초록 ▼

A new single stage, single switch input current shaping circuit features substantially reduced turn-on switching losses of the switch in the flyback-converter. In this technique, the turn-on switching losses due to the discharge of the output capacitance of the switch are reduced by turning on the s

A new single stage, single switch input current shaping circuit features substantially reduced turn-on switching losses of the switch in the flyback-converter. In this technique, the turn-on switching losses due to the discharge of the output capacitance of the switch are reduced by turning on the switch when its voltage is minimal or close to the minimal. To achieve the turn-on loss reduction for a wide range of line and load conditions, the flyback-converter stage is continuously operated at the boundary of the CCM and DCM by employing a variable-frequency control. In this technique the boost inductor can work either in the DCM or the CCM. The wide-bandwidth, variable-frequency control is implemented by detecting the onset of the DCM/CCM boundary and, subsequently, turning the switch on at the minimum switch voltage. The switch is turned off when the increasing primary current reaches a reference level set by the output-voltage feedback control circuit.

대표청구항 ▼

[ We claim:] [1.] A single-stage single-switch flyback converter with input current shaping and output voltage regulation, comprising in combination:rectified ac voltage means;an energy-storage inductor having a first terminal and a second terminal, said first terminal connected to said rectified ac

[ We claim:] [1.] A single-stage single-switch flyback converter with input current shaping and output voltage regulation, comprising in combination:rectified ac voltage means;an energy-storage inductor having a first terminal and a second terminal, said first terminal connected to said rectified ac voltage means;an energy-storage capacitor;a switch which is periodically closed and opened;an isolation transformer having a primary winding and a secondary winding, said primary winding connected in series with said switch across said energy-storage capacitor;a first rectifier means having a first terminal and a second terminal, said first terminal connected to said second terminal of said energy-storage inductor and said second terminal connected to the primary winding of said isolation transformer;an output-filter capacitor;a load connected across the output-filter capacitor;a second rectifier means connecting said secondary winding of said isolation transformer to said output-filter capacitor;control means for periodically closing said switch to couple said primary winding to said energy storage capacitor, wherein said control means includes a first sensing means to detect the onset of the discontinuous-current mode operation of said isolation transformer and a delay means for closing said switch at a predetermined instant after said first sensing means detects the onset of the discontinuous current mode operation of said isolation transformer in order to turn-on said switch when the voltage across said switch is substantially at a minimum value;said control means for periodically opening said switch to decouple said primary winding from said energy storage capacitor including a second sensing means to sense the current across said switch to turn off said switch when the current across said switch reaches a predetermined level.