non common ground buffer

[gehan_s]

hey all,

i want to buffer a voltage between 2 DC circuits with different grounds. a traditional op amp buffer won't work as i am not prepared to connect the 2 grounds together. what i would want is something like an optocoupler but with linear characteristics. can anyone suggest a method for doing this ????? (the voltage that i want to buffer is in the range of 0V to 5V. the buffered voltage will actually be an analog input to a PIC).

thanks in advance !!!!!!!!!!!

 

[carp3]

you can measure voltage on the other side and send it as digital signal to your PIC in your side.

also you can use Analog Optocouplers

 

[Tunelabguy]

OK, the two DC circuits may have different grounds, but is there any limit to the voltage difference between these two grounds? Or are they totally floating from each other so that no reasonable limit can be guaranteed? If there is a limit (like only 7 volts or so) then you can use a differential input op amp on the PIC side. Make sure the power supply rails of the op amp are wide enough (maybe +/- 15v) to cover the 5-volt signal plus whatever difference in grounds there may be. If you are willing to suffer some loss of gain you can even design the op amp circuitry so that the differential inputs exceed the common mode limits imposed by the power supply rails, but due to the input resistors the voltages at the op amp terminals is within the power supply rails. But if the two grounds are really floating with respect to each other then this whole discussion is moot as you cannot use it. Just thought I would throw it out there just in case it might apply.

 

[goldsmith]

hey all,

i want to buffer a voltage between 2 DC circuits with different grounds. a traditional op amp buffer won't work as i am not prepared to connect the 2 grounds together. what i would want is something like an optocoupler but with linear characteristics. can anyone suggest a method for doing this ????? (the voltage that i want to buffer is in the range of 0V to 5V. the buffered voltage will actually be an analog input to a PIC).

thanks in advance !!!!!!!!!!!

Hi Gehan
one of the simplest ways is using a linear opto coupler e.g IL300 !
Best Wishes
Goldsmith