power supply

[Tony Bryant]

>   --L---D-------[7805]----- +5V
>       |   |  |         |  |
>       C   Z  EC        C  Z
>       |   |  |         |  |
>       -   -  -         -  -
> 
> Should this be enough?
> 
Works fine, until you try to start with a partially 
charged battery. If you are drawing any decent current
through it (>500mA), you need an exceptionally large
capacitor (6800uF isn't enough for 600mA).
The 7805 NEEDS to be on a decent heat sink.

I resorted to using a small battery backup in addition, which 
holds the voltage up across spikes, and the gaps in the ignition 
switch.

Also your input stage capacitor is going to be sucked dry in a
matter of microseconds, by the starter motor when you turn it
over. Try moving the diode before the cap.

If I do it again, I'll be using a switch mode DC-DC 
convertor chip.
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* "Insanity is the only sane response to an insane world" *
*                 >> bryantt at fp.co.nz <<                  *
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