> HELP !!!!!
>
> I need some advice on a voltage converter/ regulator that I have been
> building.
>
> For some reason no one makes a commercially available regulator that
boosts
> 12v up to 28V so that one can operate a 28volt aircraft device on a 12v
> Europa system.
>
> >From time to time there have been published circuits on this forum for
such
> a device and I have eventually got around to attempting to build one. The
> circuit is constructed around a LM2577 step up voltage Integrated circuit.
> By changing the component values the output voltage can be changed. The
same
> circuit is published on P235 of the latest Maplin catalog.
>
> Anyway my problem is this. Having assembled the circuit I tested it on the
> workbench and it works fine giving 27.8 volts across a 50 ohm dummy load.
> The trouble is that as soon as it is placed in a metal case the voltage
> immediately drops down to 13V.
>
> Losing the case is not really an option as it will probably affect the
other
> instruments and anyway even the proximity of a flat metal sheet (eg a
radio
> case) has the same effect. We tried grounding the case but it didnt work.
>
> Anyone in the know have any suggestions.
I can't check the Maplin cat. from here and it's a long time since I played
with electronis, but I have seen a metal case have an effect on circuits
with switching regulators and HF transformers. The voltage changed when I
screwed the lid on and it was something to do with the lid being made of
steel and being too close the the ferite core of the HF transformer.
If you are using a HF transformer, is it close to the case and what is the
case made out of? I'm sure you've checked for anything shorting to the
case...
Cheers,
Mark.
________________________________
Mark Jackson - +44 (0)7050 645590
europa-builder@ntlworld.com
http://harley.pcl.ox.ac.uk/~mark/Europa
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