Protective Circuit Operation Section - Panasonic KX-NCP500GR Service Manual

4.6.5.

Protective Circuit Operation Section

Part 6 provides a description of the overvoltage/overheat protection circuits.
1. Abnormal State Detection Circuit
The abnormality detection circuit consists of the transistor Q520/Q521 thyristor circuits.
If power operation becomes abnormal and a signal is transmitted to the abnormality detection circuit, Q521 is turned on, cur-
rent flows to the diode of PC50 and is transmitted to the control circuit of the main converter, thereby shutting down main con-
verter operation. (See Part 2)
2. Overheat Protection Circuit
When temperature inside the power source rises to an abnormal temperature, the resistance of posister PTC540 rises, tran-
sistor Q540 is turned on, and the signalis transmitted to the abnormality detection circuit via D542.
3. Overvoltage Protection Circuit
If voltage of either 15V, 15VPT or 41V output becomes excessively high, the voltage is transmitted to the abnormality detec-
tion circuit via Zener diode D526.
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