Electronic Boost Control

[FJB203 at aol.com]

In a message dated 97-04-02 18:26:29 EST, you write:

> My first query is to a power supply to produce a clean 5V from the 
>       dirty 12V supply of a running engine. Does anyone have a schematic of

>       a typical power supply which may be used for such an application, be 
>       it switch mode, linear, or whatever? I will need to drive a 12V pulse

>       solenoid valve, so will need sufficent curent to run driving
circuitry 
>       for this valve (I expect that this will be biggest current demand on 
>       the system)

For linear you can use a zener diode in conjuction with power transister
(bipolar) or certainly a LM7805 or equivilent (with very few external parts,
two caps and a diode). Feel free to email me directly and I'll dig out the
schematics I have :)  Second, for higher current applications (over an amp or
so), Linear circuits might not be the way to go, therefore you could build a
switching power supply.  I have a schematic for that as well in a book I
purchased from Radio Shack (which has all of the theory, linear and swithcing
schematics I mentioned) and its about $10.  The theory is helpful if oyu have
the urge :).  THe book is called "Designing and building power supplies".

>       My second query is in regards to the driving of the valve. It uses a 
>       12V coil which requires around 800mA holding current. Does anyone
have 
>       any recommended methods to drive coils like this from a logic output?

Yes, this is very easy.  Depending on how fast you need it to switch, you
could use a bi-polar transistor (2n2222 does 800ma no problem), and the
2n3055 NPN bipolar cranks 3A with a small heat sink (TO3 case)  If you want
extremely fast switching, you can use a MOSFET, which are also fairly easy to
drive.  Between a MOSFET or BIPOLAR you would use a 1k-2.2k resistor between
the switching lead and the TTL/CMOS circuit.  Drop me a line and I can give
you more details :)

Fred