[GreenKeys] Building my own power supply

[John, W9DDD]

Hammond 169C isolation transformer.  Secondary taps for 90 to 130 volts. 
(90, 100, 110, 115, 120, 190)

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You said "tomorrow" yesterday.

The above comments or recommendations are SWAG. Use at your own risk.
John, W9DDD

On 8/13/2023 8:31 AM, Ethan Blanton via GreenKeys wrote:
> Windows XD wrote:
>> I'm trying to build my own power supply for my Teletype model 19, it needs
>> 120-130VDC of power @ 830Ma. I'm working on a circuit for it, but I don't
>> exactly know what I am doing because I've never done this before. Would you
>> let me know if I am on the right track to building a switching power
>> supply?
> This looks like a linear supply to me, but you cannot rectify the
> incoming AC to DC _before_ passing it through a transformer, you'll
> just burn up your transformer that way, with no voltage coming out the
> output except the instant when you plug it in and the instant when the
> primary burns through.  ;-)
>
> A linear supply is very reasonable for this, but you'll need a
> step-down transformer to something like 85-90 VAC.  You then put your
> bridge rectifier and filter capacitor on the _output_ of the
> transformer instead of the input, and voila -- you're done.  This is
> exactly what I use for my iron horse perforator.
>
>> P.S. I know it needs a snubber circuit somewhere and none of the actual
>> switching circuitry is there, I don't know enough to know what goes where.
>> [image: circuit.png]
> In theory you do, but in practice it probably doesn't matter.  The
> snubber prevents a high reverse voltage from kicking back out of the
> punch solenoid coil when the supply is cut, but since there are no
> other devices on the loop (and in particular no semiconductors that
> cannot tolerate the reverse voltage), I doubt you'll find you need it.
> If you did, you'd just put a diode antiparallel to the filter
> capacitor.
>
> Ethan
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