Switch mode power supply
View Patent ↗A switch mode power supply according to the invention that can improve the reliability thereof includes a series circuit connected between the positive and negative electrodes of a DC power supply 3 , the series circuit including a capacitor 4 , a main switching device 1 , and a subsidiary switching device 2 ; a main control circuit 13 ; a subsidiary control circuit 10 ; control circuits 13 and 10 turning main switching device 1 and subsidiary switching device 2 alternately ON and OFF to obtain a DC output via a transformer 6 ; and subsidiary control circuit 10 preventing a voltage exceeding the gate breakdown voltage of subsidiary switching device 2 from being applied to the gate electrode of subsidiary switching device 2.
1. A switch mode power supply comprising:
a first series circuit connected between positive and negative electrodes of a DC power supply, the first series circuit including a main switching device and a subsidiary switching device connected in series with each other;
a transformer including a first winding on a primary side thereof and a second winding on a secondary side thereof, the first winding being disposed between the positive electrode of the DC power supply and a connection point of the main switching device and the subsidiary switching device;
a rectifying and smoothing circuit, the second winding being connected to a load via the rectifying and smoothing circuit;
a main control circuit to controllably turn the main switching device ON and OFF;
a subsidiary control circuit to controllably turn the subsidiary switching device ON and OFF;
the main control circuit and the subsidiary control circuit turning the main switching device and the subsidiary switching device ON and OFF alternately to convert a second winding voltage generated across the second winding to a DC electric voltage via the rectifying and smoothing circuit and to feed the DC electric voltage to the load;
the transformer further including a third winding and a fourth winding on the primary side thereof;
the main control circuit employing a third winding voltage generated across the third winding as a signal voltage to turn the main switching device ON and OFF, whereby the DC electric voltage fed to the load is set at a predetermined value; and
the subsidiary control circuit including a transistor and a voltage regulator, the subsidiary control circuit controlling the transistor to apply to a control terminal of the subsidiary switching device a lower one of a fourth winding voltage generated across the fourth winding and a regulation voltage of the voltage regulator, the lower one of the fourth winding voltage and the regulation voltage being equal to or higher than zero volts.
2. The switch mode power supply according to claim 1 , wherein the transformer is an insulated transformer.
3. The switch mode power supply according to claim 1 , further comprising a second series circuit connecting the first winding to the positive electrode, the second series circuit including a capacitor.
4. The switch mode power supply according to claim 3 , wherein the second series circuit further includes a reactor in series with the capacitor.
5. The switch mode power supply according to claim 3 , wherein the second series circuit includes a leakage reactance of the transformer in series with the capacitor.
6. The switch mode power supply according to claim 1 , wherein the main control circuit employs the DC electric voltage as a control power supply.
7. The switch mode power supply according to claim 1 , wherein the voltage regulator is a Zener diode.