| 摘要 |
PURPOSE:To protect a switching transistor for a load by blowing a fuse by increasing a load current by holding the base current of the transistor nearly constant even when an overcurrent flows through a circuit. CONSTITUTION:When load signal S is supplied as an on-signal to turn on transistor TR1, the voltage across resistance R1 is as shown by expression I where the collector-emitter voltage of TR1 is VCE1. If the current of TR2 flowing through resistance R3 is I and the base-emitter voltage is VBE2, current I flows to equalize the sum of the voltage drop across resistance R3 with current I and base-emitter voltage VBE2 OF TR2 to expression 1, and resistances R1-R4 are set to establish equation 2. If an overcurrent flows, the collector current of TR3 can be increased with the base current of TR3 held nearly constant. Consequently, fuse H is blown early to protect TR3. |
