Control circuit for measuring and regulating output current of CCM power converter
View Patent ↗A switching control circuit is provided for measuring and regulating an output current of a power converter. The power converter is operated under continuous current mode. A detection circuit generates a continuous-current signal and a peak-current signal by detecting a switching current of an inductive device. An integration circuit generates an average-current signal in response to the continuous-current signal, the peak-current signal and an off time of a switching signal. The switching control circuit generates the switching signal in response to the average-current signal. The switching signal is coupled to switch the inductive device and regulate the output current of the power converter. A time constant of the integration circuit is correlated to the switching period of the switching signal, therefore the average-current signal will be proportional to the output current.
1. A control circuit, for measuring and controlling an output current of a power converter, said control circuit comprising:
a detection circuit, for generating a continuous-current signal and a peak-current signal by detecting a switching-current signal of a transformer;
an integration circuit, for generating an average-current signal in response to said continuous-current signal, said peak-current signal and an off time of a switching signal, wherein integration circuit comprises:
a first V-to-I circuit, for generating a first-charge current in response to said continuous-current signal;
a second V-to-I circuit, for generating a second-charge current in response to said peak-current signal;
a charge capacitor; and
an integrated switch, coupled to charge said charge capacitor using said first-charge current signal and said second-charge current signal when said switching signal is disabled; and
a switching control circuit, for generating said switching signal in response to said average-current signal, wherein said switching signal is coupled to switch said transformer and regulate said output current of said power converter.
2. The control circuit as claimed in claim 1 , further comprising an oscillator to generate an oscillation signal for determining a switching frequency of said switching signal.
3. The control circuit as claimed in claim 1 , a time constant of said integration circuit being correlated with a switching period of said switching signal.
4. The control circuit as claimed in claim 1 , said detection circuit comprising:
a sampling circuit, for generating said continuous-current signal by measuring a continuous current of said switching-current signal; and
a peak detector, for generating said peak-current signal by measuring a peak value of said switching-current signal.
5. The control circuit as claimed in claim 1 , said integration circuit comprising:
an output capacitor, for generating said average-current signal; and
an output switch, for periodically conducting a voltage across said charge capacitor to said output capacitor.
6. The control circuit as claimed in claim 4 , said sampling circuit comprising:
a capacitor set, coupled to receive said switching-current signal of said transformer for generating a first-sampled signal at a first period when said switching signal is enabled;
a first capacitor, coupled to receive said switching-current signal of said transformer for generating a second-sampled signal at a second period when said switching signal is enabled; and
a second capacitor, coupled to said capacitor set and said first capacitor for generating said continuous-current signal in accordance with said first-sampled signal and said second-sampled signal.
7. A method for measuring and controlling an output current of a power converter, comprising the steps of:
generating a continuous-current signal and a peak-current signal by a detection of a switching current of an inductive device;
generating an average-current signal by an integration of said continuous-current signal, said peak-current signal with an off time of a switching signal;
generating a first-charge current in response to said continuous-current signal;
generating a second-charge current in response to said peak-current signal;
charging a charge capacitor using said first-charge current signal and said second-charge current signal when said switching signal is disabled; and
generating said switching signal in response to said average-current signal; wherein said switching signal is coupled to switch said inductive device of said power converter.
8. The method as claimed in claim 7 , further comprising a step of generating an oscillation signal for determining a switching frequency of said switching signal.
9. The method as claimed in claim 7 , a time constant of said integration being correlated with a switching period of said switching signal.
10. The method as claimed in claim 7 , said detection of said switching-current signal of said inductive device, comprising:
generating said continuous-current signal by sampling a continuous current of said switching-current signal; and
generating said peak-current signal by detecting a peak current of said switching-current signal.
11. The method as claimed in claim 7 , said integration comprising:
periodically conducting a voltage across said charge capacitor to an output capacitor for generating said average-current signal.
12. The method as claimed in claim 10 , said sampling of a continuous current of said switching-current signal, comprising:
conducting a first-sampled signal to a capacitor set at a first period when said switching signal is enabled;
conducting a second-sampled signal to a first capacitor at a second period when said switching signal is enabled; and
forming said continuous-current signal across a second capacitor in accordance with said first-sampled signal and said second-sampled signal.