On the cause of switching power transformer ringing(1) Technological problems of transformer The in-service paint baking f is not in place, resulting in loose combustion core and mechanical vibration:
The length of air gap is not suitable, resulting in unstable T. operation state of claw changer and sound: If the wire package is not wound tightly, it may also cause noise; There is an air gap in the magnetic core assembly, which causes air vibration and makes a sound at high frequency (generally, the transformer will not make a sound if it is fully switched on through vacuum)
(2) Loop problem of transformerThe loop problem of transformer means that the loop of transformer oscillates, which causes the claw converter to vibrate. Improper wiring of the circuit board causes 1 disturbance and oscillation, resulting in sound:
Improper setting of feedback loop parameters leads to loop instability, resulting in oscillation and sound: Quality problems of element devices in the loop, such as insufficient input filter capacitor capacity, fast recovery diode quality of transmission rectifier, poor quality of power MOS tube, poor quality of high-voltage capacitor or diode of RCD recoil absorption circuit, etc. these problems may lead to vibration and sound.(3) Iron core problem of claw changer
When the transformer core is saturated, the current in the coil increases, the transformer instrument generates heat and generates self-excited oscillation. The oscillation of the coil causes the surrounding air,It vibrates and makes a sound.(4) Load problem of switching power supply
In the case of no-load or light load, the switching power supply will oscillate at some T. operating points, which is characterized by the noise of the variable instrument and the instability of the output.This phenomenon occurs because the instantaneous opening time of the switch is too long during no-load / light load, resulting in too much power transmission, and then a large voltage overshoot. It takes a long time to recover to the normal power supply. Therefore, the switch needs to stop this work for a period of time, so that the switch can work in time. As a mode, the converter vibrates at a lower frequency (regular intermittent total cut-off u!; the frequency of sharp change in cycle or duty cycle). Transformer T. in a serious overload state, it can be burned at any time. This is the origin of "scream" before many power supplies are burned.
Abnormal noise of switching transformer and its solution exampleExample 1
After the switching power supply is powered on, there is a hiccup sound. The measured output DC voltage of each circuit is very low and unstable. Check the load circuit first, and there are no damaged components. Later, the voltage absorption network connected in parallel with N1 winding was mainly detected, and it felt that there was no abnormality. Take the oscillation board and replace all the oscillation chips and peripheral circuits. The fault remains after power on. Note: there are no problems in the, oscillation and voltage stabilizing links, and there are no abnormalities in the load circuit after rechecking. The maintenance is in trouble.
Think of whether the switch transformer is broken? We have to rule out this possibility first.
Connect dc18v directly to pins 7 and 5 of 3844, and connect dc100v at the dc530v power input of switching power supply. After power on, the circuit vibrates and works. After a while, Z101 in the circuit in figure (c) begins to smoke. Observe that this circuit is a composite voltage absorption circuit, and there are resistance capacitance absorption circuits connected in parallel at both ends of Z101. After temporarily removing Z101, measure the DC output voltage of each circuit, and its height is proportional to the input voltage (at this time, the quality of the switching transformer is self-evident).
So far, the truth of the fault reason has been revealed. Three 100V voltage stabilizing tubes are connected in series instead of Z101. Power on and test the machine, and the switching power supply returns to normalExample 21. High frequency transformers, like iron core transformers, emit noise because the iron core is not tight. But the frequency of the switching transformer is very high, so it makes a high-frequency "squeak".
2. In general, the squeaking sound from switching power supply has little effect. If the sound is loud (the magnetic core is very loose), it will cause heating. Compress the magnetic core and drop 502 instant dry glue.Example 3
During the commissioning of the transformer, there should be no problem with the switching circuit. If the transformer rings, it must be the problem of the transformer. The transformer will ring if the coil is not wound well, the proportion of the primary and secondary coils of the transformer is inappropriate, the insulation paint is unqualified, the quality of the magnetic core, the air gap of the magnetic core is inappropriate, etc. In fact, it is also simple to solve the problem. Mainly check the dip insulating paint, the air gap of the magnetic core and the proportion of the primary coil of the transformer. If you still can't solve this problem, please replace the magnetic core and try it. When the air gap of the magnetic core is the same, some permeability of the magnetic core is different, which will cause the magnetic core to adapt to different switching frequencies, which will naturally produce a sound.
Example 4Class I: if you have conditions, you can separate the power circuit from the load, find a good switching power supply and turn on the load. Check whether the whole circuit works normally at this time. If the whole circuit works normally at some time, some problems are caused by the switching power supply on the original machine; If the transformer of the new switching power supply also affects the squeaking, it indicates that it is a load problem and has nothing to do with the switching power supply on the original machine.Class II: when it is determined that the switching power supply causes the squeaking, focus on checking whether there is a short circuit in any place. I have also encountered the squeaking fault caused by short circuit many times during maintenance. If there is no short circuit, please refer to the information on the maintenance of switching power supply. There is much to say here. In short, we will consider replacing the switching transformer after.
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