[Milsurplus] Design for a cheap 400Hz power supply

[Dongen, Nico van]

I once owned an 180L3 and made a very simple and cheap power supply for =
it that is usable for a lot of other applications as well.

The biggest problem with most designs I've seen is that they all require =
a purpose build power transformer with a specific number of windings on =
the primary and secondary side making it difficult to build. This is how =
I did it.

I use a clock IC that outputs a square wave adjustable between 30 and =
3000 Hz. They feed a pair of Darlington transistors connected to the =
secondary of a 220V / 2x 24V transformer.=20
In the DC input to the Darlington I put a 3-pole voltage regulator so I =
can adjust for the required voltage output. With about 12 volt input I =
get 115V output  =20
Most aircraft gear is working on 115V 3 phases so I connected a =
capacitor on one of the output lines to create the third phase. It =
produces a very rude waveform but the 180L3 was working nevertheless and =
it only takes a handful of components.=20

I know all the theory of running transformers in saturation and output =
spikes on using square wave input but it works and doesn't't run hot. =
The 180L3 115V requires low  power 115V for the control logic only so a =
normal transformer will do.

Based on this I also made a battery replacement unit by putting a =
rectifier circuit behind it. Then you have to watch out for spikes and =
put some filtering in front of your circuit.=20

I've build a version a little bigger that produced 100W on 115V as well =
and I used a transformer in torroid shape for that because torroid's =
handle square waves better.

With a bit of luck all required components could be found in your =
junkbox. If interested, I can provide the schematics.

Regards,

Nico   PA3ESA
Netherlands