- #1
J_Sieg
- 2
- 0
Hi,
I'm looking to create a simple circuit to convert current on a nominal 120VAC line into a voltage. I have a few designs but am having some difficulty keeping parts count low and maintaining accuracy.
What I have is as follows:
- I am using a shunt resistor, outputting 1mV per ampere of current (0-15mV total).
- I take the output from the shunt resistor (120VAC +/- 15mV) and use it as an input for two op-amps (running single supply [+3V] differential amplification).
- From the op-amps, I take the output and make it positive only via some diodes, then through a filtering capacitor.
- This gives me a voltage proportional to the current, or should..
The problems I am having have to deal with two things...
First is parts count. That is a hugely inefficient way to do things, having two entire amplification circuits, even with a dual op amp. I am wondering if there is a way to do this with a single amp.
Second, pin voltage is exceeded, as even though the voltage differential is 15mV max, it is on a 120V offset.
Do any of you have ideas on how to simplify this circuit? Op amps that might handle 120V on a pin, preferably at a low cost? That also take monopolar power? I tried a voltage divider, but if I divide the offset, I also divide the signal and lower my read resolution.
Thanks!
I'm looking to create a simple circuit to convert current on a nominal 120VAC line into a voltage. I have a few designs but am having some difficulty keeping parts count low and maintaining accuracy.
What I have is as follows:
- I am using a shunt resistor, outputting 1mV per ampere of current (0-15mV total).
- I take the output from the shunt resistor (120VAC +/- 15mV) and use it as an input for two op-amps (running single supply [+3V] differential amplification).
- From the op-amps, I take the output and make it positive only via some diodes, then through a filtering capacitor.
- This gives me a voltage proportional to the current, or should..
The problems I am having have to deal with two things...
First is parts count. That is a hugely inefficient way to do things, having two entire amplification circuits, even with a dual op amp. I am wondering if there is a way to do this with a single amp.
Second, pin voltage is exceeded, as even though the voltage differential is 15mV max, it is on a 120V offset.
Do any of you have ideas on how to simplify this circuit? Op amps that might handle 120V on a pin, preferably at a low cost? That also take monopolar power? I tried a voltage divider, but if I divide the offset, I also divide the signal and lower my read resolution.
Thanks!