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RE: Cheap DC Filament PS

Posted by Triode_Kingdom (A) on June 6, 2017 at 10:25:57

In Reply to: RE: Cheap DC Filament PS posted by coffee-phil on June 5, 2017 at 14:28:35:

Yes, if only one voltage is required, the combination of a switcher and LDO regulator (with current limiting) is probably the smallest package and least heat. It's also very inexpensive. The need for 6.3V and 12.6V on the same chassis changes all that. In my case, I want to be able to use 6V and 12V output and driver tubes. I also want to be able to switch between 6V and 12V versions of the same output tube. Current draw with a quad of 6V outputs will be double that of 12V tubes, so a linear regulator doesn't seem optimal for this use.

I only see a couple options here. One would be to use a separate, small switching supply for each voltage. That would require a delay circuit to be sure the supplies start reliably when the tubes are cold. I'd like to avoid that additional complication if possible.

The second option would be a power supply with at least 18 VDC output driving a DC-DC buck converter. The buck converter could reduce the voltage to either 12.6V or 6.3V, selectable by simply switching a resistor. If a linear supply is used, nothing else would be required. Use of a switcher might require a LM338 wired as a current limiter between the supply and the buck converter. The downside here is that 12.6V and 6.3V wouldn't be available simultaneously, and some of my upcoming designs will need that.

As it now stands, I'm leaning toward the use of a single supply and two buck converters to get this done. The converters are very inexpensive,
only a few dollars each, and also very small if 3A or less is needed. Either a linear supply or a small 24V/2A switcher could be used. The switcher might still require a current limiter, but it's also possible the self-limiting of the buck converters will be sufficient.

Looks like I have more experimenting to do...

Edits: 06/06/17

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