Panasonic KX-FT937LA-B Service Manual page 47

KX-FT937LA-B
[Surge Absorber Circuit]
This circuit is for absorbing surge voltage generated by the Q1.
[Control Circuit and Detecting Circuit]
The control circuit amplifies the output with increased voltage detected in the error detecting circuit. Then it drives the main transis-
tor.
In this power supply, the oscillation frequency(f) of the main transistor is defined by changing the output load.
This is shown as follows.
When the output voltage of the 24V circuit increases, the current of the photo coupler PC101 increases, the pulse width of the out-
put control circuit becomes higher and the ON period of Q101 becomes shorter.
[Over Current Limiter (O.C.L)]
The highest drain current (Q1) is limited by controlling f of Q1 of 24V. The 24V output is limited by this circuit.
[Over Voltage Circuit]
If the 24V output increases because the error detecting circuit or control circuit is broken, output becomes 0V by turning on the
zener diode D105.
Dummy load method (to quickly check the power supply output)
Refer to Power Supply Board Section (P.45).
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