Sanyo SM-GA0005 service manual 2.1HIGH VOLTAGE RECTIFYING CIRCUIT

K Stands for a constant

E Stands for the microwave frequency. f Stands for the microwave frequency.

tgδ Stands for loss angle tangent of the heated matter.

Er Stands for relative dielectric constant of the heated matter.

2. THE STRUCTURE AND WORKING PRINCIPLE OF MICROWWAVE OVEN.

Microwave oven can be classified to many kinds

according to various construction, volume and control function. But anyhow, the main electric parts are all 120V

composed of high voltage rectification, cooling system. Microwave generator, electric control system and heating chamber (FIG.2-1). Its working process are as follows: 120V power frequency voltage transferred to the rectifier through electric control system, and then be changed to 4000V direct volt-age by the rectifier, and be then transferred to the microwave generator, the generator stars working to transfer the microwave energy to the heating chamber for heating food through wave guide tube. At the same time, the electric control system set off the cooling system to cool the working rectifier and the microwave generator to keep the oven working steadily from a too high temperature. If

something wrong with the cooling system cause the temperature too high, the control system would cut off the power automatically to prevent microwave generator being damaged form the high temperature. Now, we’d like to introduce the working principle of each part of the widely used model, mechanical control and touch control microwave oven.

2.1HIGH VOLTAGE RECTIFYING CIRCUIT.

At present, home use microwave oven adopt this high voltage rectifying circuit as shown at diagram 2-2.The circuit is a single phase, semi-wave, double voltage rectifying circuit. The circuit has only a high voltage capacitor, a high voltage diode, a magnetic leakage transformer besides the magnetron, is very simple.

The working principle of the circuit: 120V power boosted through the transformer, output about 2000V alternating high voltage current when the high voltage winding is at the positive half-circle, the high voltage winding is at the negative half-circle, the diode is cut off and the magnetron is conducted. The electricity charged at the positive half-circle of the capacitor is series connected with the positive phase of the winding voltage, and got a doubled, about 4000V direct high voltage, then transferred to between the cathode and the anode of the magnetron.

120V

120V

Fig.2-2 Fig.2-3

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