Panasonic KX-FLB852CX Service Manual page 264

KX-FLB852CX / KX-FLB852CXS
[Surge Absorber Circuit]
This circuit is for absorbing surge voltage generated by the transformer.
[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
transistor.
In this power supply, the duty ratio is defined by changing the ON period of the main transistor.
This is shown as follows.
When the output voltage of the 24V circuit increases, the current of the photo coupler PC1 increases, the pulse width of the
output control IC becomes narrower and the ON period of Q1 becomes shorter.
[Over Current Limiter (O.C.L)]
The highest drain current of Q1 is limited by a limit current function of IC1. The 24V output is limited by this function.
[Over Voltage Circuit]
If the 24V output increases because the error detecting circuit or control circuit is broken, IC1 will recognize this signal and
output becomes 0V. D104, D275 and D503 also prevent over voltage.
[3.3V Output Circuit]
This circuit is composed of DC-DC converter method.
Dummy load method (to quickly check the power supply output)
Refer to POWER SUPPLY BOARD SECTION (P.193).
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