| 摘要 |
PURPOSE:To simplify the structure of a constant voltage power supply device with a reduction of cost, by protecting both a control transistor and load against the overcurrent through a simple reduction control circuit consisting of a resistance and a transistor. CONSTITUTION:When the output voltage V0 of a constant voltage circuit 4 increases, the collector current IL of a control transistor TR8 reduces. Then the voltage V0 of the circuit 4 reduces to be set at a certain level at all times. On the other hand, the load resistance of a load 5 is reduced to satisfy ILXRO> VBE (RO: resistance for detection of load current; VBE: base-emitter voltage). Thus a TR15 of a reduction control circuit 10 conducts, and the potential V1 of a point 13 of connection increases. As a result, the potential of the output terminal of an operational amplifier 6 is reduced to reduce the collector current of a TR7, and accordingly the base current of the TR8 is reduced. As a result, the current IL of the TR8 is reduced. Thus the TR8 and the load 5 are protected against the overcurrent. |
