| 摘要 |
<p>In a battery operated, remote transmitter for a consumer instrument, a microprocessor controls operation of the transmitter. The collector current path of a PNP on-off transistor is coupled between the battery and a voltage supply terminal of the microprocessor. To power up the microprocessor, a keyboard switch in the transmitter is depressed in order to ground the base of the on-off transistor and turn on the transistor. An NPN transistor forms a latch with the PNP transistor to maintain the on-off transistor conductive. After completion of the transmitter signaling, the microprocessor switches an output port to the ground state. The output port is coupled to the base of the NPN transistor and bypasses current therefrom to initiate the regenerative deactivation of the latch. With the latch deactivated, conduction of the on-off transistor is cut off. The voltage supply terminal of the microprocessor is disconnected from the battery to power down the remote transmitter. The emitter of the NPN transistor is coupled to a tap on the battery to ensure reliable self-turn-off of the microprocessor.</p> |
