Judgment of short circuit between turns of switching power transformer:
1. Weld two leads on the high-frequency low-voltage output side of the switching power transformer with a 12-volt switching power supply (that is, before entering the rectification filter), and then string a 12V2W small bulb on the high-frequency output side without rectification filter into the secondary low-voltage side of the switching transformer to be tested If the light bulb is slightly red and not bright after access, but the short-circuit test transformer is bright after any winding, it proves that the switching transformer is good, and if the light bulb is bright after access without short circuit winding, it proves that the switching transformer has an inter-turn short circuit.
2, the primary winding of the switching transformer string a 10 micromethod capacitor and then the winding after the string of capacitors into the capacitance measuring end of the digital multimeter, hit the capacitance measuring gear to measure the capacitance capacity, and then the output end of the switching transformer any winding short-circuit capacity, if the two measurements of the multimeter display the same number or little difference, can be judged as transformer short circuit. If the difference between two measurements is large, the transformer is normal.
In the case of checking the winding resistance or the path, there are four ways to judge the quality of the switching transformer:
1, substitution method, with a good transformer replacement test. Or with the suspicion of bad, installed on other circuits to test, get a judgment;
2, with voltage/current instantaneous detection, measure two transformers at the same time, compare the detection data. In the secondary winding, the 1.5V battery is connected instantaneously to measure the short-circuit current value of the primary winding. If the induced current value is seriously small, the transformer is bad.
3, transform the two measurement methods, such as 2 method, measured the induced current value, and then through a turn of short-circuit wire, measurement once, two measurement results are similar, judge the transformer has been broken. If the second measurement value is seriously small, it means that the transformer is good.
4, use voltage ringing method to test good or bad. Need a kHz signal generator and an oscilloscope, with measurement, see its attenuation waveform, if during the pulse flat top, the oscillation quickly attenuated, indicating that the transformer has been broken. The opposite is good. The tester needs to have a certain amount of experience and have a good idea of the waveform.
The four detection methods are all based on the principle that the electromagnetic induction capacity (inductance characteristic) deteriorates after the short-circuit between turns of the transformer.
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Post time: Nov-16-2024