Isolating and Analoge Signal

Thread Starter

brunodrt

Joined Mar 29, 2014
13
Hello All,

I'm looking to find a solution to isolate an analogue signal. I've searched isolated op-amps but the ones I've found are more suited for current sensing ( up to 200 or 300mV ) and I needed something that could go up to( or near ) the supply voltage.
Does anyone knows about what could I use ? I was trying to avoid using and isolated ADC because i don't have any communication ports to use.

Thanks.

Best Regards,
BD
 

Gibson486

Joined Jul 20, 2012
336
you could use those AC opto couplers. Kind of a pain to design with, but they are nice when you get it going. I asked a similar question a few months ago...The issue is if you are current constrained. This would not be a good option.
 

Thread Starter

brunodrt

Joined Mar 29, 2014
13
Tell us exactly what are you trying to do (voltages, currents, signals, etc.) and why you think you need isolation.
The voltage can vary from 4.5V to 0.5V. The signal can be a DC voltage or a variable amplitude pwm.
The isolation is a requirement for the circuit.
 

crutschow

Joined Mar 14, 2008
27,198
variable amplitude pwm
PWM does not have a variable amplitude.
Do you mean the average value (duty-cycle) of the PWM signal is varying?

It's much easier to isolate a digital signal since it's simpler, and there is no concern about the accuracy of the isolation, but, it you truly need to isolate an analog signal, then the post #2 solution would seem to be a good way to go.
 
Last edited:

Thread Starter

brunodrt

Joined Mar 29, 2014
13
So is this a DC waveform (pwm), or an AC one? The above makes me think it's in the DC domain.
its a complex signal that represents different states . 5V DC represents one state, a pwm from 0 to 4 V a different state and from 0 to 2.5V another state ( its an example )
 

Ian0

Joined Aug 7, 2020
2,196
It would be much easier to isolate if it were two or three simple signals, rather than one complex signal.
e.g. one logic level signal, and one variable width PWM signal
 

michael8

Joined Jan 11, 2015
137
I'm looking to find a solution to isolate an analogue signal. I've searched isolated op-amps but the ones I've found are more suited for current sensing ( up to 200 or 300mV ) and I needed something that could go up to( or near ) the supply voltage.

Could you level shift it down to be locally ground referenced and then use one of the isolated op-amps?
 

crutschow

Joined Mar 14, 2008
27,198
ts a complex signal that represents different states . 5V DC represents one state, a pwm from 0 to 4 V a different state and from 0 to 2.5V another state ( its an example )
Sounds like all those signals are some form of digital signal (DC level or PWM).
Is that true?

Is there some significance to the PMW signals being different amplitudes?
 
Last edited:

Thread Starter

brunodrt

Joined Mar 29, 2014
13
I'm looking to find a solution to isolate an analogue signal. I've searched isolated op-amps but the ones I've found are more suited for current sensing ( up to 200 or 300mV ) and I needed something that could go up to( or near ) the supply voltage.

Could you level shift it down to be locally ground referenced and then use one of the isolated op-amps?
That could be an option depending on the resolution of the adc . Because at those levels of voltage any noise could be mistaken for a different stage
 

Thread Starter

brunodrt

Joined Mar 29, 2014
13
Sounds like all those signals are some form of digital signal (DC level or PWM).
Is that true?

Is there some significance to the PMW signals being different amplitudes?
Yes, each "stage" requires a different action from the controller. So if I have 5v is idle, but when the voltage drops to 4V its the first stage, when the PWM starts, its another stage and so on.
 

Ian0

Joined Aug 7, 2020
2,196
So, isolate two separate signals, one which is on if the input is 4V and off it is 5V; and then isolate the PWM. It just needs a comparator with the reference set to 4.5V and two opto-isolators, the second being quite a quick one such as the H11L1
 

BobaMosfet

Joined Jul 1, 2009
1,773
its a complex signal that represents different states . 5V DC represents one state, a pwm from 0 to 4 V a different state and from 0 to 2.5V another state ( its an example )
Okay-- DC domain. But is it analog? Analog means a smoothly transitioning signal over time, not sharply delineated 'steps'. Is the voltage changing in a stepped fashion, or smoothly?
 
Top