| 摘要 |
PURPOSE:To protect surely an overcurrent of a transistor (TR) by keeping short-circuit when it is detected that an output of a delay circuit exceeds a prescribed value for a prescribed number of time and interrupting continuously a base forward bias current of a main TR. CONSTITUTION:An anode of a thyristor 171 is connected to a base of a control TR 5 and the cathode is connected to a DC power supply 12 via a limit resistor 172 to suppress the anode current of the thyristor 171 to a prescribed value in addition to a protection circuit. Then the output terminal of the delay circuit composing of a resistor 10 and a capacitor 11 is connected to the gate of the thyristor 171 via a constant voltage diode 8 and a diode 173. When a VCE of the main TR 4 is larger than a prescribed value, the thyristor 171 and a control TR 5 are turned on with a prescribed time delay to the on-signal of the main TR 4 and the control TR 5 keeps turning-on the thyristor 171 even when a base signal of the main TR 4 is an off-signal. Thus, the damage to the main TR caused by a stress or temperature rise due to an overcurrent is prevented. |
