A Detailed Guide to Switching Power Supply Maintenance: Methods and Tips
Switching power supplies, which save materials, electricity, and high efficiency, have basically replaced traditional power supplies that rely on transformer transformation, diode rectification, and transistor stabilization. Due to the complexity of the switching power supply circuit, multiple protection circuits, and difficulty in maintenance, it is crucial for maintenance personnel to quickly troubleshoot the switching power supply. Proficiently mastering the basic components and working principles of the switching power supply is essential. Nowadays, most electronic instrument switch power supplies are mainly composed of electromagnetic interference filters, surge control circuits, rectification and filtering circuits, switch transformers, switch elements, pulse width modulation components and other components. Many switch power supplies have power factor correction circuits added between the rectification circuit and the filtering circuit to improve the power factor of the power supply, so that the current waveform of the power supply works in the same frequency and phase as the voltage wave, and the harmonic components in the current are eliminated as much as possible. The power factor of the switch power supply can reach 99%. The power factor correction circuit consists of switching devices and power factor correction modules.
1. When repairing a switch power supply, first use a multimeter to check whether each power component is broken down or short circuited, such as the power rectifier bridge stack, switch tube, and high-frequency high-power rectifier tube; Does the high-power resistor that suppresses surge current burn out. Re check whether the resistance of each output voltage port is abnormal. If the above components are damaged, they need to be replaced.
2. After completing the first step, if the power supply is not working properly, it is necessary to check the power factor module (PFC) and pulse width modulation component (PWM), consult relevant information, and familiarize oneself with the functions of each pin of the PFC and PWM modules and the necessary conditions for the modules to work properly.
3. Then, for power supplies with PFC circuits, it is necessary to measure whether the voltage at both ends of the filtering capacitor is around 380VDC. If there is a voltage of around 380VDC, it indicates that the PFC module is working properly. Next, the working status of the PWM component is checked, and the power input terminal VC and reference voltage output terminal VR are measured to start the control Vstart/VControl terminal voltage. Use a 220VAC/220VAC isolation transformer to supply power to the switching power supply. Use an oscilloscope to observe whether the waveform of the PWM module CT terminal to ground is a linear sawtooth wave or a triangle. For example, TL494 CT terminal is a sawtooth wave, and FA5310 CT terminal is a triangle wave. Is the waveform of output V0 an ordered narrow pulse signal.
