What is the high voltage power transformer in the microwave oven and how to detect it?

1.High voltage transformer is a special magnetic leakage transformer. The high voltage transformer usually has 3 windings, one winding, the AC 220V  electric voltage applied in this winding, the secondary magnetron filament winding output communication 3. 3V of the filament voltage, the two high voltage winding output AC 2100V high pressure, and some fourth windings, that is the power adjustment winding. A plurality of silicon steel sheets with a certain thickness are inserted between one and two windings to form a magnetic shunt with high reluctance gap in the transformer. When the high voltage transformer works, a certain amount of leakage flux will be produced in the magnetic shunt circuit, which controls the output current of the transformer and keeps the working current of the magnetron relatively stable.

When magnetron operates, there is oscillating current in the two side high voltage winding of the transformer, resulting in magnetic saturation of the iron core nearby. Assuming that the magnetron's anode voltage rises and the anode current increases because of the city's electric wave action, the current of the two side windings of the transformer increases, making the magnetic saturation deepened and the leakage flux increasing, which makes the two side high voltage of the transformer down, that is, the anode voltage of the magnetron is reduced, the anode current falls, and vice versa. Therefore, it can automatically adjust the anode voltage and current and stabilize the output power of the microwave.

High voltage transformers mainly rely on leakage flux to keep the magnetron working current stable, so it is also known as magnetic flux leakage transformer. This transformer can maintain the stability of the magnetron anode current under the wide fluctuation range of the power supply, and has been widely applied in the microwave oven. In addition to special products, almost all microwave ovens use such transformers.

2.Detect the high voltage power transformer of the microwave

The RX1 gear is used to measure the cold resistance of the transformer. The secondary winding is usually a few ohms; if it is too small, there may be inter turn short circuit. The two side high voltage winding is from ten to hundreds of ohms. If it is infinite, it will be cut off; if it is small, the partial short circuit between the turns will be close; the filament winding will be close to o ohm.

Mega ohmmeter (500V insulation resistance meter) or multimeter RX10 1000 ohm gear are used to measure the resistance of the primary and secondary sides to the outer shell of the transformer is larger than two megaohms. If any resistance is too small, it means that the transformer is creepage, and the insulation is bad. When measuring, we should pay attention to removing the insulating paint film on the tested parts of the transformer shell, so as to ensure the contact between the pen and the shell is good. At the same time, do not touch hands with the pen and contact with the measuring point of the conductive parts, otherwise the needle may indicate a smaller resistance. We should pay attention to this when we use multimeter to measure high-voltage capacitors and high voltage diodes.

When detecting the transformer, the lead should be disconnected and retested (for example, one end of the high voltage winding will be grounded with the core and chassis), otherwise it will be misjudged. In addition, the high voltage capacitor connected to the winding should be discharged before the test to avoid electric shock.

The main common faults of the high voltage transformer are as follows.

(1) the winding or lead line is broken and the contact is bad. This makes the microwave oven unheated or unstable. First check the lead and plug in the case, if the broken line, as long as the re welding or connection is reliable, if the contact is bad, should clear the dirt, and strengthen the contact fastness of the two.

 (2) Partial short circuit inside the high voltage winding, leakage or short circuit between the windings and the housing. This will cause the microwave oven to not work, fuse or work unstable. First roasting or rewinding, if it can not be solved after baking, or it can not be rewound, it needs to be replaced.

This article is from Allicdata Electronics Limited.