Samsung LW32A23W, Руководство по обслуживанию

Страница: 9 / 39

Block Diagrams
LW32A23W/LW40A23W
Resonance Circuit (Power Source for Inverter)
Operating Principles
Explains the circuit of the power source for the inverter. With the operation of the MULTI block, a voltage is
generated in the ancillary windings (4-5Pin) of T804S and is applied to 1 Pin (Vcc terminal) of the resonance
circuit to start oscillation. High side FET (Q4) and low side FET (Q5) are turned on alternately, delivering
energy to the secondary circuit. For voltage regulation, the output voltage is divided along resistors and
monitored by the transistor (QI809), and the photo coupler (PC801S) is turned on or off. If the output ,
voltage rises, PC801S is turned on and draws current from 13 Pin of the resonance circuit. The switching
frequency then increases, reducing the charge period of the resonance condenser (CI811) and thereby
limiting the output voltage. On the other hand , if the output voltage decreases, no current is drawn from
13 Pin of the resonance circuit and the switching frequency decreases, extending the charge period of the
resonance condenser and thereby raising the output voltage.
Protections
1. Overvoltage
The output voltage is divided along the resistors and monitored by QI810. If the output voltage rises, the
QI810 voltage also rises, which triggers QO810 to turn PC802S on. This will increase the voltage at 5 Pin
of the resonance IC, which stops oscillation in the latch mode.
2. Overcurrent
The current flowing in the resonance condenser (CI811) is divided through CI808, converted into voltage
at the resistors (RI809, RI816) and is monitored by 3 Pin of theresonance IC. If the output current rises,
the current in the primary winding wire also rises, which triggers the voltage at 3 Pin of the IC to rise as
well. If the voltage exceeds the set value, the pulse width is narrowed to limit the current.
3. Thermal Shutdown
The resonance IC has a built-in thermal shutdown function and stops oscillation at over 125 ˚C
FET VDS Waveform of the resonance circuit