Active clamp controller circuit
A power converter includes an input side to receive an input voltage, and an output side to provide an output voltage, a main switch, a controller, a transformer having a primary winding that couples the main switch to the input side, an active clamp switch coupled to the input side by an active clamp capacitor, and an active clamp controller circuit. The active clamp controller circuit includes a sampling circuit to generate a sampled main switch voltage, a delay circuit to generate a delayed sampled main switch voltage, a voltage comparison circuit, and an active clamp switch controller circuit configured to i) enable the active clamp switch based on a first comparison between the sampled main switch voltage and the delayed sampled main switch voltage, and ii) disable the active clamp switch based on a second comparison between the sampled main switch voltage and the delayed sampled main switch voltage.
1. A method comprising:
receiving, at a sampling circuit, a main switch voltage from a main switch of a power converter;
generating, at the sampling circuit, a sampled main switch voltage based on the main switch voltage;
receiving, at a delay circuit coupled to the sampling circuit, the sampled main switch voltage;
generating, by the delay circuit, a delayed sampled main switch voltage;
receiving, at a first voltage comparison circuit, the sampled main switch voltage and the delayed sampled main switch voltage;
enabling, by an active clamp switch controller circuit, an active clamp switch of the power converter based on a first comparison, by the first voltage comparison circuit, between the sampled main switch voltage and the delayed sampled main switch voltage; and
disabling, by the active clamp switch controller circuit, the active clamp switch of the power converter based on a second comparison, by the first voltage comparison circuit, between the sampled main switch voltage and the delayed sampled main switch voltage.
2. The method of claim 1 , further comprising:
disabling, by an active clamp enable circuit, the active clamp switch based on a third comparison, by a second voltage comparison circuit, of the sampled main switch voltage, irrespective of the first comparison and the second comparison of the sampled main switch voltage and the delayed sampled main switch voltage.
3. The method of claim 2 , wherein:
the third comparison comprises determining, by the second voltage comparison circuit, that the sampled main switch voltage is less than a threshold voltage that is within a threshold voltage range from a maximum voltage rating of the main switch.
4. The method of claim 3 , wherein:
the threshold voltage range is about 10 percent.
5. The method of claim 3 , wherein:
the threshold voltage range is about 20 percent.
6. The method of claim 3 , further comprising:
generating, by a digital-to-analog converter circuit, the threshold voltage based on a received digital signal.
7. The method of claim 2 , further comprising:
disabling, by the active clamp enable circuit, the active clamp switch based on the third comparison, by the second voltage comparison circuit, between the sampled main switch voltage and a threshold voltage.
8. The method of claim 7 , wherein:
the threshold voltage is generated in accordance with a piecewise function.
9. The method of claim 7 , further comprising:
generating, by a threshold generator circuit, the threshold voltage;
receiving, at the second voltage comparison circuit, the sampled main switch voltage and the threshold voltage; and
disabling, by the second voltage comparison circuit, the active clamp switch if the sampled main switch voltage is less than the threshold voltage.
10. The method of claim 1 , further comprising:
receiving, at a sampling switch, the main switch voltage;
passing, by the sampling switch, the main switch voltage to a voltage attenuation circuit when the sampling switch is enabled; and
generating, by the voltage attenuation circuit, the sampled main switch voltage based on the main switch voltage when the sampling switch is enabled.
11. The method of claim 10 , wherein:
the sampling switch is enabled for a sampling period, a beginning of the sampling period corresponding to the main switch being disabled, and an expiration of the sampling period corresponding to a voltage level of the sampled main switch voltage, the sampling switch being disabled at the expiration of the sampling period.
12. The method of claim 1 , wherein:
the active clamp switch is coupled in a series circuit combination with an active clamp capacitor.
13. A method comprising:
receiving, at a first voltage comparison circuit, a sampled main switch voltage and a delayed sampled main switch voltage, the sampled main switch voltage being based on a main switch voltage from a main switch of a power converter, the delayed sampled main switch voltage being based on the sampled main switch voltage;
enabling, by an active clamp switch controller circuit, an active clamp switch of the power converter based on a first comparison, by the first voltage comparison circuit, between the sampled main switch voltage and the delayed sampled main switch voltage; and
disabling, by the active clamp switch controller circuit, the active clamp switch of the power converter based on a second comparison, by the first voltage comparison circuit, between the sampled main switch voltage and the delayed sampled main switch voltage.
14. The method of claim 13 , further comprising:
disabling, by an active clamp enable circuit, the active clamp switch based on a third comparison, by a second voltage comparison circuit, of the sampled main switch voltage, irrespective of the first comparison and the second comparison of the sampled main switch voltage and the delayed sampled main switch voltage.
15. The method of claim 14 , wherein:
the third comparison comprises determining, by the second voltage comparison circuit, that the sampled main switch voltage is less than a threshold voltage that is within a threshold voltage range from a maximum voltage rating of the main switch.
16. The method of claim 15 , further comprising:
generating, by a threshold generator circuit, the threshold voltage;
receiving, at the second voltage comparison circuit, the sampled main switch voltage and the threshold voltage;
disabling, by the second voltage comparison circuit, the active clamp switch if the sampled main switch voltage is less than the threshold voltage.
17. The method of claim 16 , wherein:
the threshold voltage is generated in accordance with a piecewise function.
18. The method of claim 13 , further comprising:
receiving, at a sampling switch, the main switch voltage;
passing, by the sampling switch, the main switch voltage to a voltage attenuation circuit when the sampling switch is enabled; and
generating, by the voltage attenuation circuit, the sampled main switch voltage based on the main switch voltage when the sampling switch is enabled.
19. The method of claim 18 , wherein:
the sampling switch is enabled for a sampling period, a beginning of the sampling period corresponding to the main switch being disabled, and an expiration of the sampling period corresponding to a voltage level of the sampled main switch voltage, the sampling switch being disabled at the expiration of the sampling period.
20. The method of claim 13 , wherein:
the active clamp switch is coupled in a series circuit combination with an active clamp capacitor.