| 摘要 |
PURPOSE:To protect a switch element which supplies electric power to a load by putting the switch element in constant-current operation when an excessive current flows to the load, and turning off the switch element on detecting the terminal voltage of the switch element. CONSTITUTION:When the output of a sensor circuit 25 has a low level, a TR9 turns off and a TR8 turns on, so a TR6 turns on to supply electric power to a load 3 from a power source 2. At this time, if an excessive current due to the short circuit, etc., of the load 3 flows to the load 3, a voltage drop across a resistance 15 causes a TR9 to operate, thus putting the TR6 in constant-current operation. Then, the collector-emitter voltage of the TR6 rises and a Zener diode 12 turns on. Therefore, the TR9 turns on, so the TRs 6 and 8 turn off to cut off the power supply to the load 3. |
