Hi,

I used to be part of the list a while ago, but for one reason or another
I left :-(

Anyway, I have a strange power supply circuit that I need to protect and
its confusing me.
I have a 9V linear wall cube supply which is powering a 7905 -5V
regulator. The +9V from the wall cube is connected to the 7905 GND pin,
the GND from the wall cube is connected to the 7905 Input pin. This then
ends up giving me a +5V, 0V and -4V power supply.
This works fine, but I am conscious that if someone plugs in a power
supply greater than 9V I will get a larger negative supply rail voltage.
EG if someone plugs in a 24V supply I will get -19V!!!

I've been thinking about a simple zener to clamp the voltage and
probably a fuse too before the regulator.

Any suggestions? It's been confusing the hell out of me this afternoon.

Thanks for any help,

G
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