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Filter for 220VAC 50Hz

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strahd_von_zarovich

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Hi everybody,

I am looking for filter for my power supply input. Power supply is a 220VAC 50Hz to 24VDC converter. However, a very powerful noise nearly at 10kHz is coming from AC and this noise leaks into my analog circuits. Every circuit has its own low noise regulators, but still i can't get rid of 10kHz and it's harmonics. :-( . Probably it is coming from AC ground bacause when I plugged out , 10kHz and its harmonics are gone. However, when it is plugged in and power switch is off, they are still coming. How can i filter this noise, which components can i use for this purpose what are their names.

Thanks in advance.
 

Hi,

what comes into my mind: Use a common mode choke.

But it´s difficult without seeing any circuit diagrams, PCB layout and values.

Maybe you don´t use a proper GND plane. Maybe you use long traces acting as "antennas"

Klaus
 

Either LC or RC low pass filters can be used for this purpose. Where the LC filter is more efficient than RC filter.
But for basic power supply circuits, LC filters are less popular than RC filters, as the inductors needed for the filter to work efficiently at 50 to 120Hz need to be large and expensive laminated or toroidal core types. However modern designs using switch mode supplies, where any AC ripple is at much higher frequencies, much smaller ferrite core inductors can be used.

To increase the smoothing action using the filter circuit, just one L-C circuit will not be enough. Several L-section filters will be arranged to obtain a smooth filtered output. Once the signal passes through the choke, if there is any fluctuation remains, it will be fully bypassed before it reaches the load by the shunt capacitor because the value of the reactance(XC) of the capacitor is very low compared with the load resistance (RL). The number of ripples can be reduced to a great amount by making the value of the reactance of the choke (XL) greater than Xc at ripple frequency.

To provide precise information about the types and values of the filters, it will be better if you mention few details
1. The type of circuit which you are using for this AC to DC conversion.
2. What is the actual source voltage for this circuit.
 

10khz noise….hummm……that to me sounds like either the ringing of an LC input filter, or from a smps which is operating (rightly or wrongly) in burst mode….and the bursting is at 10khz.
If its an smps What controller do you use?
Of course it could also be due to an unstable feedback loop, but please advise what is the controller, mode of operation (compensated feedback, hysteretic etc)

One things for sure...10khz isnt going to irradiate anywhere......why is it a problem to you......EN regulations dont usually even worry about conducted frequncies until they get up above 150khz.....apart from mains harmonics, but mains harmonics are much less than 10khz.....

...so why is the 10khz a problem to you?......i mean, do you have 10khz of huge ripple on your 24v output voltage?
 

Thanks for the answers,

KlausST said:
Hi,

what comes into my mind: Use a common mode choke.

But it´s difficult without seeing any circuit diagrams, PCB layout and values.

Maybe you don´t use a proper GND plane. Maybe you use long traces acting as "antennas"

Klaus
Click to expand...

Actually, it is a complete system and there are 8 different PCB designs in a metal box. However, the main problem is, I see this 10kHz and it's harmonics while the system is not working. I tested this by touching a RF cable which is terminated by 50 Ohm, to the box. I only touch with outside of the connector ofcourse which is ground. But these noises can easily leak to the audio analyzer. Also, while my system is working i can see these noises with my ADC.

hobbyckts said:
Either LC or RC low pass filters can be used for this purpose. Where the LC filter is more efficient than RC filter.
But for basic power supply circuits, LC filters are less popular than RC filters, as the inductors needed for the filter to work efficiently at 50 to 120Hz need to be large and expensive laminated or toroidal core types. However modern designs using switch mode supplies, where any AC ripple is at much higher frequencies, much smaller ferrite core inductors can be used.

To increase the smoothing action using the filter circuit, just one L-C circuit will not be enough. Several L-section filters will be arranged to obtain a smooth filtered output. Once the signal passes through the choke, if there is any fluctuation remains, it will be fully bypassed before it reaches the load by the shunt capacitor because the value of the reactance(XC) of the capacitor is very low compared with the load resistance (RL). The number of ripples can be reduced to a great amount by making the value of the reactance of the choke (XL) greater than Xc at ripple frequency.

To provide precise information about the types and values of the filters, it will be better if you mention few details
1. The type of circuit which you are using for this AC to DC conversion.
2. What is the actual source voltage for this circuit.
Click to expand...

I use this AC-DC converter for my system : https://www.mouser.com/ds/2/260/RSP-200-SPEC-806453.pdf
Actual source voltage for this power module is 230Vac 50Hz .

treez said:
10khz noise….hummm……that to me sounds like either the ringing of an LC input filter, or from a smps which is operating (rightly or wrongly) in burst mode….and the bursting is at 10khz.
If its an smps What controller do you use?
Of course it could also be due to an unstable feedback loop, but please advise what is the controller, mode of operation (compensated feedback, hysteretic etc)

One things for sure...10khz isnt going to irradiate anywhere......why is it a problem to you......EN regulations dont usually even worry about conducted frequncies until they get up above 150khz.....apart from mains harmonics, but mains harmonics are much less than 10khz.....

...so why is the 10khz a problem to you?......i mean, do you have 10khz of huge ripple on your 24v output voltage?
Click to expand...

Well, 10kHz leaks into the my analog circuits, and effects my system performance. I haven't tested my 24V output voltage.However, even if it has huge ripple, it must be filtered in my analog circuits, because I use very low noise linear regulators.
 

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