Operating Sequence - LG LMC1575BD Service Manual

OPERATING SEQUENCE

The following is a description of component functions during oven operation.
1. Inverter power supply circuit.
The inverter power supply circuit powered from the line voltage, 120 V~ 60 Hz
AC input supplies 4000 V DC to the magnetron. and functions in placed of the
H.V transformer, the H.V capacitor , and H.V diode.
1. The AC input voltage 120 V~ 60 Hz is rectified to DC voltage immediately.
2. DC voltage will be supplied to the switching devices called IGBT. These
devices are switched ON-OFF by the 24 to 70 kHz PWM (pulse width
modulation) signal from the microcomputer in the DPC.
3. This drives the High voltage transformer to increase voltage up to 2000 V AC.
4. Then the half-wave doubler voltage rectifier circuit, consisting of the H.V.
diodes and capacitors, generates the necessary 4000 V DC needed for the
magnetron.
5. Consumption power is always monitored by the signal output from the current
transformer built into the inverter circuit.
6. This signal is fed back to the microcomputer in the DPC to determine
operating conditions and output necessary to control PWM signal to the
Inverter Power Supply for control of the output power.
2. Power output reduction.(Normal condition)
1. In 100%, 90% and 80% power levels, output power will gradually be reduced
to avoid overheating.
1-1. for example of 100% power,
After about 1 minute, the output power will be reduced to 90%.
1-2. and then the output power will be reduced from 90% to 70% for
6minutes gradually.
1-3. and then 70% will be kept on.
2. If the power level starts at 90%, the level will be kept till 1minute and then
reduced to 70% gradually.
3. Power output reduction.
(Continues using condition)
Continues using make inverter overheating. To protect inverter PCB from
overheating, Inverter detect temperature itself.
1. If you restart product within 15 minutes from the end of working, the power
consumption is the same power consumption of the end of working.
2. If you unplug the power cord and then you plug the power cord, the power
consumption is max power.
4. Variable power cooking control
High Voltage Inverter Power Supply controls output power by the signal from
Digital Programmer Circuit. Power relay always stay on, but PWM (Pulse Width
Modulation) signal controls microwave output power
Power Level
High * Boiling water.
(100 %) * Browning ground beef.
* Making candy.
* Cooking poultry pieces, fish, & vegetables.
* Cooking tender cuts of meat.
90 *Reheating rice, pasta, & vegetables.
80 * Reheating prepared foods quickly.
* Reheating sandwiches.
70 * Cooking egg, milk and cheese dishes.
* Melting chocolate.
60 * Cooking veal.
* Cooking whole fish.
* Cooking puddings and custard.
50 * Cooking ham, whole poultry and lamb.
* Cooking rib roast and sirloin tip.
40 * Thawing meat, poultry and seafood.
30 * Cooking less tender cuts of meat.
* Cooking pork chops and roast.
20 * Taking chill out of fruit.
* Softening butter.
10 * Keeping casseroles and main dishes warm.
* Softening butter and cream cheese.
4-3
Use