Soft start circuits and techniques

Patent metadata

Field	Value
Publication number	US-9285812-B2
Application number	US-201313756922-A
Country	US
Kind code	B2
Filing date	Feb 1, 2013
Priority date	Feb 1, 2013
Publication date	Mar 15, 2016
Grant date	Mar 15, 2016

Abstract

A regulator control circuit includes a switch control signal generator to generate a switch control signal and a soft start circuit to generate a soft start signal for use by the switch control signal generator. The soft start circuit includes a soft start controller and a decreasing circuit to decrease the soft start signal in response to the soft start controller. The soft start controller may comprise a non-regulation detector to detect a non-regulation condition. Embodiments include decreasing the soft start signal in response to a non-regulation condition lasting a predetermined time, detecting the non-regulation condition in response to a maximum duty cycle of the regulator switch, generating a soft start level indicator to control decreasing the soft start signal, and maintaining the soft start signal at a predetermined relationship with respect to a feedback signal.

First claim

What is claimed is:

1. A circuit for generating a soft start signal to control conduction of a regulator switch of a regulator, comprising:
a non-regulation detection circuit configured to detect a non-regulation condition in which an output of the regulator cannot be maintained within a regulation range; and
a decreasing circuit configured to decrease the soft start signal in response to a detection by the non-regulation detection circuit of the non-regulation condition lasting for a predetermined period of time selected to ensure that the non-regulation detection was not caused by a transient event.

2. The circuit of claim 1 comprising:
a soft start capacitor,
wherein the decreasing circuit comprises
a discharge circuit for discharging the capacitor to a level having a predetermined relationship with respect to a level of a feedback signal that is proportional to the output.

3. The circuit of claim 2 wherein the non-regulation detection circuit detects the non-regulation condition in response to at least one of:
a maximum duty cycle request;
a voltage at the output of the regulator falling below a first predetermined level associated with the output of the regulator not being within the regulation range;
an input voltage to the regulator falling below a second predetermined level associated with the output of regulator not being within the regulation range; or
a voltage across terminals of the regulator switch falling below a third predetermined level associated with the output of the regulator not being within the regulation range.

4. The circuit of claim 1 wherein the non-regulation detection circuit is further configured to detect that the non-regulation condition is no longer present.

5. A regulator comprising the circuit of claim 1 wherein the regulator is a linear regulator or a switching regulator.

6. The regulator of claim 5 wherein the regulator is a switching regulator and the circuit is configured to control at least one of a duty cycle or a frequency of the regulator switch.

7. The circuit of claim 1 wherein the non-regulation condition is at least one of a dropout condition or a pre-biased startup condition.

8. A switching regulator control circuit for controlling a switching regulator comprising a switch that conducts at a duty cycle to transfer energy from an input source to an output at which a regulated output having a regulation range is provided, the switching regulator control circuit comprising:
a circuit configured to generate a control signal to control conduction of the switch at the duty cycle and having first input responsive to a soft start signal, a second input responsive to a feedback signal proportional to the regulated output, and an output at which the control signal is provided; and
a soft start circuit generating the soft start signal, the soft start circuit comprising:
a non-regulation detection circuit configured to detect a non-regulation condition in which regulated output cannot be maintained within the regulation range in response to the duty cycle being a maximum duty cycle; and
a decreasing circuit configured to decrease the soft start signal in response to the detection by the non-regulation detection circuit of the non-regulation condition.

9. The switching regulator control circuit of claim 8 wherein the decreasing circuit is configured to stop decreasing the soft start signal in response to a soft start level indicator generated by a comparator.

10. The switching regulator control circuit of claim 9 wherein the comparator is responsive to the soft start signal and to the feedback signal.

11. The switching regulator control circuit of claim 9 wherein the soft start circuit further comprises an increasing circuit configured to increase the soft start signal in response the soft start level indicator.

12. The switching regulator control circuit of claim 11 wherein the increasing circuit is configured to increase the soft start signal for a predetermined period of time.

13. The switching regulator control circuit of claim 8 wherein the decreasing circuit is configured to decrease the soft start signal in response to the detection of the non-regulation condition having lasted for a predetermined period of time selected to ensure that the non-regulation detection was not cause by a transient event.

14. The switching regulator control circuit of claim 8 wherein to control conduction of the switching regulator switch, the circuit is configured to control at least one of a duty cycle or a frequency of the switching regulator switch.

15. The switching regulator control circuit of claim 8 wherein the non-regulation condition is a dropout condition.

16. The switching regulator control circuit of claim 8 wherein the circuit is an error amplifier or a feedback comparator.

17. The switching regulator control circuit of claim 11 wherein the soft start circuit further comprises a capacitor across which the soft start signal is provided, the decreasing circuit is a discharge circuit, and the increasing circuit is a charge circuit.

18. A regulator control circuit for controlling a regulator switch that conducts to transfer energy from an input source to an output at which a regulated output is provided, the regulator control circuit comprising:
an error amplifier configured to generate an error signal to control conduction of the switch and having first input responsive to a soft start signal, a second input responsive to a feedback signal proportional to the regulated output, a first output at which the error signal is provided, and a second output at which a soft start level indicator is provided, wherein the soft start level indicator is indicative of the soft start signal having a predetermined relationship with respect to the feedback signal; and
a soft start circuit generating the soft start signal, wherein the soft start circuit comprises a decreasing circuit configured to decrease the soft start signal until the soft start level indicator transitions.

19. The regulator control circuit of claim 18 wherein the soft start circuit further comprises a capacitor across which the soft start signal is provided and a non-regulation detection circuit configured to detect a non-regulation condition in which the regulated output cannot be maintained within a regulation range, wherein the decreasing circuit is configured to discharge the capacitor beginning in response to the detection by the non-regulation detection circuit of the non-regulation condition lasting for a predetermined period of time selected ensure that the non-regulation detection was not caused by a transient event.

20. The regulator control circuit of claim 19 wherein the soft start level indicator is at a first signal level when the soft start signal is a predetermined offset amount greater than the feedback signal and at a second signal level when the soft start signal is not greater than the feedback signal by the predetermined offset amount and wherein the decreasing circuit is configured to discharge the capacitor for a period of time ending when the soft start level indicator transitions from the first signal level to the second signal level.

21. The regulator control circuit of claim 19 further comprising a charge circuit configured to charge the capacitor in response the soft start level indicator.

22. The regulator control circuit of claim 21 wherein the charge circuit is configured to charge the capacitor for a predetermined period of time.

Assignees

• Wibben Joshua
• Stoddard Robert
• Allegro Microsystems Llc

Inventors

• Wibben Joshua
• Stoddard Robert

Classifications

• H02M1/36

  Means for starting or stopping converters · CPC title

• G05F1/468 Primary

  characterised by reference voltage circuitry, e.g. soft start, remote shutdown · CPC title

• G05F1/46

  wherein the variable actually regulated by the final control device is DC (G05F1/625 takes precedence) · CPC title

• H02M3/156

  with automatic control of output voltage or current, e.g. switching regulators · CPC title