I. How to troubleshoot switching power supply faults
1. Short-circuit method
Parallel switching power supplies generally use direct sampling voltage regulation control circuits with optocouplers. When the output voltage is high, the short-circuit method can be used to distinguish the fault range.
The short-circuit troubleshooting process is as follows: First, short-circuit the two pins of the photosensitive receiver tube of the optocoupler. This is equivalent to reducing the internal resistance of the photosensitive receiver tube. If the main voltage still does not change, it indicates that the fault is after the optocoupler (on the primary circuit side of the switching transformer). Conversely, the fault is in the circuit before the optocoupler.
It should be noted that the short-circuit method should be performed selectively and only after familiarity with the circuit; blind short-circuiting should be avoided to prevent exacerbating the fault. Furthermore, from a safety perspective during maintenance, the load circuit should be disconnected before short-circuiting.
2. Series bulb method
The so-called series bulb method involves removing the fuse from the input circuit and connecting a 60W/220V light bulb in series across the fuse. When AC power is applied, if the bulb is very bright, it indicates a short circuit. Because the bulb has a certain resistance (approximately 500Ω for a 60W/220V bulb, referring to thermal resistance), it acts as a current limiter. This allows for a direct assessment of the circuit fault by observing the bulb's brightness; furthermore, the bulb's current-limiting effect prevents immediate damage to components in the short-circuited circuit. Once the short circuit is cleared, the bulb's brightness will naturally decrease. Finally, the bulb can be removed and the fuse replaced.
II. What are the load testing methods for switching power supplies?
1. Proportional Load Adjustment: This method involves continuously adjusting the load resistance to gradually increase the power supply's output current according to a predetermined ratio. By recording the voltage and current values under different loads, the output characteristic curve of the switching power supply can be plotted. This method is very helpful in evaluating the stability and load capacity of the switching power supply. 2. Transient Response Test: This test method is used to evaluate the response speed and stability of the switching power supply under load changes. By suddenly changing the load on the switching power supply, the transient response of the power supply's output voltage is observed. Generally, load change tests include short circuit, open circuit, and positive load jump. This test method is very important for evaluating the transient response performance of the switching power supply. 3. Efficiency Test: The efficiency of a switching power supply is an important performance indicator, affecting its energy consumption and thermal management. The efficiency test measures the input and output power of the switching power supply and then calculates the power supply's conversion efficiency. This test method helps evaluate the power utilization rate of the switching power supply and the efficiency changes under different load conditions. 4. Peak Power Test: Switching power supplies usually need to provide additional power for a certain period of time to meet the peak demand when devices start up. The peak power test ensures that the switching power supply can stably output additional power for a short period of time. The testing method generally involves increasing the load over a specific time period and recording the output voltage and current waveforms of the switching power supply. 5. Temperature Testing: The temperature of a switching power supply has a significant impact on its performance and lifespan. Temperature testing involves running the switching power supply under load conditions for an extended period and recording the temperature changes. This test method can evaluate the switching power supply's heat dissipation design and its stability in high-temperature environments.
