Switching current synthesis circuit for power converter
View Patent ↗A control circuit of a power converter is provided. The control circuit comprises a PWM circuit, a sample circuit, and emulation circuit. The PWM circuit generates a switching signal for switching an inductor and generating a switching current of the inductor in response to a current feedback signal. The sample circuit is coupled to sample a switching current signal into a capacitor during an on time of the switching signal. The emulation circuit generates a discharge current couple to discharge the capacitor during an off time of the switching signal for generating the current feedback signal. The switching current signal is correlated to the switching current of the inductor, and the discharge current is generated in response to an input voltage of the inductor, an output voltage of the power converter, and the on time of the switching signal.
1. A control circuit of a power converter comprising:
a pulse width modulation (PWM) circuit generating a switching signal for switching an inductor and generating a switching current of the inductor in response to a current feedback signal;
a sample circuit coupled to sample a switching current signal into a capacitor during an on time of the switching signal; and
an emulation circuit generating a discharge current couple to discharge the capacitor during an off time of the switching signal for generating the current feedback signal;
wherein the switching current signal is correlated to the switching current of the inductor, and a discharge current is generated in response to an input voltage of the inductor, an output voltage of the power converter, and the on time of the switching signal.
2. The control circuit as claimed in claim 1 , wherein the emulation circuit generates a discharge time signal in accordance with the input voltage of the inductor, the output voltage of the power converter, and the on time of the switching signal, and the discharge current is coupled to discharge the capacitor in response to the discharge time signal.
3. The control circuit as claimed in claim 1 , further comprising:
a detection circuit generating a mode signal for indicating a continuous current mode (CCM) or discontinuous current mode (DCM) operation, wherein the mode signal is used for the emulation circuit to generate the discharge current.
4. The control circuit as claimed in claim 3 , wherein the detection circuit generates a control signal for modulating a slope of the discharge current.
5. The control circuit as claimed in claim 4 , wherein the detection circuit comprises:
a counter for generating the control signal.
6. The control circuit as claimed in claim 1 , wherein a slope of the discharge current is modulated in accordance with the input voltage of the inductor, the output voltage of the power converter, and the on time of the switching signal.
7. The control circuit as claimed in claim 1 , wherein a slope of the discharge current is modulated in accordance with an initial value of the switching current signal.
8. The control circuit as claimed in claim 1 , wherein the sample circuit comprises:
an amplifier receiving the switching current signal and generating a first signal in accordance with the switching current signal;
a resistor and a switch sampling the switching current signal to generate the current feedback signal; and
wherein the capacitor holding the current feedback signal after the switch is turned off.
9. A method for controlling a power converter comprising:
generating a switching signal for switching an inductor and generating a switching current of the inductor in response to a current feedback signal; and
sampling a switching current signal into a capacitor during an on time of the switching signal;
generating a discharge current to discharge the capacitor during an off time of the switching signal for generating an emulated switching current signal;
wherein the switching current signal is correlated to the switching current of the inductor, the discharge current is generated in response to an input voltage of the inductor, an output voltage of the power converter, and the on time of the switching signal, and the emulated switching current signal is coupled to generate the current feedback signal.
10. The method as claimed in claim 9 further comprising generating a discharge time signal in accordance with the input voltage of the inductor, the output voltage of the power converter and the on time of the switching signal, wherein the discharge current is coupled to discharge the capacitor in response to the discharge time signal.
11. The method as claimed in claim 9 further comprising generating a mode signal for indicating a continuous current mode (CCM) or discontinuous current mode (DCM) operation, wherein the mode signal is used to generate the discharge current.
12. The method as claimed in claim 9 , wherein a slope of the discharge current is modulated in accordance with the input voltage of the inductor, the output voltage of the power converter, and the on time of the switching signal.
13. The method as claimed in claim 9 , wherein the slope of the discharge current is modulated in accordance with an initial value of the switching current signal.
14. The method as claimed in claim 9 further comprising generating a control signal for modulating the slope of the discharge current.
15. The method as claimed in claim 14 , wherein the control signal is generated by a counter.
16. The method as claimed in claim 9 , wherein the emulated switching current signal and a ramp signal are used to generate the current feedback signal.