| 摘要 |
<p>PURPOSE:To reduce the flowing current into the tip enable signal input part by preventing the reverse current of the tip enable current by use of PNP transistor. CONSTITUTION:When the output of inverter I2 becomes ''0'' by selecting no tip, the output terminal OVT becomes high impedance. In case of this state, the current flows between base and emitter of resistor R4 and transistor Tr1 from the power supply Vcc PNP transistor Tr5 for preventing the reverse current conducts, collector of transistor Tr1 and base of transistor Tr3 becomes a low level, and the reverse current is prevented. In this case, the current flowing into the base of transistor Tr5 through the wiring ''l'' becomes a small current corresponding to the current amplification value, and the current flowing into the tip enable signal input part is reduced. Accordingly, the switching speed is elevated by making the lead wire ''l'' thin and lowering the wiring capacity, and also the transistor for preventing the reverse current is made that of a small capacity.</p> |
