Reasons for insufficient output voltage of switching power supply
First, the load current is too large, the second is the low input voltage, and the third is the internal failure of the switching power supply. These three common reasons will lead to the problem of insufficient output voltage of the switching power supply.
1. The load current is too large
If the load is too large, it exceeds the load capacity of the switching power supply. The output power of the switching power supply is certain, such as 12V3A, and the output power is only 36W. If the load current is greater than 3A, the output voltage will be pulled down.
Disconnect the load and then measure the output voltage of the switching power supply. If the output is still abnormal, it is most likely the internal fault of the switching power supply; if the output is normal, connect the power supply in series with an ammeter to measure whether the load current is too large. If the load current is too large, it belongs to the switching power supply. If the output power is insufficient, it is necessary to replace the switching power supply with a larger output current.
If the output is normal before, it means that the back-end load has a short circuit and other faults, resulting in excessive load current. Or connect 4Ω power above 12W to simulate load test, if the output is normal, the switching power supply is no problem; if the output voltage is low, the internal fault of the switching power supply will reduce the load capacity.
Second, the input voltage is low
The input voltage range of the switching power supply is wide, generally about 100V~240V. Under normal circumstances, the input AC voltage will not be lower than 100V. This situation is rare. You can measure the input voltage. It may also be caused by faults such as poor line contact. Voltage is low.
3. Internal fault of switching power supply
The no-load output voltage is low or the no-load output voltage is normal. When the voltage is low when the 3A analog load is connected, it belongs to the internal circuit failure of the switching power supply.
The switching power supply generally has an electromagnetic interference filter circuit (EMI), a rectifier filter circuit, a power switch tube, a PWM controller circuit, a secondary side feedback circuit, overvoltage and undervoltage protection, and overcurrent and short circuit protection circuits.
The basic principle of switching power supply: first convert 220V alternating current into high voltage direct current through rectification, then convert PWM pulse width modulation into high frequency alternating current signal through power driver chip, switch tube, etc., output through high frequency transformer, and then rectify to obtain direct current voltage, Most of the switching power supply outputs will monitor the voltage in real time, and feedback through the optocoupler, which can be adjusted in real time when the voltage is high or low.
When the output voltage of the switching power supply is low, the common internal circuit faults are: deterioration of the Zener diode at the output feedback terminal (short circuit or low voltage regulator value, etc.), deterioration of the feedback resistor (such as R4 and R6 in the above figure); Tube failure; power driver chip failure (PWM controller circuit), rectifier diode failure, high-frequency transformer failure, etc.
Then, when looking for the failure cause of the switching power supply, it is necessary to measure and analyze step by step.
