CONTROL CIRCUIT HAVING OFF-TIME MODULATION TO OPERATE POWER CONVERTER AT QUASI-RESONANCE AND IN CONTINUOUS CURRENT MODE
First Claim
1. A control circuit for a power converter, the control circuit comprising:
- a PWM circuit, generating a switching signal coupled to switch a transformer of the power converter;
a signal generation circuit, coupled to an input of the power converter to receive an input signal for generating a ramp signal and a pulse signal, the pulse signal being coupled to turn on the switching signal;
a feedback circuit, coupled to an output of the power converter for generating a feedback signal;
the feedback signal is coupled to turn off the switching signal; and
a detection circuit, coupled to the transformer for generating a valley signal in response to the waveform of the transformer, wherein the pulse signal is generated in response to the ramp signal and the valley signal, the frequency of the ramp signal is decreased in response to an increase of the input signal, and the level of the input signal is correlated to an input voltage of the power converter.
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Abstract
A control circuit is developed to adaptively operate a power converter at quasi-resonance (QR) and in a continuous current mode (CCM) to achieve high efficiency. The control circuit includes a PWM circuit generating a switching signal coupled to switch a transformer. A signal generation circuit generates a ramp signal and a pulse signal. The pulse signal is generated in response to the ramp signal for switching on the switching signal. A feedback circuit produces a feedback signal according to an output load of the power converter. The feedback signal is coupled to switch off the switching signal. A detection circuit is coupled to the transformer for generating a valley signal in response to the waveform of the transformer. The valley signal is further coupled to generate the pulse signal when the ramp signal is lower than a threshold. The level of the threshold is correlated to the feedback signal.
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Citations
14 Claims
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1. A control circuit for a power converter, the control circuit comprising:
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a PWM circuit, generating a switching signal coupled to switch a transformer of the power converter; a signal generation circuit, coupled to an input of the power converter to receive an input signal for generating a ramp signal and a pulse signal, the pulse signal being coupled to turn on the switching signal; a feedback circuit, coupled to an output of the power converter for generating a feedback signal;
the feedback signal is coupled to turn off the switching signal; anda detection circuit, coupled to the transformer for generating a valley signal in response to the waveform of the transformer, wherein the pulse signal is generated in response to the ramp signal and the valley signal, the frequency of the ramp signal is decreased in response to an increase of the input signal, and the level of the input signal is correlated to an input voltage of the power converter. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A switching control circuit for a power converter, the switching control circuit comprising:
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a PWM circuit, generating a switching signal coupled to switch a transformer of the power converter; a signal generation circuit, generating a ramp signal and a pulse signal; a feedback circuit, generating a feedback signal in accordance with an output load of the power converter; a detection circuit, coupled to the transformer for generating a valley signal in response to the waveform of the transformer, wherein the feedback signal is coupled to switch off the switching signal, the pulse signal is generated in response to the ramp signal for switching on the switching signal, the valley signal is coupled to generate the pulse signal when the ramp signal is lower than a threshold, and the level of the threshold is correlated to the feedback signal. - View Dependent Claims (10, 11, 12, 13, 14)
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Specification