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Building a multiple mode power supply...

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Externet

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Which way to put together a power supply that will work from a standalone 12V lead acid battery source, not being charged (not 14V)
With two selectable outputs (not simoultaneous):
1- > Adjustable pure DC from about 30 VDC to 160VDC, capable of 3 Amperes.
2- > Pulsed DC 30 to 160 V, up to 3 Amperes, from 1% to 50% duty cycle square wave.
[- An optional but not needed yet, additional future mode could be 0 to 120 VAC adjustable output, up to 3 Amperes, 20 Hz to 120 Hz.]

Seems a plain off-the-shelf ~500 Watt inverter for recreational campers and alike should be able to provide the first stage from 12VDC to 120VAC which rectified and filtered can become 160VDC. But I have tested a couple that refuse to work unless there is at least 13.5V on the battery (being charged)
Then a method to make it variable/adjustable.
From the pure DC source, adjustable chopping by PWM for the second mode ?

Battery-----> inverter -----> rectifier------> filtering -----> linear regulator----->output mode 1-----> chopper-----> output mode 2 ??

What building blocks or circuits do you see as convenient to use? Or, modifying an UPS ? Modifying a subwoofer mobile amplifier ? Modifying a 500W inverter ? Other ?

It is for an experimental soil tester.
 
Thanks.
Its specifications show 250V 3A 300 W output. They are not showing a good start. 250 x 3 is not 300.

Doubtful specifications at >$800, plus an inverter to make it work from 12VDC, plus still need to fabricate the high voltage PWM chopper, sort of not convincing.
 
If you go the UPS route, better not use a 500W one, the losses in your added regulation alone will likely preclude it, plus you'll be wanting a little headroom to play with, these things are rarely capable of repeating the quoted ratings for anything in the real world, maybe hitting the quoted spec 2 in 5 times when in good condition. I wouldn't try to make the inverter variable either, I would keep it pretty much stock, with maybe a modification of the battery switchover circuits to allow for a lower terminal voltage or something and just use it as your main power plant. After all that's it's intended purpose and probably where it will be most efficient. Adding your other functionality to it will also result in easier troubleshooting :)
 
Thanks.
OK; a suitable ~600W inverter and rectifier + filter will put me on the 160VDC range.
Now, to adjust that DC down to 30V on a linear pass transistor, I do not care about waste and the size of the heat sink.
Found only one adjustable voltage regulator that accepts up to 450V; if could drive the pass transistor. Components could be Supertex LR8 and have several 2SC2625 (400V 10A).

For the chopper, have on hand a bunch of 2SK2648. (800V 9A)

Does it look doable ?
 
Thanks.
OK; a suitable ~600W inverter and rectifier + filter will put me on the 160VDC range.
Now, to adjust that DC down to 30V on a linear pass transistor, I do not care about waste and the size of the heat sink.
Found only one adjustable voltage regulator that accepts up to 450V; if could drive the pass transistor. Components could be Supertex LR8 and have several 2SC2625 (400V 10A).

For the chopper, have on hand a bunch of 2SK2648. (800V 9A)

Does it look doable ?
 
I was thinking that if absolute variability is not needed, perhaps use a range switch with a load dump and smaller switching supply to get you close to your window of interest and then a smaller linear regulator to dial in your exact requirements. I think overall it's doable, but will require major cooling either way going the purely linear route :D
Now that I have thought about it a little more, the problem might be easier tackled using one primary supply (UPS etc) and one variable switching supply, the latter requiring to be designed from the ground up for the application. Perhaps one of the others here with SMPS design experience might be able to shed more light on the idea :)
 
You coudl put together a switcher with a sg3525 and a etd44 ferrite transformer to provide you the dc supply up to 160v, on the o/p of that a pulse gen and a high voltage fet to generate your pulses.
Which does involve some smps design.
A quicker way would be to hack a 12v inverter, draw out the schem, theres a god chance it will be controlled by a standard smps chip, from that suss out how to disable the undervoltage lock out, mod the feedback to give you adjustable o/p voltage, finally remove the 50 or 60hz gen for the o/p transistors and replace it with a pulse gen circuit matching your description.
All this would take a reasonable amount of jigerry pokery and knowledge.
 
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