50Hz Hum Noise in power supply

[shravanraghu]

Hello
I wanted to know how I could remove the 50Hz noise by hardware? The problem is the adapter comes without a GND pin and it gives an output of DC12V--4A. The 50Hz signal interferes with the measurement.
RC low pass filter is one of the solutions but due to high current, it dissipates a lot of heat.
LC low pass filter is another solution but I am not getting the components for the ratings that i need.
Does anyone know any other solution?
Thanks
Shravan Raghu

 

[andre_luis]

In fact, some values found on calculus are quite unreal, but need to take several iterations, assigning new values to some components in orther to get more aproppriate values for others, and even at this point, you might perform some series/paralel combinations to fit desired value.

Anyway you are not employing the correct filter; In order to remove noise becoming from mains you must select the Noch filter.

 

[shravanraghu]

ya i do know that notch filter is the correct one but it requires a load/resistor which dissipates heat. So thought of implementing a low pass filter.

 

[Audioguru]

The 50Hz is probably a sawtooth waveform that has many harmonics of 50Hz which will be missed by using a notch filter.
Have you tried increasing the value of the main filter capacitor or replacing it?

 

[andre_luis]

ya i do know that notch filter is the correct one but it requires a load/resistor which dissipates heat. So thought of implementing a low pass filter.

It makes no sense; Every filter acts as a "black box" system, having all components calculated to a normalized load placed on output, so that the loss due to dissipation at inner devices could occur at any one other kind of filter.

 

[Borber]

What if your adapter is switching mode and has low enough 50Hz ripple on output and problem is bad ground on your measuring instruments so called ground loop problem?

 

[shravanraghu]

I haven't implemented the filter and the adapter has no GND pin. I wanted to know if there is any other solution apart from filters?

 

[Borber]

None of cheap adapters has ground pin. Isolation between mains and output is sufficient safety method.

 

[Audioguru]

Is the hum electrical noise at the output of your adapter or is it mechanical noise in your adapter?
How did you measure its frequency? Is the hum present without a load or only with a load? What is the current rating of the adapter and how much current is your load? What is the amplitude of the hum when it has your load?

Usually an adapter uses full-wave rectification to reduce the size and cost of its filter capacitor because then its hum is 100Hz instead of 50Hz. If the hum frequency is actually 100Hz then maybe a diode or two in your full-wave rectifier has failed or has a bad solder joint? Did it get too hot and has unsoldered itself?

 

[FvM]

The discussion course shows that the problem hasn't been properly analyzed.

A unsuffciently filtered power supply with full wave rectifier shows 100 Hz rather than 50 Hz hum.

50 Hz common mode interferences together with high frequent switching noise can be expected from an isolated SMPS. The most simple way to get rid of it would be a secondary ground connection.