First, recently, when using a positive-to-negative voltage converter chip, I found that the output negative voltage was insufficient. When disconnected from the load, the voltage recovered, initially suspecting a problem with the downstream circuit. However, when using a regulated power supply, the negative voltage did not limit the current, and a multimeter test showed only 50mA. Later, I discovered that removing the large inductor connected in series in the positive output circuit of the chip resolved the issue. Therefore, in a 5V switching power supply, adding a large inductor to the input voltage supply circuit, while partially isolating the DC component, also affects the normal operation of the switching power supply.

Regarding usage issues, here are some common faults:

1. No DC voltage output or unstable voltage output

If the fuse is intact, there is no DC voltage output at any stage under load. This is mainly caused by the following reasons: open circuit or short circuit in the power supply; faulty overvoltage or overcurrent protection circuit; auxiliary power supply failure; oscillation circuit not working; excessive power supply load; rectifier diodes in the high-frequency rectifier and filter circuit broken down; leakage in the filter capacitor, etc.

2. Poor Power Supply Load Capacity

Poor power supply load capacity is a common fault, generally occurring in older or long-used power supplies. The main causes are aging components, unstable operation of the switching transistors, and insufficient heat dissipation. Focus on checking for overheating and leakage in the Zener diodes, damaged rectifier diodes, and damaged high-voltage filter capacitors.

3. Blown Fuse

Generally, a blown fuse indicates a problem with the power supply's internal circuitry. Since the power supply operates under high voltage and high current, fluctuations and surges in the mains voltage can cause a sudden increase in current within the power supply, leading to fuse blown. Focus on checking the rectifier diodes at the power input, the high-voltage filter electrolytic capacitors, and the inverter power switching transistors for breakdowns, open circuits, or damage.

While switching power supplies have high efficiency, they are not 100%. Furthermore, the thermal resistance of 12V switching power supply chips is relatively low, resulting in relatively poor heat dissipation. Therefore, it is essential to calculate the required voltage and current of the system to determine the system power consumption. Then, calculate the power consumption consumed by the switching power supply chip based on the efficiency curve. Use thermal resistance calculations to check if the chip temperature exceeds its tolerance level. Then, with a certain margin in mind, select the chip.