AVR-Chat

Err. OK. By "Exactly correct" you mean that it isn't as you've shown it in your 
updated diagram at http://i5.tinypic.com/20hrl1i.jpg. Correct ?

You said that the wiring between the solenoid and your circuit is integrated in 
some way. I can't remember the details. If you provide 2 screw terminals (or 
similar) for the user to connect the solenoid and the connection to the supply 
is within your circuit/pcb/box, I would make that positive terminal "+12V", 
rather than "+12V In". ie. As you've drawn it.
You get D2 where you want it and the solution is conventional. All is good.

If however, you provide a single terminal and the user wires up the positive 
end of the solenoid, I would take D3 and put it facing the other direction in 
the negative supply. You get D2 across the load still and reverse polarity 
protection. The downside is if you have any external inputs that are ground 
referenced to this circuit, there will be a voltage drop across the diode. The 
other downside is that it is non-conventional. That means that someone else 
looking at it would scratch their head for a while. IMHO, you should avoid 
head-scratchers unless there is good reason to use one.

If that is the case, then you'd need to look at using a FET as a zero drop 
diode. Google should have something.

Steve.



On 20 Jul 2006 at 15:57, Ryan wrote:

> Exactly correct - the inductor is connected to +12V In.  D3 is for
> reverse polarity protection to the driver circuit.  D2 is supposed to
> kill any voltage spikes, but would be blocked by D3 as shown.  Therein
> lies the problem.
> 
> Hopefully this gets through ok, yahoo has been having problems with
> their site.
> 
> 
> --- In AVR-Chat@yahoogroups.com, "Steve Baldwin" <steve@...> wrote: >
> > Where's the problem ? > As you've drawn it, D2 is across the
> inductor. Just where it should be. > You said that the wiring to the
> inductor is integral to your unit so the only > place you can get the
> polarity reversed is at the "+12V In" node. There's no > hinderance
> there unless you have drawn the circuit wrong and the inductor > is
> connected to  "+12V In". > > Steve. > > >
> ========================================== > Steve Baldwin            
>              Electronic Product Design > TLA Microsystems Ltd         
>    Microcontroller Specialists > PO Box 15-680, New Lynn              
>  http://www.tla.co.nz > Auckland, New Zealand                     ph 
> +64 9 820-2221 > email: steve@...                      fax +64 9
> 820-1929 > ========================================= >

==========================================
Steve Baldwin                          Electronic Product Design
TLA Microsystems Ltd             Microcontroller Specialists
PO Box 15-680, New Lynn                http://www.tla.co.nz
Auckland, New Zealand                     ph  +64 9 820-2221
email: steve@tla.co.nz                      fax +64 9 820-1929
=========================================