![]() To make test and evaluation easy, I used a single dual op amp and only one 12V supply. R4 is adjusted so that it drops about 2V at maximum signal level –this is very non-critical.Ĭ1 is a compensation capacitor –for faster performance, this may be adjusted down –if too low, the circuit may oscillate. Potentiometer R4 accommodates gross variations in the CTR (both devices). ![]() The easiest way to test performance is to connect a DVM between input and output. Adjusting R2 so that R1 + R2 ✴.7K causes the output of U2 to come close to the input voltage signal –further adjustment of R2 will trim for the difference in CTR so that the output voltage will exactly match the input voltage. At the same time the output of U3A presents a positive going signal to U2. When both op amp inputs are equal, the output of U1 stops integrating. U3-B turns on and provides a positive going feedback signal. At any rate, the LM358 is very inexpensive.Ī positive signal input causes the output of U1 to shift positive. There is the LM321 single op amp, but it is unpopular and comes only in the SO-23-5 SMD package. I do this because there is no DIP single device that will do the job (that I know of). I generally use the LM358 dual op amp whenever I need a single ground sensing op amp. To maintain a high voltage rating, use two single devices and match the CTR to some degree. While DIP optical couplers have up to about 5kV isolation capability, this circuit cannot support above about 100V or so because one of the outputs is fed back to the input amplifier –this puts the voltage isolation between adjacent pins on the device rather than across the device.
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