Re: uBITX adjustable power supply?

Jerry Gaffke

Maximum available output current will fall drastically as the output to input voltage ratio rises.
You might get 4A out if the input voltage were about equal to the output voltage,
it falls off from there as you ask for higher output voltages.
Also, as that voltage ratio rises, the output current gets much choppier and noisier,
demanding more from the inductor and diode and output filter cap for acceptable results.

These things can work, but as you have found the spec's they give are "optimistic" at best.

Here's a tutorial on boost converters:

And a datasheet for the chip used:

Note that pin 2 of the chip is an ENABLE pin, could pull that low during receive.
Most of these modules don't give you an explicit connection on the board to shut it down,
but if you study the data sheet of the part used it is often possible.

Using two modules, one for each FET as you suggest, should work on the uBitx.
Though that means two spots to adjust output voltage, and twice the number of places it can fail.
A single large boost switcher might be better.

Jerry, KE7ER

On Fri, Jul 20, 2018 at 01:28 AM, Tom, wb6b wrote:
My apologies for the stream of consciousness nature of these last few posts. But, if it turns out one of the power converters can't handle the load, I realized the uBITX does not use a center tapped output transformer. I might try supplying each half of the push-pull finals with a separate boost converter.

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