Reasons for low output voltage caused by switching power supply
1. Short circuit fault of switching power supply load
(Especially the DC/DC converter is short-circuited or has poor performance, etc.), at this time, first disconnect all the loads of the switching power supply circuit, and check whether the switching power supply circuit is faulty or the load circuit is faulty.
If the load circuit is disconnected and the voltage output is normal, the load is too heavy; or if it is still abnormal, the switching power supply circuit is faulty.
2. The failure of the filter capacitor or rectifier diode at the output voltage end is judged by the replacement method.
3. The performance of the switch tube is degraded, which causes the switch tube to fail to conduct normally, which increases the internal resistance of the switching power supply and reduces the load capacity.
4. The poor switching transformer will not only cause the output voltage to drop, but also cause insufficient excitation of the switch tube and damage the switch tube.
5. The 300V filter capacitor is not good, resulting in poor load capacity of the switching power supply, and the output voltage will drop as soon as the load is connected.
6. Insurance burns out or blows up
Mainly check the rectifier bridge, diodes, switch tubes and large filter capacitors on 300 volts. It may cause the fuse to burn and become black, or it may be caused by a problem with the anti-jamming circuit.
Note: The fuse is burned due to the breakdown of the switch tube, which usually burns the switching power supply control chip and the current detection resistor, and the thermistor is easier to burn out together with the fuse.
7. The output voltage is too high
The high output voltage generally comes from the voltage-stabilizing sampling and voltage-stabilizing control circuits.
In the closed control loop composed of DC output, sampling resistor, error sampling amplifier such as TL431, optocoupler, power control chip and other circuits, any problem in any of these parts will cause the output voltage of the switching power supply to rise.
8. The fuse is normal, no output voltage
The fuse is normal and no output voltage indicates that the switching power supply is not working or has entered a protection state. The first step is to check the value of the start-up voltage of the start-up pin of the power control chip. If there is no start-up voltage or the start-up voltage is too low, check whether the external components of the start-up pin and the start-up resistor are leaking.
If the switching power supply control chip is normal, the fault can be quickly found through the above monitoring. If there is a start-up voltage, measure whether there is a jump between high and low levels at the output end of the control chip at the moment of booting. If there is no jump, it means that the control chip is damaged, the peripheral oscillation circuit components are damaged or the protection circuit is faulty. Chip, check peripheral components, check one by one; if it is jumping, in most cases, the switch tube is bad or damaged.
The above are the main reasons for the low output voltage of the switching power supply. I hope it will be helpful to everyone.
