| 摘要 |
PURPOSE:To prevent a load from the supply of uncontrolled voltage when a control pulse can not be supplied to a main switching element especially by circuit failure or the like by stopping the oscillation of a self-oscillating circuit just after the rise of an auxiliary power source. CONSTITUTION:When an input power source 1 is turned on and a self-oscillating circuit 9 starts to operate, the voltage of a capacitor 21 in an auxiliary power source 14 is raised through a main transformer 11. If the voltage of the capacitor 21 rises higher than the voltage of a Zener diode 51, current is supplied to a photocoupler 53. Light from a light emitting diode 53a is detected by a photodetecting phototransistor 53b and a trigger signal is inputted to a thyristor 55 through a resistor 54. The connection of the thyristor 55 drops the voltage applied to the self-oscillating circuit 9, so that oscillation is immediately stopped. When a control pulse can not be supplied to a main transistor 12 by circuit failure or the like, a load 13 is prevented from the supply of uncontrolled voltage. |
