Analysis of common faults of switching power supply
In general, a blown fuse indicates that there is something wrong with the internal circuit of the power supply. Because the power supply works in the state of high voltage and high current, the fluctuation and surge of grid voltage will cause the current in the power supply to increase instantly and cause the fuse to blow. Emphasis should be placed on checking the rectifier diode, high-voltage filtering electrolytic capacitor and inverter power switch tube at the input end of the power supply, and checking whether there is any breakdown, open circuit and damage to this component. If the fuse is really blown, you should first check the components on the circuit board to see if the appearance of these components is burnt and the electrolyte overflows. If the above situation is not found, use a multimeter to measure whether the switch tube has a breakdown short circuit. Special attention should be paid to: Never switch on the machine directly after replacing a component when it is found to be damaged, so it is very likely that the replaced component will be damaged because other high-voltage components are still faulty. All high-voltage components in the above circuit must be inspected and measured before the fuse is completely eliminated. Humidity sensor probe, stainless steel electric heating tube PT100 sensor, cast aluminum heater, heating ring fluid solenoid valve.
No DC voltage output or unstable voltage output.
If the fuse is intact, there is no output of DC voltage at all levels under load. This situation is mainly caused by the following reasons: open circuit and short circuit in power supply, failure of overvoltage and overcurrent protection circuit, failure of auxiliary power supply, failure of oscillation circuit, overload of power supply, breakdown of rectifier diode in high-frequency rectifier filter circuit, leakage of filter capacitor, etc. After measuring the secondary components with multimeter, the breakdown of high-frequency rectifier diode and short circuit of load are eliminated. If the output is zero at this time, it is certain that the control circuit of power supply is out of order. If some voltage is output, it means that the front-stage circuit works normally, and the fault lies in the high-frequency rectifier and filter circuit. The high-frequency filter circuit mainly consists of rectifier diode and low-voltage filter capacitor, in which the breakdown of rectifier diode will make the circuit have no voltage output, and the leakage of filter capacitor will cause the output voltage to be unstable. The damaged components can be detected by measuring the corresponding components statically with a multimeter.
Poor load capacity of power supply
Poor load capacity of power supply is a common fault, which usually occurs in old-fashioned or long-working power supply. The main reasons are the aging of various components, the unstable operation of switch tubes, and the lack of timely heat dissipation. Should focus on checking whether the zener diode is heating and leaking, the rectifier diode is damaged, and the high-voltage filter capacitor is damaged.
