| 摘要 |
PURPOSE:To prevent an oscillation transistor from damaging by canceling the magnetic flux of a choke coil of a blocking oscillator, and turning ON the transistor after the exciting energy is completely discharged. CONSTITUTION:A blocking oscillator of a witching regulator is composed of a transformer T having windings L1-L3, and a transistor (Tr) Q. In this case, a voltage drop circuit R having a series circuit of a diode D2 and a resistor R3 is connected in parallel with a series circuit of a diode D1 and a resistor R2 with the base of Tr Q to stop a current in a very low voltage range. Thus, in the blocking oscillator TR Q tends to turn ON due to the erasure of the magnetic flux of the transformer T, but a voltage is generated in the base winding L3 until the exciting energy is completely discharged from a choke coil L, it still remains in OFF state. As a result, it can prevent Tr Q from damaging due to a surge current.
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