First results for "variable output voltage"

A project log for Low-Cost Programmable Power Supply

Chinese "LM2596 DC/DC buck converter with voltmeter" + "some wires" + "Forth" = "programmable power supply"

ThomasThomas 02/08/2017 at 21:563 Comments

The approach proposed by @K.C. Lee seems to be working: using the Forth snippet from the last log entry and a quick&dirty RC filter I can control the output voltage of the DC/DC converter even if the current filter output leaves a lot to wish for.

With an unregulated 12V power supply from the AR-box *), 0% PWM results in 14V output voltage. The output voltage drops to about 2V at 50% PWM. The RPM of a connected DC motor can be controlled in small increments by changing the PWM value (I know, for a motor a constant voltage supply and a PWM output would have been just as good - the motor was just a load for a test).

All in all it looks promising, but I first need to build a set-up for testing. For this I need a switchable load to do basic dynamic testing, a more reliable primary power supply, and good wiring.

*) thanks to @esot.ericor this "croponym"


esot.eric wrote 02/10/2017 at 03:14 point

Just a recap, you're using PWM tied to a switching-supply's "adjust" input to adjust the output-voltage of the switching-supply...? So, the PWM isn't driving the motor, the switching-power-supply's output-voltage is driving the motor...

Sounds loopy, but I guess that's the point of feedback-loops ;)

In a way it's a Class-D amplifier.

Haha, "croponym". I've gotta say, reading this made me do a
double-take seeing the phrase "AR-box" somewhere other than on one of them boxes.

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Thomas wrote 02/10/2017 at 04:03 point

Yes, iIt's a non-linear inverting Class-D amplifier :-) 

I'm a bit concerned about the curbed control gain when the offset to the LM2596 feedback loop gets higher than about 500mV (i.e. when the DC/DC output voltage is low). I guess that the approach is still sufficient for a kludgy MPPT because there the required voltage variation ratio (high/low) won't exceed 2:1.

With croponym we have a new word. Check Google!

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esot.eric wrote 02/11/2017 at 07:23 point

I'll have to take your word on the MPPT and curbed-control-gain stuff ;)

"croponyms" aren't so unusual in this era, congrats on coining the term to describe 'em!

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