Post by Van Horn, DavidWhat's the rated voltage of your switching element?
Currently I am using a 40V MOSFET and a 33V 5W Zener, and I was wondering
if a Transil would have a sharper knee, or better reliability.
Post by Van Horn, DavidThe point is to let the voltage rise, but not high enough that it fails your transistor.
Yes. The higher the voltage, the more the energy will be dissipated, but
it will happen out of the injector and thus the magnetic field will collapse
faster.. right?
Per contra, the zener will produce considerable heat, as it will be the one
that will dissipate the "injector closing" energy. That's why I think this
component is so critical.. and I would like to replace it with a Transil
(the hint is that as the high voltage flyback diode will work only for a
short part of the duty cycle (just at injector closing), a transil may be
possibily better because it seems more suited than a zener for "peak work",
while zeners are characterized for continuous work.. but I may have written
a lot of silly things, I don't know.. that's why I am asking).
Post by Van Horn, DavidThere are FETs with zeners from the drain to the gate for this reason,
but that keeps the transistor on and keeps energy going into the load.
Yes, an external component here is necessary. I just don't know if changing
the zener to a transil would be a good thing or not, and as both will work,
the difference may be noticed only after hundreds of hours.. hence it's a
job for the theory / knowledge / experience, which some of you certainly
have.
Cheers,
Mario
Post by Van Horn, David-----Original Message-----
Sent: Monday, December 18, 2017 11:47 PM
To: Microcontroller discussion list - Public.; Microcontroller
discussion list - Public.
Subject: RE: [OT] Any nice IC to directly drive at least 4 relays?
Post by Van Horn, DavidThe diode across the coil method isn't the best either, if you care how
quickly the relay opens.
Slow opening can result in contact welding.
The best method is a Zener from Collector/Drain to ground. Set the
Zener voltage a bit below the transistor VCE/VDS rating.
This speeds up the collapse of the current in the coil by as much as 3x.
Interesting. Going from relays to high impedance (12 ohm) fuel
injectors, a zener would make it close faster, I guess?
And, in this application, would it be better a 33V 5W zener or a 33V TVS?
I'm not sure how I would "size" the TVS, though, as they're usually
rated for peak power. I have some 33V SMB size ones rated 600W peak
power but I have no clue what continuous power they would reliably
work on (well, an injector closing is not "continuous" per sé, but I
need to know if the TVS diode can withstand that).
Is there an "experience rule" to quantify/translate peak TVS power to equivalent Zener power?
Besides this, what are the difference between Zeners and TVS? AFAIK
the latter have a sharper knee and are generally much faster, but I'd
like to hear from the experts.
Cheers,
Mario
--
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
--
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
--
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist