| 摘要 |
PURPOSE: To make a current capacity small and to perform miniaturization by providing a current clamping circuit composed of the serial circuit of a Zener diode and an npn transistor circuit on the input side of an output buffer transistor. CONSTITUTION: In the driving circuit provided with the current clamping circuit 21, when on/off signals 9S from a switching signal source are turned on, an npn transistor TR 2 is turned on, a pnp TR 3 is turned off and the emitter potential of the TR 2 rises towards the output voltage Vcc of a control power source 5. In this case, the conduction of a main circuit current I0 is detected, voltage decline is generated in a sense resistor 14, a base current is made to flow to the TR 22 with the voltage decline as a driving source, the current clamping circuit 21 is operated and the input voltage of a buffer TR 1 is clamped to the Zener voltage of the Zener diode 23. Thus, the clamping circuit 21 composed of the serial circuit of the diode 23 and the TR 22 is provided on the input side of the output buffer TR 1, the current capacity is made small and the driving circuit is made small. |
