Op Amp output ripple stabilizing

Thread Starter

kingMoshe

Joined Apr 27, 2020
6
Hello,
The attached is an op amp circuit that give output voltage between 0 to 2.5 according to Vin.
Because I have switching component in my system, I got ripple and noises in the output (Picture attached).
How can I reduce the ripple / stabilizing the output voltage ?

Thanks,
Moshe.
 

Attachments

Papabravo

Joined Feb 24, 2006
15,453
How is the noise coupling into your circuit?
Where are your bypass capacitors?
Analog scope or digital scope?
How long is the GND lead on your scope probe?
The output does not look periodic, how many traces are displayed on top of each other?
Is this your first analog circuit?
 

Thread Starter

kingMoshe

Joined Apr 27, 2020
6
How is the noise coupling into your circuit?
Where are your bypass capacitors?
Analog scope or digital scope?
How long is the GND lead on your scope probe?
The output does not look periodic, how many traces are displayed on top of each other?
Is this your first analog circuit?
1. I Don't know.
2. don't have bypass capacitor
3. digital scope
4. GND lead very short
5. Adding zoom out picture, you can see the periodic spikes same as the switching frequency.
6. no.

Thanks,
Moshe
 

Attachments

BobaMosfet

Joined Jul 1, 2009
1,502
Hello,
The attached is an op amp circuit that give output voltage between 0 to 2.5 according to Vin.
Because I have switching component in my system, I got ripple and noises in the output (Picture attached).
How can I reduce the ripple / stabilizing the output voltage ?

Thanks,
Moshe.
Noise always exists in circuits- including on the ground plane. You can isolate your op-amp away using opto-isolation methods or use filters.
 

Papabravo

Joined Feb 24, 2006
15,453
If this is not your first circuit, you better figure out PDQ how it is getting there, Try a linear supply with the same output.
How come you have no bypass capacitors on the V+ and V- supply lines to the op amp. The deity does not provide when you forget. First guess is noise is coupling in through the supply lines. Is this a breadboard or a PCB?
 

Thread Starter

kingMoshe

Joined Apr 27, 2020
6
If this is not your first circuit, you better figure out PDQ how it is getting there, Try a linear supply with the same output.
How come you have no bypass capacitors on the V+ and V- supply lines to the op amp. The deity does not provide when you forget. First guess is noise is coupling in through the supply lines. Is this a breadboard or a PCB?
thanks for your answer, this is a pcb
 

Papabravo

Joined Feb 24, 2006
15,453
Is the switching supply a commercial unit, a separate board, or is it laid out on the same board?
Does the power supply have any output filtering?
 

OBW0549

Joined Mar 2, 2015
3,566
Just for future reference: switchmode power supplies and sensitive analog circuits DO NOT play well together without exercising extreme care and planning.
 

Papabravo

Joined Feb 24, 2006
15,453
Just for future reference: switchode power supplies and sensitive analog circuits DO NOT play well together without exercising extreme care and planning.
I use a well made SMPS with my Elecraft K3 Transceiver and have had no problems with it. The receiver on this rig can pick up signals from stations that cannot hear me with 100 Watt output into a 3 element beam.
 

Thread Starter

kingMoshe

Joined Apr 27, 2020
6
Is the switching supply a commercial unit, a separate board, or is it laid out on the same board?
Does the power supply have any output filtering?
Im sorry if I didn't explain myself so good, I don't use switching power supply. in my system there is boost converter circuit, only if the boost is on, I got the ripple at the output.
 

Papabravo

Joined Feb 24, 2006
15,453
Im sorry if I didn't explain myself so good, I don't use switching power supply. in my system there is boost converter circuit, only if the boost is on, I got the ripple at the output.
You probably don't want to hear this but I would start planning on a very careful re-layout of your board by somebody who really really knows they are doing. I'm talking 3 oz. copper for separate power and ground planes along with output filtering and possibly boost converter redesign.

I never thought the op amp input came from the converter, but good to know.
 

vanderghast

Joined Jun 14, 2018
53
5. Adding zoom out picture, you can see the periodic spikes same as the switching frequency.


Thanks,
Moshe
You can try to pump MORE current from the switching power supply to see if the spikes are then reduced. It may happen that the complete circuit could then solve a large part of the problem when compared to having just the OpAmp in use.

If you ever find a solution to that problem, take a patent, THEN make your solution public and you are very rich person. Every switching power supply maker would gladly add your solution into their product.
 

danadak

Joined Mar 10, 2018
4,057
1) What is ripple frequecy approximately.

2) What is part number of OpAmp you are using.

3) What are the values of the G setting R's used on the OpAmp ?

OpAmps have a PSRR (Power Supply Rejection Ratio) spec for their power
pins. PSRR is also a f() of frequency, and declines with increasing frequency
noise on their power pins.

Use a parallel combination of a .1 uF Ceramic MLC or disk, and preferably a polymer
tantalum on each power pin. Chart shows caps with low ESR. Low ESR is good.

1588696411586.png

https://www.renesas.com/us/en/www/doc/application-note/an1681.pdf

https://www.analog.com/media/en/training-seminars/design-handbooks/Basic-Linear-Design/Chapter12.pdf



Regards, Dana.
 
Top