Switching power supply maintenance tips

With the rapid development of power science and technology, electronic equipment refined, high-end, the requirements for power supply are becoming more and more stringent, so the switching power supply that can be used to stabilize the power output is also more and more widely used, but the ensuing failure of various power switches1. Switching power supply maintenance steps

(1) When repairing the switching power supply, first use a multimeter to detect whether the power components are broken down short circuit, such as the power rectifier bridge stack, the high-frequency high-power rectifier tube of the switching tube; Whether the high power resistance to suppress the long inrush current is burned out. Then check whether the resistance of each output voltage port is abnormal. If the components are damaged, replace them.

(2) After the first step is completed, it cannot work normally after the power supply is passed, and then it is necessary to detect the power factor module and pulse width modulation component, consult the relevant information, and be familiar with the function of each foot of the PFC and PWM module and the necessary conditions for the normal operation of the module.

(3) Then for the power supply with PFC circuit, it is necessary to measure whether the voltage at both ends of the filter capacitor is about 380VDC, if there is about 380VDC voltage, it indicates that the PFC template works normally, and then detect the working status of the PWM component. Measure the power input end VC, reference voltage output end VR, start control Vstart/Vcontrol end voltage is normal, use the 220VAC/220VAC isolation transformer to supply power to the switching power supply, use the oscilloscope to observe whether the PWM template CT end to the ground waveform is a good linear sawtooth wave or triangle. For example, the TL494 end is sawtooth wave, the CT end of FA5310 is triangular wave, and the waveform of the output end V0 is an ordered narrow pulse model.

(4) In the practice of switching power supply maintenance, many switching power supplies use UC38XX series 8-pin PWM components, and most power supplies cannot work because the power supply starting resistance is damaged, or the chip performance is reduced. When R breaks the VC, the PWM component cannot work, and the resistor with the same power resistance value as the original needs to be replaced. When the starting current of the PWM component is increased, the R-value can be reduced until the PWM component can work normally.

In short, the switching power supply circuit is easy and difficult, the power is large and small, and the output voltage is diverse. As long as you grasp its core things, that is, fully familiar with the basic structure of the switching power supply and the characteristics of PFC and PWM modules, the basic conditions of their work, according to the above steps and methods, more manual maintenance of the switching power supply, you can quickly eliminate the switching power supply failure, to achieve the effect of twice the result with half the effort.

Two, switching power supply maintenance skills

After talking about the switching power supply maintenance steps above, we will next talk about what skills can be used in the maintenance of the switching power supply: in the case of power failure, "see, smell, ask, quantity"

Look: Open the shell of the power supply, check whether the fuse is blown, and then observe the internal situation of the power supply, if the PC board of the power supply is found to have burnt or broken components, you should focus on checking the components and related circuit components here.

Smell: Smell the inside of the power supply to see if there is a mushy smell, and check whether there are burnt components.

Q: Ask the power supply damage process, whether the power supply is illegal operation.

Quantity: Before no power, use a multimeter to measure the voltage at both ends of the high-voltage capacitor. If the switching power supply does not vibrate or the switch tube is open caused by the fault, in most cases, the high-voltage filter capacitor charging, the resistance value should not be too low, otherwise there may be a short circuit inside the power supply. Capacitors should be able to charge and discharge. Remove the load and measure the resistance to the ground at the output end of each group respectively. When normal, the watch hand should have capacitor charge and discharge oscillation, and the last indication should be the resistance value of the drain resistance of the path.

After power on, observe whether the power supply has burning insurance and individual components smoke phenomenon, if there is to cut off the power supply in time for maintenance. Measure whether there is 300 volts output at both ends of the high-voltage filter capacitor, if not, focus on checking the rectifier diode, filter capacitor, etc. Measure whether the secondary coil of the high-frequency transformer has output, if not, it should focus on checking the rectifier diode, filter capacitor, three-way voltage regulator on each output side.

如果电源启动一下就停止，则该电源处于保护状态下，可直接测量PWM芯片保护输入脚的电压，如果电压超出规定值，则说明电源处于保护状态下，应重点检查产生保护的原因。

12V开关电源原理讲解                

 该开关电源属于小功率开关电源，输入220V交流市电，输出12V直流1.3A, 主要应用于小型设备的供电，比如楼宇监控设备等。其控制核心器件为脉宽调制集成电路TL3843P(内含振荡器，脉宽调制比较器，逻辑控制器，具有过流，欠压等保护控制功能，最高工作频率可达500MHZ,启动电流仅需LMA)。各引脚功能如下：（1）脚是内部误差放大器的输出端，通常（2）脚之间有反馈网络，确定误差放大器的增益。（2）脚是反馈电压输入端，作为内部误差放大器的反相输入端，与同相输入端的基准电压（+2.5V)进行比较，产生误差控制电压，控制脉冲宽度。(6)脚过流检测输入端，当接人的电压高于1V时，禁止驱动脉冲的输出。（4）脚为RT/RC定时电阻和电容的公共接人端，用于产生锯齿振荡波。（5）脚为接地端。（6）脚为脉宽可调脉冲输出端。（7）脚为工作电压输入端。（8）脚为内部基准电压（VREF=5V）输出端。