Control circuit with adaptive minimum on time for power converters
View Patent ↗A control circuit includes a switch coupled to a transformer of a power converter for switching the transformer. A sampling circuit is coupled to the transformer to sample a reflected voltage of the transformer to generate a voltage signal. A switching circuit generates a switching signal to control the switch in response to the voltage signal. The minimum on time of the switching signal is changed in response to the change of an input voltage of the power converter. Because the pulse width of the reflected voltage is narrower at light load, the minimum on time of the switching signal helps the reflected voltage detection.
1. A control circuit of a power converter, comprising:
a switch coupled to a transformer for switching the transformer;
a sampling circuit coupled to the transformer for sampling a reflected voltage of the transformer to generate a voltage signal in accordance with the reflected voltage;
a switching circuit coupled to the sampling circuit for generating a switching signal to control the switch and to regulate the output of the power converter in response to the voltage signal;
a conversion circuit generating an adaptive signal correlated to an input voltage of the power converter and transmitting the adaptive signal to the switching circuit;
wherein the adaptive signal is coupled to adjust a minimum on time of the switching signal, and the minimum on time of the switching signal is inverse proportion to the input voltage of the power converter;
wherein the sampling circuit comprises:
a sample unit coupled to the transformer to generate the voltage signal by sampling the reflected voltage of the transformer; and
a sample-signal generation circuit generating at least one sample signal in response to the switching signal;
wherein the sample signal is coupled to control the sampling time of the sample unit.
2. The control circuit of the power converter as claimed in claim 1 , wherein the switching circuit comprises a blanking circuit for generating a blanking signal in response to the switching signal, in which the blanking signal determines the minimum on time of the switching signal once the switching signal is switched on.
3. The control circuit of the power converter as claimed in claim 2 , wherein the blanking circuit is further coupled to receive the adaptive signal to adjust the minimum on time of the switching signal.
4. The control circuit as claimed in claim 1 , wherein the adaptive signal includes a minimum value to determine the minimum on time of the switching signal.
5. The control circuit of the power converter as claimed in claim 1 , wherein the conversion circuit comprises:
a voltage-to-current converter generating a current signal in response to the input voltage of the power converter;
a current source generating a current; and
a mirror circuit generating the adaptive signal in response to the current signal and the current of the current source;
wherein the current of the current source determines a minimum value of the adaptive signal to determine the minimum on time of the switching signal.
6. The control circuit of the power converter as claimed in claim 1 , wherein the switching circuit is further coupled to receive a current sense signal of the power converter and generates the switching signal in response to the current sense signal.
7. The control circuit of the power converter as claimed in claim 1 , wherein the switch can be a power transistor or a power MOSFET.
8. A control circuit, comprising:
a switch coupled to a transformer for switching the transformer;
a sampling circuit coupled to the transformer to sample a reflected voltage of the transformer to generate a voltage signal;
a switching circuit coupled to the sampling circuit to generate a switching signal to control the switch in response to the voltage signal;
wherein a minimum on time of the switching signal is changed in response to the change of an input voltage of the power converter;
wherein the sampling circuit comprises:
a sample unit coupled to the transformer to generate a voltage signal by sampling the reflected voltage of the transformer; and
a sample-signal generation circuit generating at least one sample signal in response to the switching signal;
wherein the sample signal is coupled to control the sampling time of the sample unit, the voltage signal is used to generate the switching signal.
9. The control circuit as claimed in claim 8 , wherein the switching circuit comprises a blanking circuit for generating a blanking signal in response to the switching signal, in which the blanking signal determines the minimum on time of the switching signal once the switching signal is switched on.
10. The control circuit as claimed in claim 8 , further comprising a conversion circuit to generate an adaptive signal in response to the input voltage of the power converter, in which the adaptive signal is transmitted to the switching circuit to control the minimum on time of the switching signal.
11. The control circuit as claimed in claim 10 , wherein the adaptive signal includes a minimum value to determine the minimum on time of the switching signal.
12. The control circuit as claimed in claim 10 , wherein the conversion circuit comprises:
a voltage-to-current converter generating a current signal in response to the input voltage of the power converter;
a current source generating a current; and
a mirror circuit generating the adaptive signal in response to the current signal and the current of the current source;
wherein the current of the current source determines a minimum value of the adaptive signal to determine the minimum on time of the switching signal.
13. The control circuit as claimed in claim 8 , wherein the switching circuit is further coupled to receive a current sense signal of the power converter and generates the switching signal in response to the current sense signal.
14. The control circuit as claimed in claim 8 , wherein the switch can be a power transistor or a power MOSFET.
15. A control circuit, comprising:
a switch coupled to a transformer for switching the transformer;
a sampling circuit sampling a reflected voltage of the transformer;
a switching circuit generating a switching signal to control the switch in response to the sampling of the reflected voltage of the transformer;
wherein a minimum on time of the switching signal is varied in response to the change of an input voltage of the power converter;
wherein the sampling circuit comprises:
a sample unit coupled to the transformer for sampling the reflected voltage of the transformer; and
a sample-signal generation circuit generating at least one sample signal;
wherein the sample signal is coupled to control the sampling time of the sample unit.
16. The control circuit as claimed in claim 15 , wherein the switching circuit comprises a blanking circuit for generating a blanking signal in response to the switching signal and the input voltage, in which the blanking signal determines the minimum on time of the switching signal once the switching signal is switched on.
17. The control circuit as claimed in claim 15 , wherein the switch can be a power transistor or a power MOSFET.
18. The control circuit as claimed in claim 15 , further comprising a conversion circuit to generate an adaptive signal in response to the input voltage of the power converter, in which the adaptive signal is transmitted to the switching circuit to control the minimum on time of the switching signal;
wherein the conversion circuit comprises:
a voltage-to-current converter generating a current signal in response to the input voltage of the power converter;
a current source generating a current; and
a mirror circuit generating the adaptive signal in response to the current signal and the current of the current source;
wherein the current of the current source determines a minimum value of the adaptive signal to determine the minimum on time of the switching signal.