power supply

[Terry Sare]

     Krister,
     
     Unless you have current limiting installed in line with either zener, 
     you will toast em' with the first spike that comes along. If not, the 
     coil will act as a fuse. Use a transorb or some form of surge 
     protection zener such a a 1.5KEXX (see Digikey catalog). I learned the 
     hard way, with lighting! Use bidirectional devices if available. 
     National makes a line of 3 legged regulators for automotive use.
     
     Terry
     


______________________________ Reply Separator ________________________________
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Subject: power supply
Author:  owner-diy_efi-outgoing at coulomb.eng.ohio-state.edu at dell_unix
Date:    7/16/96 3:35 PM


>Anyone out there have any solid simple cheap ideas for a 5V power supply for a
n
     
     
I'm making a simple ignition controller and would also like to get some 
opinions on power supply for automotive application.
     
I have made a simple one like this (hope it is readable):
     
     
  --L---D-------[7805]----- +5V
      |   |  |         |  |
      C   Z  EC        C  Z
      |   |  |         |  |
      -   -  -         -  -
     
The first L and C should filter most high frequencies, the diode and the 
large EC capasitor prevents sudden drops in voltage, and the first zener
( I have 22V) should ease up voltage spikes. The last zener is just in case, 
and it actually sits in the CPU board along with some tantal. capacitors.
     
Should this be enough?
     
  Krister Wikstrom
  kwi at mamma.icl.fi