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Messages - rockets4kids

2
Project logs / Re: Power Bar - A small breadboard power supply
Although transistors are just fine for the role of controlling voltage, you need to realize they are current devices, not voltage devices.  As such, in order to regulate voltage as current changes, you are going to need to adjust the input voltage.  This is why you see your PWM-generated voltage change with load.

The problem with this is two-fold.  First, the capacitance in your PWM voltage source is going to limit response time.  While you might not see any problems at low frequencies with low loads, switching higher loads at higher frequencies is going to result in a lot of noise on your output.  Even if you can get the response time if your PWM voltage source down to zero, you still have the time delay in the control loop on your MCU.

When you let an op-amp control the regulation, you don't need to worry about the response time of your PWM filter or control loop as you are just generating a fixed, constant reference voltage.

But again, this is coming from someone who isn't really an analog guy, and I'm speaking entirely from theory and little practice here.  Hopefully someone with stronger analog skills can jump in and school the both of us.
3
Project logs / Re: Power Bar - A small breadboard power supply
My analog skills are poor, but it appears as if you are doing full regulation in software.  If this is the case, how well does this work under varying loads?

While it seems reasonable to generate a reference voltage via PWM w/ feedback, it seems as if you would do better to use this to drive an op-amp to perform the actual regulation.

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