POWER TRANSISTOR DEVICE

PURPOSE:To protect a power transistor (TR) from destruction by connecting the emitter of the power TR to a drive circuit via a reactance component provided to the emitter to suppress rapid collector current increase due to overcurrent, etc. CONSTITUTION:When a positive voltage is fed to a terminal 5, a TR Q3 is turned on to flow a base current to TRs Q1, Q2 constituting the power TR 1, which is turned on. In applying conversely, negative voltage to the terminal 5, a TR Q4 is turned on to extract a base storage charge of the TR 1, which is turned off. If an overcurrent flows due to a short-circuited load while the TR 1 is turned on, a voltage drop is caused across a reactor 9 to increase the base-emitter voltage of the TR 1 thereby decreasing the base current. Thus, the increase in collector current of the TR 1 is suppressed to prevent destruction of the TR 1.