| 摘要 |
PURPOSE:To protect a switching element without using an overcurrent detecting resistance, by delaying a switching signal, applying it to an overcurrent detecting circuit for detecting the voltage across the switching element, and cutting off the switching element by an output of this detecting circuit. CONSTITUTION:A switching signal of a switching signal generating circuit 1 is rectified and smoothed by a diode D1 and a capacitor C1 through a transformer T, is applied to a switching transistor TR1, and turns it on. A time constant of a delaying circuit consisting of a resistance R2 and a capacitor C2 is large and the transistor TR1 is turned on before a transistor TR2 is turned on, therefore, the transistor TR2 continues an off-state. When an overcurrent flows to the transistor TR1, the potential of a point P3 rises, accordingly the potential of a point P2 rises, the transistor TR2 is turned on, and a transistor TR3 is turned off. |
