| 摘要 |
PURPOSE:To limit a collector current of a composite transistor (TR) to a prescribed value by providing an equivalent Zener diode comprising a Zener diode and an auxiliary TR between a base and a source of a composite TR in which a bipolar TR and an FET are connected in cascode. CONSTITUTION:Since a base current IB of a main TRQ1 is decreased, the increase in a collector current IC is suppressed. Since the collector current IC having a large value is commutated to a base current supply circuit in the process that composite TRsQ1, Q2 are turned off, a collector-emitter voltage VCE3 of the auxiliary TRQ3 is increased more rapidly than the case when a Zener diode ZD2 is conducted and a Zener current IZ is added to a base current IB3 of the auxiliary TRQ3. Thus, the collector-emitter voltage is kept nearly to a constant value, most collector current IC to be commutated becomes a collector current IC3, which flows to the auxiliary TRQ3 to attain high speed turn-off. |
