Hi All,
This is my first time posting here, so please be kind
. I am designing a bench PSU using a STM32 micro (I know, overpowered, but I have a few on hand) that will produce a variable output from 0-24VDC, with current limiting up to 10A. The reason for this project is that my current bench PSU was one my dad built about 30 years ago from recycled components (parts were expensive back then) and is not capable of producing > 1A, and is quite hard to set exacting voltages on it.
Also, I should note that I am more of a software guy and enjoy programming the micro more then circuit design, and as such my circuit skills are rather limited.
So far I have built a voltage divider that is capable of being calibrated via a trimpot and is fed into the ADC of the micro, with a 3.6v zener diode to protect the input. I have also scrapped an old Chinese multimeter for it's current shunt, which through testing seems to produce 1mV for every 30mA.
The problem is that this voltage is too low and I need to increase it's dynamic range back to 0-3.3VDC. I have played with various op amps (first time user of them) to perform this which works nicely except for they all need around 10mV or more DC offset before they begin to operate. I tried providing the op amp with a +/- 5V supply which also overcame this, except I have no idea how to offset the negative voltages back into the positive range for the MCU.
All I need is a simple circuit that performs a voltage amplification of the voltage difference across the shunt that can either be fed into the MCU directly or is high enough for an op amp to perform the final amplification.
Note: I do realise there are op amps that have input offset voltages of < 1mA, but I live in an area that procuring parts is rather hard. On hand I currently have most standard transistors and a few basic op amps, including those that will operate on a single supply voltage.
Any help on the matter would be greatly appreciated.