(1) Process problem of transformer
â‘ The service paint bake F is not in place, causing the burning core to be unstable, causing mechanical vibration and causing a slack:
â‘¡The length of the air gap is not suitable, which causes the T. working state of the claw changer to be unstable and make noise:
â‘¢If the wire package is not tightly wound, it may cause noise;
â‘ There is an air gap in the magnetic core combination, which causes air vibration at high frequency and makes a sound (if the transformer is fully vacuumed, it will generally not make a sound)
(2) The loop problem of the transformer
The loop problem of the transformer refers to that the loop of the transformer oscillates, which causes the change of the claw to occur.
â‘ Improper wiring of the circuit board, causing 1 disturbance to cause oscillation, resulting in noise:
â‘¡Improperly set the parameters of the feedback loop, causing the loop to become unstable and cause oscillation and noise:
â‘¢Quality problems of components in the loop, such as insufficient input filter capacitor capacity, poor quality of transmission and fast recovery diodes for rectification, poor quality of power MOS tubes, poor quality of high-voltage capacitors or diodes in the RCD recoil absorption loop, etc. These problems may cause vibration and cause noise.
(3) The core problem of the claw changer
When the transformer core is saturated, the current in the coil increases, the instrument heats up and produces self-excited oscillation, and the oscillation of the coil causes the surrounding air.
The vibration makes a noise.
(4) Load problem of switching power supply
①In the case of no load or light load, the switching power supply will oscillate at some T. operating points, which is manifested as the change of the instrument’s morphological call and the unstable output.
This phenomenon occurs because when the switch is under no-load/light-load, the instantaneous turn-on time of the switch is too long, which causes too much energy to be transmitted, and the voltage overshoot is also very large. It takes a long time to recover to the normal voltage, so the switch needs Stop this work for a period of time, so that the switch will be made by T. Work mode to make the changer vibrate at a lower frequency (regularly intermittent full-cut u!; frequency with drastic changes in period or duty cycle).
â‘¡Transformer T. is in a severe overload condition, and it can be burnt all the time. This is the origin of many power supplies that "scream" before they burn out.
Examples of abnormal noise of switching transformers and solutionsExample one
After the switching power supply is powered on, there is a hiccup sound, and the output DC voltage of each channel is extremely low and unstable. Check the load circuit first, and there is no damage to the components. Later, focus on testing the voltage absorption network connected in parallel with the N1 winding, and it feels that there is no abnormality. Take the oscillating board, replace the oscillating chip and peripheral circuits, and the fault remains after power-on. Note, there is no problem in the oscillation and voltage stabilization links, and there is no abnormality in rechecking the load circuit. Overhaul is in trouble.
Thinking of whether the switching transformer is broken? This possibility has to be ruled out first.
Connect DC18V directly to pins 7 and 5 of 3844, and connect DC100V to the DC530V power input end of the switching power supply. After power-on, the circuit starts to vibrate. After a while, Z101 in the circuit in Figure (c) starts to smoke. Observe that this circuit is a composite voltage absorption circuit. There is a resistance-capacitance absorption circuit in parallel at both ends of Z101. After temporarily removing Z101, measure the DC output voltage of each channel, and its level is proportional to the input voltage (the quality of the switching transformer at this time) It's self-explanatory).
At this point, the cause of the fault has become clear. Three 100V voltage regulator tubes are used in series instead of Z101. Power on and test the machine, and the switching power supply works normally.
Example two
1. The high-frequency transformer is the same as the iron core transformer, and the noise is caused by the tightness of the iron core. It's just that the frequency of the switching transformer is very high, so it emits a high-frequency "squeaking" sound.
2. Under normal circumstances, the squeaking noise from the switching power supply has little effect. If the sound is loud (the core is loose), it will cause heat. Press the magnetic core tightly and drop 502 instant glue.
Example three
When debugging the transformer, there should be no problem with the switching circuit. If the transformer sounds, it must be a problem with the transformer. The coil is not well wound, the ratio of the transformer primary to the secondary coil is inappropriate, the immersion insulating varnish is unqualified, and the magnetic core quality Problems, improper magnetic core air gap, etc. will cause transformer noise. To solve it is actually simple, mainly to check the dipping insulating varnish, the core air gap and the ratio of the transformer primary and secondary windings. If you still can’t solve this problem, please replace the magnetic core and try it out. When the air gap of the magnetic core is the same, the magnetic permeability of the magnetic core is different, which will cause the magnetic core to adapt to the switching frequency differently, which will naturally occur. ring.
Example four
The first category: If you have the conditions, you can separate the power supply circuit from the load, find a good switching power supply and connect the load. Check whether the whole circuit is working normally at this time. If the whole circuit is working normally at some time, then some of the problems are caused by the switching power supply on the original machine; if the new switching power supply transformer also affects the squeaking, it means that it is The load problem has nothing to do with the switching power supply on the original machine.
The second category: When it is determined that the switching power supply is causing the squeak, then focus on checking whether there is a short circuit in any place. I have also encountered many short-circuit faults that caused the squeak during maintenance. If there is no short circuit, please refer to the information on the maintenance of the switching power supply. There is much to say here, in short, only consider replacing the switching transformer later.
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