System General Corporation

Tso Min Chen

Ta-Yung Yang

Song-Yi Lin

Pei-Sheng Tsu

Ying Chieh Su

Jun-Jie Kuo

A switching control circuit having detection terminal, input terminal, ramp generator, program terminal, error amplifier, mix circuit, and delay circuit for power factor control is provided. The detection terminal generates a detection signal in response to the inductor discharge. An input terminal is connected for detecting a switching current signal. The program terminal determines the slew rate of the ramp signal and the maximum on-time of the switching signal. An error amplifier generates an error signal for regulating the output. A mix circuit generates a mixing signal proportional to ramp signal and the switching current signal. The switching signal is turned on in response to the detection signal, and is turned off based on the error signal. The slew rate of the mixing signal is increased in response to the increase of the input voltage. The on-time of the switching signal is increased inversely proportional to the input voltage.

Switching control circuit for discontinuous mode PFC converters

A synchronous rectifier PWM (SR-PWM) controller controls a MOSFET in response to the value of a secondary current and the status of a synchronous signal for both discontinuous and continuous operation mode. The secondary current is generated in a secondary circuit and is detected by two threshold-detection terminals of the SR-PWM controller. The SR-PWM controller produces the synchronous signal by detecting a switching signal of the transformer via a detection terminal of the SR-PWM controller. Furthermore, a delay-time is inserted after the MOSFET is turned off and before the next switching cycle starts to ensure a proper operation of the MOSFET. In one embodiment, an equivalent series resistance (ESR) of an output capacitor can be used as a sensor to detect the secondary current. Therefore, no additional current sensor is required.

PWM controller for synchronous rectifier of flyback power converter

A single stage PFC power converter is provided for performing a PFC function in a half-bridge flyback power converter. A high-side switch and a low-side switch periodically supply an input voltage to a primary winding of a transformer. When the high-side switch and low-side switch are switched off, the energy stored in the transformer will be transmitted to a secondary circuit and charged to a bulk capacitor. The bulk capacitor serves to recycle the energy and reduce the output ripple noise. A forward diode and a forward inductor serve to forward the energy of the bulk capacitor to the flowing path of the input voltage for performing PFC function.

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Taichung, Taiwan

Tso Min Chen