detector comprises;

a signature calculator for calculating a time varying signature of the output voltage of the DC-DC converter, wherein the signature calculator comprises a multi-tap delay providing multiple delayed copies of the output voltage, and a plurality of subtractors for subtracting the multiple delayed copies of the output voltage from the output voltage to provide a series of individual difference values, wherein the series of individual difference values defines the time varying signature of the output voltage of the DC-DC converter; and

a comparator to determine when the time varying signature extends a predefined margin from a previously stored signature.

2. The control system according to claim 1, wherein the transient detector is synchronized to a synchronization signal so that the time varying signature is aligned with a calculated time varying signature with respect to a switching cycle of the DC-DC converter.

3. The control system according to claim 1, wherein the signature calculator comprises a high pass filter for filtering the output voltage.

4. The control system according to claim 1, wherein the stored signature is a signature obtained from the signature calculator during steady state operation.

5. The control system according to claim 4, wherein the stored signature is updated whenever the output voltage returns to a steady state after a transient.

6. A DC-DC converter comprising:

a control system for maintaining an output voltage of the DC-DC converter constant, the control system comprising;

a first controller operating to provide a control signal to the DC-DC converter to maintain the output voltage constant;

a transient controller for providing a second control signal, the transient controller comprising a transient detector for detecting a transient condition on the output voltage of the DC-DC converter and providing a transient control signal to the DC-DC converter to counter the transient condition upon detecting the transient condition;

wherein the transient detector comprises;

a signature calculator for calculating a time varying signature of the output voltage of the DC-DC converter, wherein the signature calculator comprises a multi-tap delay providing multiple delayed copies of the output voltage, and a plurality of subtractors for subtracting the multiple delayed copies of the output voltage from the output voltage to provide a series of individual difference values, wherein the series of individual difference values defines the time varying signature of the output voltage of the DC-DC converter; and

a comparator to determine when the time varying signature extends a predefined margin from a previously stored signature.

7. The DC-DC converter according to claim 6, further comprising a transient response circuit for providing a response to counter a detected transient.

8. The DC-DC converter according to claim 7, wherein the transient response circuit comprises a switchable current sink which may be switched to the output voltage of the DC-DC converter in response to a positive transient being detected.

9. The DC-DC converter according to claim 7, wherein the transient response circuit comprises a switchable current source which may be switched to the output voltage of the DC-DC converter in response to a negative transient being detected.

10. The DC-DC converter according to claim 7, wherein the transient response circuit includes a combiner for modifying the control signal from the first controller in response to the detection of a transient.

11. The DC-DC converter according to claim 10, wherein the control signal from the first controller is a PWM signal.

12. The DC-DC converter according to claim 11, wherein the transient response circuit provides a pulse as an output upon detecting a transient and wherein the combiner adjusts the width of a pulse in the PWM signal by a duration equal to the pulse from the transient response circuit.

13. The DC-DC converter according to claim 12, wherein if the transient response circuit detects a positive transient the PWM pulse is decreased in duration.

14. The DC-DC converter according to claim 12, wherein if the transient response circuit detects a negative transient the PWM pulse is increased in duration.

15. The DC-DC converter according to claim 12, wherein if the transient response circuit detects a negative transient and no PWM pulse is present, the combiner injects the pulse from the transient response circuit into the PWM signal.

16. A Pulse Width Modulation (PWM) combining circuit for combining a PWM control signal in a switching power supply with a transient control pulse provided by a transient detection circuit for detecting changes in an output of the switching power supply based upon differences between multiple delayed copies of an output of the switching power supply and the output of the switching power supply, the PWM combining circuit comprising:

a modifier for changing a duration of a PWM pulse by a duration equal to a duration of the transient control pulse.

17. The PWM combining circuit according to claim 16, wherein the combining circuit injects a pulse into the PWM control signal if no PWM pulse is present.

18. The PWM combining circuit according to claim 16, wherein the transient control pulse is responsive to two separate types of control pulses and where the PWM combining circuit increases the duration of the PWM pulse in response to a first type of control pulse and reduces the duration of the PWM pulse in response to a second type of control pulse.

19. The PWM combining circuit according to claim 18, wherein the combining circuit injects a pulse into the PWM control signal if no PWM pulse is present.

20. A method of detecting a transient condition on the output of a DC-DC converter, the method comprising:

calculating a time varying signature representing changes in an output voltage for the DC-DC converter, wherein the calculating includes subtracting multiple delayed copies of the output voltage from the output voltage to provide a series of individual difference values, and where the series of individual difference values defines the time varying signature;

comparing the calculated signature with a previously calculated signature of the output to determine whether the output is outside a pre-defined margin of the previously calculated signature; and

upon making such a determination determining a presence of a transient condition.

21. The method according to claim 20, wherein the signature represents changes in output over a switching cycle.

22. The method according to claim 20, further comprising providing a transient counter measure in response to detecting the presence of a transient condition.