Control circuit for multi-phase, multi-channels PFC converter with variable switching frequency
View Patent ↗A switching control circuit for multi-phases PFC converters is provided. It includes a PFC-control circuit coupled to receive a first-inductor signal and a feedback signal for generating a first-switching signal. The first-switching signal is utilized to switch the first inductor for power factor correction. A phase-detection circuit detects the first-switching signal and a second-inductor signal for generating a start signal and a phase-lock signal. The start signal is developed to enable a second-switching signal. The second-switching signal is coupled to switch a second inductor. An on-time-adjust circuit is coupled to adjust the on time of the second-switching signal in accordance with the phase-lock signal. The phase-lock signal is correlated to the period between the end of the second-inductor signal and the start of the second-switching signal.
1. A switching control circuit for a power factor correction (PFC) converter, comprising:
a PFC-control circuit coupled to a first inductor and the output of the PFC converter to receive a first-inductor signal and a feedback signal for generating a first-switching signal, wherein the first-switching signal is coupled to switch the first inductor for power factor correction, wherein the first-inductor signal is correlated to the demagnetization of the first inductor;
a phase-detection circuit coupled to detect the first-switching signal and a second-inductor signal for generating a start signal and a phase-lock signal, wherein the start signal is utilized to enable a second-switching signal, and the second-switching signal is coupled to switch a second inductor, wherein the second-inductor signal is correlated to the demagnetization of the second inductor, the first inductor and the second inductor are coupled to the output of the PFC converter;
an on-time-adjust circuit coupled to adjust the on time of the second-switching signal in accordance with the phase-lock signal; and
a light-load detection circuit generating an off signal and a range signal in response to the feedback signal, wherein the phase-lock signal is correlated to the period between of the second-inductor signal and the start signal, the off signal is utilized to turn off the second-switching signal, and the range signal is coupled to program the output voltage of the PFC converter.
2. The switching control circuit as claimed in claim 1 , wherein the start signal is generated in accordance with the switching period of the first-switching signal.
3. The switching control circuit as claimed in claim 1 , wherein the on-time-adjust circuit is developed to adjust the on time of the second-switching signal for minimizing the period between the end of the second-inductor signal and the start of the start signal.
4. The switching control circuit as claimed in claim 1 , wherein the PFC-control circuit comprises:
an error amplifier generating an error signal in response to the feedback signal; and
a pulse width modulation (PWM) circuit generating the first-switching signal in response to the first-inductor signal and the error signal, wherein the first-inductor signal is coupled to enable the first-switching signal, and the error signal is utilized to determine the on time of the first-switching signal.
5. The switching control circuit as claimed in claim 4 , wherein the PWM circuit comprises:
a first ramp-signal generator generating a slope signal in response to the enabling of the first-switching signal;
an adder generating a first mixed signal in accordance with a first-current signal and the slope signal, wherein the first-current signal is correlated to a switching current of the first inductor;
a first comparator coupled to enable the first-switching signal in response to the comparison of the first-inductor signal and a threshold signal; and
a second comparator coupled to disable the first-switching signal in response to the comparison of the error signal and the first mixed signal.
6. The switching control circuit as claimed in claim 1 , wherein the phase-detection circuit comprises:
a phase-signal generator generating the start signal in accordance with the switching period of the first-switching signal, wherein the start signal is generated after a phase shift of the first-switching signal; and
a lock-signal generator generating the phase-lock signal in response to the second-inductor signal and the second-switching signal, wherein the phase-lock signal is produced in accordance with the period between the end of the second-inductor signal and the start of the second-switching signal.
7. The switching control circuit as claimed in claim 1 , wherein the on-time-adjust circuit comprises:
a flip-flop coupled to enable the second-switching signal in response to the start signal;
a second-ramp-signal generator generating a second-ramp signal in response to the second-switching signal;
an attenuator producing an attenuated signal by attenuating the error signal;
an adder generating a second mixed signal in accordance with the second-ramp signal and a second-current signal; and
a third comparator coupled to disable the second-switching signal in response to the comparison of the attenuated signal and the second mixed signal, wherein the phase-lock signal is coupled to control the attenuation of the attenuator and control the on time of the second-switching signal.
8. A control circuit for a power factor correction (PFC) converter, comprising:
a PFC-control circuit coupled to a first inductor and the output of the PFC converter to receive a first-inductor signal and a feedback signal for generating a first-switching signal; in which the first-switching signal is coupled to switch the first inductor for power factor correction, wherein the first-inductor signal is correlated to the demagnetization of the first inductor;
a phase-detection circuit coupled to detect the first-switching signal and a second-inductor signal for generating a start signal and a phase-lock signal; in which the start signal is utilized to enable a second-switching signal; the second-switching signal is coupled to switch a second inductor, wherein the second-inductor signal is correlated to the demagnetization of the second inductor; and
an on-time-adjust circuit coupled to adjust the on time of the second-switching signal in accordance with the phase-lock signal.
