LG GR-K20SVZ Technical Manual page 20

MICOM Function and Description of Circuit
2. Description of Circuit
1) Power circuit
The power circuit consists of the noise attenuation part and the SMPS (switch mode power supply)
part. The SMPS consists of the rectifier (BD1 & CE1) to convert AC voltage to DC voltage, switching
part (IC2) to switch the converted DC voltage, transformer to transmit energy of the first side of the
switching end to the second side, the secondary power to supply power to MICOM and IC, and the
feedback part (IC3, ZD1) to feedback the secondary voltage to the first side of transformer in order to
maintain the secondary voltage constant.
: High voltage (310 V ) is maintained in this circuit. Wait at least 3 minutes after
Caution
dc
unplugging to allow the current to dissipate. There is a danger of electric shock.
2) Oscillation circuit
The oscillation circuit provides the clock signal for synchronization and calculation of time in relation
to the logic elements of microprocessor IC 1. OSC 1 must always use the original rated parts,
because if the specification changes, the timing generated will not be correct, causing erratic
functioning of the microprocessor.
3) Reset circuit
The reset circuit allows the entire process to be started from the initial status by resetting the
microprocessor whenever power is applied to it at pin 29. LOW voltage is applied to the reset
terminal for 10 ms at the beginning of power input. The reset terminal has a voltage of 5 Vdc during
general operation. If the reset operation fails, the microprocessor will not operate.
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