| 摘要 |
PURPOSE:To reduce the number of pins in case of IC implementation by controlling the on-off operation of the output transistor (TR) of a constant voltage circuit from an input terminal for a reference voltage. CONSTITUTION:Reference voltages VRL1 and VRL2 of comparators C13 and C23 are lower than the reference voltage VR3 of an error amplifier A13. Further, VRL1>VRL2>VR3. When a control input voltage VC is lower than VRL1, a switch TC2 turns off. An open circuit is therefore formed between the collector and emitter of the output TRQ03. A switch TC1 turns on since VRL2>VC, and currents flow through resistances R13 and R23. When constant voltage circuits mentioned above are cascaded for a level meter, control input terminals are connected successively. The output TR is turned off under the control of the control input voltage, so the collector and emitter need not be led out separately. |
