noise in TOP249Y
I am giving i/p( 300 to 450Vdc ) to a top249Y sw based power supply . O/P is 170V Dc with secondary side zenner feedback. I am getting very light audiable noise as the o/p load increses.
The audiable noise starts as soon as the controller enters in the continous mode from discontinous mode.The audiable noise amplitude and frequency varies with the variation in 6E8 resitance( 10E to 2E2 ) placed in series with the 47mfd el cap at ghe control pin.
Comments
Hi,
I would guess that it is your transformer that is making the noise. I would not modify the resistor in series with the 47 uF capacitor that is connected to the control pin since this affects your feedback loop.
I would guess that the noise is coming from the transformer. Try to see if you can hear exactly where it's coming from or if varnishing the transformer reduces the noise. If this does not work you can reduce the operating flux density of the design which should reduce or eliminate the audible noise.
Also we have an application note that is written about audible noise for TinySwitch but some of the information is also applicable to TOPSwitch. You can find that app note here: http://www.powerint.com/sites/default/files/product-docs/an24.pdf
I hope this helps!
Wesley,
I have varnished the transformers.
My operating flux density is 2000 Gauss.
Further why does the noise start when the system goes into continous mode i.e when the o/p load is typically > 70%.
I know that playing with 6E8 resistance is normally not recomended. But if the noise is coming from the transformer then how does the control loop parameters ( i.e changes in 6E8 resistances ) change the amplitude and frequency of the noise.
FFurther more the noise / audio frequency can only be seen across the clamp rresistor when the oscilloscope time base >> 1/66Khz.
If this is the case it may be that the type of capacitor you are using in the clamp circuit is actually the noise culprit! Is it a ceramic type capacitor? Try replacing the capacitor in the clamp with a plastic film type capacitor and see if the noise goes away. This is also described in http://www.powerint.com/sites/default/files/product-docs/an24.pdf
This may seem more likely given your low flux density and the fact that your transformer is varnished.
Let me know if that solves your problem. Thanks!
Welsey,
I know ceramic capacitors are culprit for audiable noise.
I am putting up this problem in this forum after trying out a lot of things.
I had put polyester capacitor ( 347 series from Vishay ) in the clamp circuit but was of no use.
Pawan.
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