9. The control circuit as claimed in claim 8 , further comprising a light-load detection circuit coupled to the output the PFC converter for generating an off signal in response to the feedback signal, wherein the off signal is utilized to turn off the second-switching signal.
10. The control circuit as claimed in claim 9 , wherein the light-load detection circuit further generates a range signal coupled to program the output voltage of the PFC converter in response to the off signal.
11. The control circuit as claimed in claim 9 , wherein the light-load detection circuit is further coupled to the input of the PFC converter to detect the input voltage for generating a threshold signal, and the threshold signal is utilized to generate the off signal.
12. The control circuit as claimed in claim 8 , wherein the second-switching signal is turned off before the enabling of the start signal, which determines the maximum duty cycle of the second-switching signal.
13. The control circuit as claimed in claim 8 , wherein the start signal is generated in accordance with the switching period of the first-switching signal.
14. The control circuit as claimed in claim 8 , wherein the on-time-adjust circuit is developed to adjust the on time of the second-switching signal for minimizing the period between the disabling of the second-inductor signal and the enabling of the start signal.
15. The control circuit as claimed in claim 8 , wherein the PFC-control circuit comprises:
an error amplifier generating an error signal in response to the feedback signal; and
a pulse width modulation (PWM) circuit generating the first-switching signal in response to the first-inductor signal and the error signal, wherein the first-inductor signal is coupled to enable the first-switching signal, and the error signal is utilized to determine the on time of the first-switching signal.
16. The control circuit as claimed in claim 15 , wherein the PWM circuit comprises:
a first ramp-signal generator generating a slope signal in response to the enabling of the first-switching signal;
an adder generating a first mixed signal in accordance with a first-current signal and the slope signal, wherein the first-current signal is correlated to the switching current of the first inductor;
a first comparator coupled to enable the first-switching signal in response to the comparison of the first-inductor signal and a threshold signal; and
a second comparator coupled to disable the first-switching signal in response to the comparison of the error signal and the first mixed signal.
17. The control circuit as claimed in claim 8 , wherein the phase-detection circuit comprises:
a phase-signal generator generating the start signal in accordance with the switching period of the first-switching signal; and
a lock-signal generator generating the phase-lock signal in response to the second-inductor signal and the second-switching signal, wherein the start signal is generated after a phase shift of the first-switching signal, and the phase-lock signal is produced in accordance with the period between the disabling of the second-inductor signal and the enabling of the second-switching signal.
18. The control circuit as claimed in claim 8 , wherein the on-time-adjust circuit comprises:
a flip-flop coupled to enable the second-switching signal in response to the start signal;
a second-ramp-signal generator generating a second-ramp signal in response to the second-switching signal;
an attenuator producing an attenuated signal by attenuating the error signal;
an adder generating a second mixed signal in accordance with the second-ramp signal and a second-current signal; and
a third comparator coupled to disable the second-switching signal in response to the comparison of the attenuated signal and the second mixed signal, wherein the phase-lock signal is coupled to control the attenuation of the attenuator and control the on time of the second-switching signal.
19. A method for controlling a power factor correction (PFC) converter, comprising:
generating a first-switching signal in response to a first-inductor signal and a feedback signal, wherein the first-switching signal is coupled to switch a first inductor for power factor correction, wherein the feedback signal is correlated to the output of the PFC converter, the first-inductor signal is correlated to the demagnetization of the first inductor;
generating a second-switching signal in response to a phase-lock signal, wherein the second-switching signal is coupled to switch a second inductor; and
generating the phase-lock signal in accordance with a second-inductor signal and the second-switching signal, wherein the phase-lock signal is coupled to control the on time of the second-switching signal, wherein the second-inductor signal is correlated to the demagnetization of the second inductor, and both the first inductor and the second inductor are connected to the output of PFC converter.
20. The method for controlling a PFC converter as claimed in claim 19 , further comprising generating a start signal in accordance with the first-switching signal; the start signal is coupled to enable the second-switching signal, wherein the start signal is generated after a phase shift of the first-switching signal.
21. The method for controlling a PFC converter as claimed in claim 19 , further comprising:
generating an off signal to turn off the second-switching signal in response to the feedback signal; and
generating a range signal coupled to program the output voltage of the PFC converter in response to the feedback signal.
22. The method for controlling a PFC converter as claimed in claim 21 , wherein the off signal and the range signal are generated by comparing the feedback with a threshold signal, and the threshold signal is correlated to the input voltage.
23. The method for controlling a PFC converter as claimed in claim 19 , wherein the second-switching signal is turned off before the enabling of the start signal, which determines the maximum duty cycle of the second-switching signal.
24. The method for a controlling PFC converter as claimed in claim 19 , wherein the phase-lock signal is utilized to adjust the on time of the second-switching signal for minimizing the period between the disabling of the second-inductor signal and the enabling of the second-switching signal.