METHOD FOR CONTROLLING A DC-TO-DC CONVERTER

• US 20150326120A1
• Filed: 05/08/2014
• Published: 11/12/2015
• Est. Priority Date: 05/08/2014
• Status: Active Grant

• Current Assignee: ROHM Co., Ltd.
• Original Assignee: Powervation Limited (ROHM Co., Ltd.)
• Inventors: Kelin, Timur, Ryan, John, O'Shea, Cormac
• Granted Patent: US 9,584,018 B2
• Time in Patent Office: Days
• 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 the 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 such a transient condition;

wherein the transient detector comprises;

a signature calculator for calculating a time varying signature of the output voltage from the DC-DC converter; and

a

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

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

3. A control system according to claim 1, 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 delayed copies from the output voltage to provide a series of individual difference values and where the series of difference values defines the signature.

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

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

6. A control system according to claim 5, wherein the stored signature is updated whenever the output voltage returns to a stead state after a transient.

7. A DC-DC converter comprising:

a control system for maintaining the 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 upon detecting such a transient condition;

wherein the transient detector comprises;

a signature calculator for calculating a time varying signature of the output voltage from the DC-DC converter; and

a

a comparator to determine when the time varying signature extends a predefined margin from a previously stored signature a control system according to claim 1.

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

9. A DC-DC converter according to claim 8, 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.

10. A DC-DC converter according to claim 8, 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.

11. A DC-DC converter according to claim 8, 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.

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

13. A DC-DC converter according to claim 12, 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.

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

15. A DC-DC converter according to claim 13, wherein if the transient response circuit detects a negative transient the PWM pulse is increased in duration.

16. A DC-DC converter according to claim 13, 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.

17. A Pulse Width Modulation (PWM) combining circuit for combining a PWM control signal in a switching power supply with a transient control signal provided by a transient detection circuit for detecting changes in the output of the switching power supply, the PWM combining circuit comprising:

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

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

19. A PWM combining circuit according to claim 17, 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.

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

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

calculating a signature representing changes in output for the DC-DC converter;

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 the presence of a transient condition.

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

23. A method according to claim 21, further comprising providing a transient counter measure in response to detecting the presence of a transient condition.