| 摘要 |
PURPOSE:To prevent an overcurrent by constituting a protective circuit from a shunt regulator, a photo-coupler and a detection resistance. CONSTITUTION:In a power circuit, an input DC power source 1 is connected with the primary side of a transformer 2 via a switching element 3 and an output voltage controller 5 is connected with an auxiliary power supply 4 to control an ON-time of said element 3. Said output voltage controller 5 is com posed of a circuit part 5-1 controlling the switching element 3 and a circuit part 5-2 detecting an output voltage and the transformer secondary side is connected with a load 14 via a rectifying and smoothing circuit 10. Further, an overcurrent protective circuit is composed of a light emitter 6-2 of photo- coupler, a light receptor 6-1, a shunt regulator 11, a current sensing resistor 12, a Zener diode 13, a diode 7, an electrolytic capacitor 8 and a current limiting resistance 9. Then, if an output current is excessive, said regulator 11 is turned ON by voltage drop in said resistor 12 and Zener voltage to shorten said ON- time of the switching element 3.
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