| 摘要 |
PURPOSE:To prevent an MOS field effect transistor (FET) from being broken down by detecting the temperature rise of the chip of the FET accurately and cutting off a current flowing to the FET right before the FET is broken down owing to permissible output over. CONSTITUTION:The voltage of a power source V1 is set lower than the voltage of a power source V2. When the power source V1 is turned on, an FET control circuit 3 supplies the 1st high-level on control signal to the gate of a transistor (TR) Q1, which is put in switching operation. A detecting circuit 4 detects the forward voltage of the TR Q1 which is biased reversely, i.e. a diode Df and outputs a detection signal when the detected voltage exceeds a set value. When this voltage Vf drops below the set value, the detecting circuit 4 supplied the detection signal to a cutoff circuit 5, which supplies an off signal to the gate of the TR Q1. Consequently, the TR Q1 is turned off forcibly and prevented from being broken down owing to output loss over. |
