Main Board Section - Panasonic KX-MB2061CXB Service Manual

KX-MB2061CXB/KX-MB2061CX2/KX-MB2062CXB

6.19. Main Board Section

3.3V and 1.2V Power Supply descriptions
• IC800 is 2ch-output PWM type DC-DC converter controller, which make up step down type DC-DC converter circuit with Pch
power MOSFET Q802 and Q803, coil of L800 and L801, schottky diode of D800 and D803, capacitor of C800, C802 and C817,
C818.
The oscillation frequency in operation of this DC-DC converter is set to about 410kHz.
• R807,R809,R808,C814,R805,Q800,Q801 are UVLO (Under Voltage Lock Out) circuit.
Q801 turns on when the in-out voltage is about 16V or less and CS terminal becomes low so that IC800's operation is stopped.
• Q804,Q806,D805 and Q805,Q807,D806 are Clamp circuit which clamps VGS(Gate Voltage of Q802 and Q803) not to be a over
voltage.
• D801 and D804 are Zenner diodes which control not to be a over voltage at 3.3V and 1.2V output when ICs including IC800
break down.
5V Power Supply descriptions
• IC501 is turned ON when 3.3V power supply is booted , 5V is generated from 7V-input.
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