Power supply filtering

[seyyah]

I have a circuit that produces some waveforms. I made a supply for that circuit to feed it. But when a motor or a similar thing kicks in or out the supply and the waveforms are affected badly. I tried to realize the circuit with different kinds like switching, linear etc. I also tried to filter both the supply or the waveforms but i could not success so far and i always face similar problems. The effect of outer sources/loads is shown in the picture. How can i eliminate this problem?

 

[oddbudman]

Whats the impedance of the lines being affected?

Is this design on a circuit board? if so perhaps put up a pic of it.

The noise looks severe.

oddbudman

 

[TekUT]

Could you post a schematic of your circuit, especially the power supply section?

Bye
Powermos

 

[seyyah]

I cannot give a whole schematic because its on the paper for now. I realized it on a board not on a pcb for now because the circuit is not completed and i am only trying a small part of it. The current circuit consists 2 comparators, a digital IC (74hc type) and an analog switch IC. I tried to keep the wires short and each IC has its 100nF. Comparator also has 10uF or more connected to its supply pins because it does not work correctly otherwise. I also tried to add some hyteresis and some r-c type filtering whereever applicable. A varistor at the 24v input seems to help to prevent the noise some. The input is 220vac to 24vdc then 24vdc to 5vdc. When the noise producing event occurs, the 5V is also affected so the rest of the circuit, so the main problem is to keep the 5V line clean which i could not accomplish so far.

 

[mesutyeni]

for smps the EMI filters (special bobins ) uses on the line input prevent the high switching frequency go out. it may be help you prevent signals going your circuit.

 

[TekUT]

Let me know, the motor was powered from your power supply section or is totally external of your circuit?

If the motor is powered from a source that is external to the your power supply section I think this is a conduction type interference due to the heavy nature of the noise, in this situation you've to do a mains filtering.

Anyway between the 24 V output and the input of your local supply you can use a common mode choke like the models that I've attached.

Bye
Powermos

 

[seyyah]

The motor has nothing with my circuit, it's external. Only they are on the same ac line. Also i won't be able to reach ac mains. There is a power supply in between it and my circuit. I can only reach 24Vdc. So what i'll do can only be to my circuit.

 

[TekUT]

The motor has nothing with my circuit, it's external. Only they are on the same ac line. Also i won't be able to reach ac mains. There is a power supply in between it and my circuit. I can only reach 24Vdc. So what i'll do can only be to my circuit.

Well, as a first approach I'll try to use the common mode choke listed above.

Bye
Powermos