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Why does the switching power transformer make noise?

View: 48505/27/2019  

[Introduction] why does the switching power transformer have abnormal sound?

This needs to be considered from all aspects, such as the transformer process, loop, core, switching power supply load, etc.




Why does the switch power transformer have abnormal sound?

This needs to be considered from all aspects, such as the transformer process, loop, core, switching power supply load, etc.




The cause of abnormal sound of switching power transformer


(1) Process problems of transformers


1. Paint drying F is not in place, resulting in the combustion core is not strong cause mechanical vibration and announced market:


(2) The length of the air gap is not suitable, resulting in the variable jaw T.


The line package is not wrapped tight may also lead to noise;


(4) The magnetic core combination has air gap, high frequency caused by air vibration and announced sound (transformer if through the vacuum, a - like will not sound)




(2) Circuit problem of transformer


The problem of transformer loop refers to the transformer loop vibration and then causes the transformer to bark.




(1) Circuit board wiring is improper, and then form a disturbance caused by vibration, resulting in noise:


(2) Feedback loop parameters are not set properly, resulting in the loop is not stable vibration and announced sound:


(3) The quality of the loop element equipment, such as the lack of input filter capacitance capacity, the flow rectifier fast recovery diode quality is not good, power MOS tube quality is not good, RCD recoils absorption loop high voltage capacitance or diode quality is not good, and so on, these problems may lead to vibration and cause noise.




(3) Core problem of transformer


When the transformer core is saturated, the current in the coil increases, the transformer heats up and suffers from self-excited vibration. The vibration of the coil causes the surrounding air to vibrate and then announces the noise.




(4) Load problem of switching power supply




(1) Switch power supply in the case of no load or light load, in some of the T.




The reason for this phenomenon is that when there is no load/light load, the instantaneous registration time of the switch is too large, and then the energy of the transmission mountain is too large, and then the voltage is too strong, and the demand for a long time to restore to the normal voltage, so the switch needs to stop this operation - period of time, so that the switch is T.

Make a form that causes the mutator to attack at a lower frequency (regular quietness full cut u!

;

A vibration of a period or frequency with a dramatic change in duty cycle.




(2) transformer T. For the severe overload state, there is always burning ding can be one by one this is the source of many power incineration before the "scream".




Why does the switching power transformer make noise?




Abnormal noise of switching power transformer and its solution example


Example 1:


After the power on the switching power supply appears burp sound, test each output dc voltage is very low, and is not stable.

First from the load circuit check, no damaged components.

Later, the voltage absorption network connected in parallel with N1 winding was detected, and no abnormality was found.

Take the vibration plate, the vibration chip and peripheral circuit are replaced, on the fault still.

There is no problem in clarifying, vibration and voltage stabilizing.

Maintenance is in trouble.




Think about whether the switch transformer is broken?

You have to rule out this possibility first.




Connect DC18V directly to the 7 and 5 feet of 3844, and connect DC100V to the input end of DC530V power supply of the switching power supply. After power on, the circuit will start to vibrate, and at a moment, the Z101 in the circuit of figure (c) starts to smoke.

Observe that this circuit is a compound voltage absorption circuit, and Z101 has a resistance and capacitance absorption circuit in parallel at both ends. After temporarily removing Z101, measure the dc output voltage of each circuit, and its bump and input voltage are all equal (the quality of the switching transformer is self-evident at this moment).




At this point, the cause of the problem has become clear. Replace Z101 with three 100V regulator tubes in series. Power on test machine, switch power supply operation returns to normal




Example 2:


1. The high-frequency transformer is the same as the core transformer, and the declared noise is caused by the loose core.

But the frequency of the switching transformer is high, so the high frequency "squeak" is declared.




2. In general, the squeaking sound of switching power supply declaration has little influence.

If the sound is very loud (the core is loose), it will cause heat.

Press the core tightly and drip 502 instant dry adhesive.




Example 3:


When transformer debugging, switch circuit should do not have what problem, if present transformer to ring, that is the problem of transformer certainly, coil did not wrap a system, transformer primary and secondary coil share are inappropriate, dip insulate paint is unqualified, magnetic core quality problem, magnetic core air gap is inappropriate can form transformer to ring.

To solve in fact also brief, the first view dip insulation paint, magnetic core air gap and transformer primary coil share.

If still cannot solve this problem, ask you to replace core to try, below the case with identical air gap in core, core of magnet of some of permeability is not same, can form core to suit the dissimilarity of switch frequency, natural meeting sends sound.




Example 4:


Class a: if you have the condition, you can separate the power circuit from the load, and find a good switching power supply and connect the load.

See at the moment whether the whole circuit is normal operation, if some time when the whole circuit is completely normal operation, then some of the original switch power supply problems;

If at the moment will be the new switch power transformer also affect the squeaking, clarify is the problem of the load, and the original switch power supply.




Type two: when it is determined that the switch power caused by the squeaking, then the point to check whether there is any place where there is a short circuit of the situation, I in the repair, also encountered a lot of short circuit caused by the squeaking fault.

If do not have the circumstance of short circuit, ask you to consult the data of repair respect of switch power source.

There is much to be said here, after all, before considering replacing the switch transformer.


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