Technical Descriptions (Power Supply) - Panasonic BL-PA100A Service Manual

BL-PA100A/BL-PA100KTA
5 Technical Descriptions
This power supply board uses the switching regulator method.
[Input Circuit]
The input current goes into the input rectifier circuit through both the fuse and the filter circuit. The filter circuit decreases the
noise voltage and the noise electric field strength.
[Rectifier Circuit]
The input current is rectified by D801 and D802 and charges C804 to make DC voltage. Then it supplies power to the converter
circuit.
[Converter & Control Circuit]
The following is an overview of how the power supply unit is controlled.
The control method of this power supply unit is pulse width modulation as Semi-Resonance Ringing Choke Converter.
When IC801 is ON, the energy is charged in the switching transformer primary coil according to Vin. When IC801 is OFF, the
energy is output from the secondary transfer as follows. Then the power is supplied to the Load. When IC801 is ON, power is
not output from the secondary side.
The output voltage is feed back in the IC801 according to the error detect circuit.
When Vin increase, IC801's on duty Ratio decrease. As a result, Charge of energy to the switching transformer primary coil
becomes the same as Low Vin, and Vout is kept constant.
When Iout increase, IC801's on duty Ratio increase. As a result, Charge of energy to the switching transformer primary coil
becomes the same as Low Vin, and Vout is kept constant.
C806 (Resonance Capacitor) is connect to IC801's #5pin-#7pin, rapid standup of flyback voltage is controlled.(Semi-Resonance
Ringing choke converter operation)
[Surge Absorber Circuit]
This circuit is for absorbing surge voltage generated by the transformer.
[Error detect Circuit]
The control circuit amplifies the output with increased voltage detected in the error detecting circuit.
In this power supply, the duty ratio is defined by changing the ON period of IC801.
This is shown as follows.
When the output voltage of the +10.5V circuit increases, the current of the photo coupler PC801 increases, the pulse width of
IC801 becomes narrower and the ON period of IC801 becomes shorter.
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