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Electronics => Beginners => Topic started by: Fowflux on February 18, 2016, 06:42:37 pm

Title: Power supply controlled by microcontroller and powered by USB
Post by: Fowflux on February 18, 2016, 06:42:37 pm

For a project I want to build a simple dual power supply that can be controlled through a microcontroller.
It should be powered by USB (so 5V), but should be able to provide voltages in the -20V through 20V range. To be more exact I want two outputs: one that ranges from 0V to around 20V, and another one that ranges from -20V to 0V. As said before, the output should be controlled digitally. It doesn't have to deliver much current (like 100mA max).

I have no real experience with powering electronics so I came here for some help. I had a few ideas to tackle this problem and would like to get some feedback if these ideas would work, or if there are some better ways to solve this problem :).

The first problem is to be able to create around +20V and -20V from the 5V provided by the USB.
My first thought was to use a linear regulator (or maybe a DC-DC converter?) to boost the 5V to +20V which shouldn't be that hard I think. However a problem arises when I want to create the -20V from the supplied 5V, does anyone have a suggestion how I could do this?

The second problem is how to make the output controllable from 0V to +/-20V. To solve this I have two possible solutions: using a (non)inverting amplifier circuit, where the opamps are powered by the +/-20V that were created by the previous paragraph, and the input is provided by the microcontroller (through PWM and a low pass filter to create an analog signal). So by adjusting the PWM DUT I can control the output of the non-inverting (supplied by +20V) and the inverting (supplied by -20V) circuit.
Another possible option I found would be using a digitally controlled potentiometer to adjust the voltage in some sort of circuit, but these are pretty inaccurate by my understanding?

So the main question is how to create the +/-20V and if my proposed way of controlling is going to work.
Thanks in advance!

Gr, Fowflux

Title: Re: Power supply controlled by microcontroller and powered by USB
Post by: mstoer on February 18, 2016, 07:17:40 pm

I think you might be demanding a bit much of the USB port.   The standard is 500mA for USB 2.0 and  you want that to supply not only your outputs, but all your control electronics.