Switching power supplies play a crucial role in modern electronic devices. Their high efficiency, miniaturization, lightweight design, and high reliability make them widely used in various fields. However, sometimes switching power supplies may experience a lack of output, which can affect the operation of electronic devices. Therefore, we need to understand the possible causes of no output from a switching power supply in order to take timely measures to resolve the problem.
Abnormal input voltage is a common cause of no output from a switching power supply. If the input voltage is too low or too high, the switching power supply may not function properly, resulting in no output. In this case, it is necessary to check whether the input voltage is within the rated range. If there is an abnormality, appropriate measures should be taken to adjust it.
Excessive load can also be one of the reasons why a switching power supply has no output. When the load exceeds the rated output capacity of the switching power supply, it may fail to function properly, resulting in no output. In this case, it is necessary to reduce the load or replace it with a switching power supply with one of higher wattage.
Malfunctioning protection circuits can also cause a switching power supply to have no output. For example, overcurrent protection, overvoltage protection, and overheat protection circuits may shut down the power output if they malfunction. In this case, it is necessary to check whether the settings and functions of the protection circuit are normal. If any abnormalities are found, they should be adjusted or repaired.
Failure of internal components in the switching power supply can also be a cause of no output. For example, components such as the switching transistor, rectifier diode, and filter capacitor may be damaged due to aging or burnout, causing the switching power supply to malfunction. In this case, it is necessary to check whether the internal components of the switching power supply are functioning properly, and if any are damaged, they should be replaced.
Circuit board failure can also cause a switching power supply to have no output. For example, poor soldering, component damage, or circuit board corrosion can all lead to circuit board failure, thus affecting the normal operation of the switching power supply. In this case, it is necessary to check whether the circuit board is functioning properly; if faulty, it needs to be repaired or replaced. There are many reasons why a switching power supply may have no output, requiring analysis and troubleshooting based on the specific situation. During troubleshooting, the following steps can be taken: input voltage, load, protection circuit, components, and circuit board, to promptly identify the problem and take appropriate measures to resolve it.
The troubleshooting steps for a switching power supply with no output are as follows:
1. Check the power plug and power cord to ensure they are properly connected and not loose or damaged.
2. Check if the power switch is in the on position. If the power switch is in the off position, the switching power supply will of course have no output.
3. Check the power supply load. Disconnect the power supply load and check if the power supply's output voltage and current are normal. If the power supply works normally, the power supply failure is likely due to a load fault.
4. Check if the fuse is damaged. If the fuse is blown, it means that there is a fault in the power supply circuit.
5. Inspect the internal components of the power supply, such as capacitors, diodes, transistors, and integrated circuits. If the above troubleshooting methods fail to resolve the issue, further disassembly of the power supply is necessary for inspection. During the troubleshooting process, exercise caution to avoid electric shock and damage to the power supply.
6. Observe whether there is voltage output at each output terminal of the switching power supply. If there is voltage output, further check whether the collector voltage of the switching transistor is 0 or lower than 1.4 times the mains voltage. If so, the AC 220V input circuit and rectifier filter circuit need to be checked.
7. If the collector voltage of the switching transistor is normal, then the base voltage of the switching transistor needs to be checked. Alternatively, at the moment of power-off, use an analog multimeter set to the R x 1 ohm range, with the black probe connected to the base and the red probe connected to the negative terminal (hot ground) of the rectifier filter capacitor. If you hear a startup sound from the power supply, it indicates that the power supply oscillation circuit is normal, but there is a lack of startup voltage. This could be due to an open circuit or a broken copper foil in the startup resistor.
8. If there is no start-up sound, after measuring the base-emitter junction, quickly switch the meter to the voltage range and measure whether the collector voltage is rapidly discharged.
