I am currently working on a high-power 28S lithium-ion charger for EV. I'm on a constant current stage, so you don't have to worry about all that balancing thing, I just want a constant flow of 15A through my 28S cells. I looked upon some circuits online that achieve a constant current with a control loop with an op-amp and a current negative feedback as can be seen in the following image:

standard constant current circuit

This is all fine and standard and I get how it works, basicly the opamp increases its output voltage until that is negative input current feedback is the same as its positive input.

However, I was looking for some other proper charger circuits and stumbled upon the an iMAX B6 like circuit, which is can be seen here: RC-Power_BC6_Charger

circuit in analysis

I am trying to analyse this circuit and my question briefly is: what those parts I marked are responsible for? I get R7 and C3 form a low-pass filter, as well as R17 and C14 and I think R14 adds a gain to the circuit. But I don't get what those marked parts are for. I though I was some sort of summing amplifier, but this got me nowhere.


The input to R22, labelled OC1A appears to set the output current level. At a guess, it's a 0-5 volt signal. The two 100k resistors drop this to 0 to 2.5 volts. This is important because

PA7 appears to be a digital signal which forces the current to zero by forcing the - input of DA1:2 above the 2.5 volt maximum of the + input, driving the output of DA1:2 low, thereby turning off the FET. In normal operation, PA7 is held low, and the diode is back-biased, so it has no effect. R37 is there as a safety feature. If PA7 is completely absent, such as might happen if the source of PA7 loses power or there is a cable break, R37 pulls up the anode of VD2 and forces the output current to zero.

| improve this answer | |

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.