| 摘要 |
PROBLEM TO BE SOLVED: To provide an overcurrent detecting circuit which can execute a simple and stable operation for detection of overcurrent. SOLUTION: Power supply of a power amplifier is switched over by power supply switching parts 41a and 41b in accordance with a level of an output signal SOUT. A voltage V23 is generated in a resistor 23 in accordance with collector current of a transistor 22 of the amplifier and supplied to the base of a transistor 25. At the time when the signal SOUT is absent, low-voltage power supply±VPL is selected by the switching parts 41a and 41b and a transistor 27 is turned off. When an overcurrent flows through the transistor 22, the transistor 25 is turned on, a signal Sp is outputted and thereby, operations of power supplying parts 16a and 16b are stopped. At the time when the signal SOUT is large, high-voltage power supply±VPH is selected and the transistor 27 is turned on. Even when the collector current becomes large and the voltage V23, is divided and becomes high, the transistor 25 is not turned on. Setting of a resistance value of the resistor 23 is simplified and also a stable operation of detection of the overcurrent can be executed.
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