UPS power supply common failure analysis and maintenance skills (I)

Problem 1: UPS power supply output normal when there is utility, no utility buzzer beeping, no output

Failure analysis: judging from the phenomenon of the battery and inverter part of the failure

Solution ideas: 1, check the battery voltage to see if the battery is undercharged, if the battery is undercharged, check whether the battery itself is a fault or charging circuit failure.

2, if the battery working voltage is normal, check whether the inverter drive circuit is working normally, if the drive circuit output is normal, it means the inverter is damaged.

3, if the inverter drive circuit does not work normally, check whether the waveform generation circuit has PWM control signal output, if there is control signal output, it means the fault is in the inverter drive circuit.

4、If the waveform generation circuit has no PWM control signal output, check whether the output is blocked by the protection circuit work, if so, identify the reason for protection;

5, if the protection circuit does not work and the working voltage is normal, and the waveform generation circuit does not have PWM waveform output, it means that the waveform generation circuit is damaged.

Problem 2: Inverter power stage a pair of amplifier transistor damage, replace the same type of transistor, after a period of operation and burned

Failure analysis: the current is too large

Solution: 1, overcurrent protection failure. When the inverter output overcurrent, overcurrent protection circuit does not work;

2, pulse width modulation (PWM) component failure, the output of the two complementary waveform is not symmetrical, a long conduction time, while the other conduction time is short, so that the two arms work unbalanced, or even two arms on at the same time, resulting in damage to the two tubes;

3, the power tube parameters differ greatly, even if the input symmetric waveform, the output will be asymmetric, the waveform by the output transformer, resulting in bias, that is, the flux is not balanced, the accumulation of transformer saturation and current surge, burned power tubes, and a burned, the other one also burned.