Current sense schematic question

Posted on Feb 6, 2014

Looking at different ways to do current sensing, using regular opamps, rather than dedicated chips like the MAX4073T/F/H, which work well, they are just rather expensive. So while poking around i found an article written by Bob Pease, , which talks about `error budgets` And the schematic fugure two, caught my eye As far i understood what Bob was talking about that curuit, should generate 2 volt on the output

Current sense schematic question
Click here to download the full size of the above Circuit.

if we have one amp through the shunt resistor, I decided to run the shcemati through an simulation tool or two to see whats up. In the one tool i tried where i had the PN4250 transistor, i consistently get around 6 volts on Vout, no matter what the current is. I tried in LTspcie, and that just gives me 11. 2 volts (see attached model, i dont know if the lm258 and the 3906 suitable for this) If you add a +14v (or more) supply just for the LM258 the circuit will operate correctly, otherwise you need an op-amp which functions with inputs close to its +ve supply which are not common. JensAndree, the hall sensor is 3$ in small quantiites, so its a bout twice the price of the max4073m but i guess that the hall sensor might be better over larger current ranges and with AC. looks very interesting, and i can see that you also found the mcp600x series opamp, i have found that that microchip has a lot of interesting analog parts. I am building a related system to yours, to power a server 24/7 using solar panel s and batteries, with a power brick as a backup. The current monitor pcb you saw in the post is 1oz copper and is easily handling +/- 15A. I would like to test the board at the maximum ATO fuse rating of 40A when I get the time. I think I will have to up the pcb copper to at least 2oz for that much current. Good luck with your project. I do all of the lighting in my house with LED lights I designed and all 24 lights are 100%...

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