-----Original Message-----
From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf Of
Darren Gibbs
Sent: Friday, May 26, 2006 12:12 PM
To: Microcontroller discussion list - Public.
Subject: Re: [EE] solenoids and power transistors

>>I do have a snubber diode in the circuit,

>And the diode is rated for at least 2 amps right?
Good question..  I'm using a 1N4004
http://www.fairchildsemi.com/ds/1N%2F1N4007.pdf

Average Rectivied Forward Current = 1.0A
Non-repetitive Peak Forward Surge Current = 30A
Not sure which one of these is important 

Well what voltage does it clamp to with 1.6 amps?
(rhetorical...) it's about 1 volt.

>And the diode is FAST right?

I'm not sure how to tell...
>From the Motorola specs... 350 ns for 1.6 amps.

>And you are using a ballasted capacitor also right?
>(Because NO diode is fast enough!)

No caps in the circuit, but I'd love any suggestions for how to make this
work better. 

With your diode, you need to allow 1.6 amps via the capacitor for 350 nS.
Ballast resistor (In series with the capactitor) is the coil voltage divided
by the current.

 Seems like there's a consensus that a MOSFET makes more sense. 
 I'm about to try it.

 Oh! Yes, Power FETs are FAR superior! IMNSHO
(But you still need a correct snubber.)
As others have correctly said, "Pay attention to your grounds!"

>>they work fine when I switch back to using the smaller solenoid.

> Is the CURRENT the same for the smaller solenoid?

I'm sure not, I'll measure it and get back to you.

thanks!

darren

Tom

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