I. Reasons for Low Output Voltage of Switching Power Supply
A switching power supply uses electronic switching devices and a control circuit to continuously "turn on" and "turn off" the electronic switching devices, allowing the electronic switching devices to pulse-modulate the input voltage, and then complete the voltage conversion and regulation.
If the output voltage of the switching power supply is lower than the nominal voltage during practical operation, there are several possibilities:
(1) If the switching power supply of the new device exhibits this condition, it may be due to insufficient output power. The selected power supply should have sufficient power margin to prevent "underpowered power supply"; it may also be that the power supply output does not meet the design target, which is a quality issue with the product itself. In addition, the output power will decrease at high temperatures, so it should be derated. Generally, manufacturers will provide output characteristic curves at different temperatures.
(2) The 220V AC voltage input and the rectifier filter circuit cannot supply the operating voltage to the switching transistor, which exceeds the control range of the pulse width adjustment circuit.
(3) Overcurrent in the load circuit causes the load on the switching power supply to increase, resulting in a drop in output voltage.
(4) The original power supply output suddenly drops. First, check if the load has changed. If the load is normal, it is very likely that the internal components are damaged. If possible, you can check the product's switching devices for damage; otherwise, you will have to send it for repair or replacement.
(5) Power-on/power-off switching error: The power supply is in standby mode the instant the horizontal scanning circuit starts working. This type of defect applies to machines without a backup power supply, where the CPU power supply is taken from the same power supply and is not supplied by an auxiliary power supply.
(6) The power on/off interface circuit ends due to a defect and is in a state between power on and standby, which causes the output voltage of the switching power supply to be lower than the normal value and higher than the standby value.
(7) When the maintenance circuit is terminated, it enters the conduction state due to a defect, causing the power supply to enter the weak vibration state, which causes the output voltage of the switching power supply to drop.
(8) Damage to diodes, filter capacitors, and current-limiting resistors in the rectifier output circuit causes low output voltage.
(9) The disadvantage of the pulse width modulation circuit is that it cannot respond correctly to changes in the output voltage of the switching power supply, and the adjustment direction of the base voltage of the switching transistor is incorrect, which results in a low output voltage of the switching power supply.
(10) Changes in the positive feedback resistor value in the positive feedback circuit, deterioration of the freewheeling diode function or defects in the constant current source can lead to a lack of positive feedback, resulting in a longer oscillation period and a decrease in oscillation frequency, which in turn causes a low output voltage of the switching power supply.
(11) The self-excited switching power supply operates at a low frequency because it does not receive the retrace pulse, resulting in a low output voltage.
(12) The output filter capacitor or rectifier diode is faulty (the filter capacitor may be bulging or leaking, etc. Bulging can be seen directly, while leakage or a faulty diode requires testing with a multimeter or replacement).
II. Solutions for Low Output Voltage of Switching Power Supply
Through the above introduction, you should now understand the possible causes of low output voltage in switching power supplies. So, how do we resolve this situation when we encounter a low output voltage in a switching power supply?
What should be done when the output voltage of a switching power supply is too low? Here are some common solutions for your reference:
1. Check the mains voltage.
If the mains voltage is unstable, it is recommended to add a voltage regulator or use a more stable mains power supply.
2. Check the capacitors or transformer.
If a fault is found in the capacitor or transformer itself, it should be replaced promptly.
3. Replace the switching transistor
If the switching transistor fails, it needs to be replaced with a new one.
4. Adjust the internal parameters of the switching power supply
Switching power supplies have multiple internal parameters, and the output voltage can be adjusted by regulating these parameters.
in conclusion:
Low output voltage from a switching power supply can be caused by a variety of reasons. Each possibility should be carefully checked and eliminated, and the appropriate solution should be selected based on the specific situation. By repairing the switching power supply according to the methods described above, the problem of low output voltage can be effectively resolved, ensuring the stability and reliability of the equipment.
