[Milsurplus] DC-DC Buck/Boost Converter Regulation

[David Stinson]

>If your knocking down 28 volts to 12 for filaments
>why don't you just use a resistor?

Direct-heated series cathodes (811) in an oscillator circuit,
so filament regulation is very important to minimize drift.
Also - dropping 14 VDC at 4 amps is 56 Watts.
Big resistor, lots of heat in a situation where thermal drift
is already a problem.   These little dc-dc converters will
do the job without creating a lot of heat.



Not efficient but great for simplicity and if you're worried about voltage 
regulation you can always put a 14 volt Zener diode across the tube 
filament. Filament loads are constant and don't vary.

RF

-----Original Message-----
From: milsurplus-bounces at mailman.qth.net 
[mailto:milsurplus-bounces at mailman.qth.net] On Behalf Of David Stinson
Sent: Thursday, October 31, 2013 1:07 PM
To: nerd at verizon.net; milsurplus at mailman.qth.net
Subject: Re: [Milsurplus] DC-DC Buck/Boost Converter Regulation


----- Original Message -----
From: "Peter Gottlieb" <nerd at verizon.net>

> Boost converters frequently won't allow their outputs to go below
> their inputs.  You want a true buck-boost if you want to operate a 12
> volt load from 8-whatever voltage.  It's not completely clear the
> first one does that.

My interest is in using them as the regulating element in a primary filament 
power supply, bucking 28 volts down to 12 and which needs to be 
well-regulated, similarly to what one might do with an LM-317 but at higher 
currents.  Don't know how well they would handle a "noisy"
input.
Might need to "smooth" the input better before using such a device to 
regulate.
I'm not sure how much "swing" they can take on the input and still properly
regulate the output voltage.   I've looked at the datasheets and have
likely just missed the datapoint.  Hoping someone here has looked into it.
73 D.S.


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