Programmable power supply

Question

I have been assigned to design a kind of programmable power supply. Can't decide on a way to make it. Need help with this.

This is a high level block diagram of the required system:

How it works (How it should work)

The system will be given 0 to 10 Volt variable input, which decide output voltage. The output should be proportional to the input. So that when input is Min, output is also Min (i.e. 0v), when input goes to Max, output also should be Max (i.e.24V). Simply, if the input voltage is V_I, then the output voltage should be (24/10)*V_I

The output is drawn from the systems power supply, not from the input voltage. (Actually input and output should be isolated.)

I hope that part is clear.

Then there is another input (input 2). Let’s think about it as a Potentiometer. So that its value can vary between two values, for the sake of explanation, lets say it changes between -10 and +10.

Its role is like this. (I’ve mentioned it as tolerance.)

Output value is decided from the input 1. That value is changed a bit around the original value by this input 2. For example, if output is 10V now, I can increase it a bit by rotating my preset clockwise. Or decrease it a bit by rotating it counterclockwise. Maximum change, lets say, will be 10% of the set value.

That’s it. I tried to explain the thing to the best I can. If any clarifications are needed please ask.

This is the requirement. I’m very good at microcontrollers, But not much experienced in electrical side. I thought a lot to make this using microcontroller. May be there is, but can’t figure out.

But it doesn’t need to be microcontroller-based, this is an actual requirement. So if there is any way to achieve this, then I’ll move to that.

Please share your knowledge. If anyone can point me in an exact direction that will be much appreciated.

Answer 1

What you want is called a power supply amplifier or PSA in the business. You are essentially looking for a power amplifier with a gain of 2.4, although it only needs to drive in one direction but has to be isolated.

Think of how a power supply works. At some point there is a feedback signal indicating how high or low the output is and a reference that indicates what that feedback signal should be. The controller looks at the difference and tweaks the output up or down. You can control the output by changing the reference signal.

Isolation makes things more difficult. Sometimes this comparison to the reference is performed on the isolated side with a simple digital high/low indication transmitted back thru a opto to the hot side. The system still works as I described, but the reference is on the isolated side which is not where you want it.

This leaves two possibilities. Communicating the reference to the isolated side and doing the comparison there, or communicating the actual output level to the hot side and comparing it to the reference there. Both schemes have some merit, but I'd probably pick the first in a DIY project.

The best solution is to simply buy a PSA if you can find one with the right characteristics.