Hi Neil,

OK, solid state relay is something different I think... they are a drop in =
replacement=20
for a relay and switch AC or DC and provide isolation, and are coniderably =
more=20
expensive than a relay (but offer the advantages of silent operation, longe=
r life, and=20
lower drive current).

On the other hand an Intelligent MOSFET, smart high side driver, or other v=
ariation=20
of these names, is DC only, consists of a N-ch MOSFET switch and supporting=
=20
circuitry to do high side driving and a bunch of protection features such a=
s over=20
current, over voltage, under voltage, over temperature. Some have diagnosti=
c=20
feedback.

http://www.mouser.com/Search/Refine.aspx?Keyword=3Dvnq690

VNQ690SPTR-E USD3.91 each 500+, so if your quantity is up there then it's i=
n the=20
ballpark. One device replaces 4 relays. They nicely handle the clamping of =
inductive=20
loads at switch off, so you don't need any suppression components (although=
 you=20
do have to consider the energy being clamped and associated power dissipati=
on).

As Russell noted, they do what they say they do in terms of handling short =
circuit=20
etc, which is nice... typically no need to put a fuse on each output. More =
or less=20
bullet proof for most low voltage DC applications, but not appropriate for =
use where=20
a potential fault could see mains AC power applied to an output.

In the comparison the main advantages of a relay are isolation, AC switchin=
g=20
capability, and often price as well.

On 8 May 2011 at 6:34, PICdude wrote:

> Not sure what an "intelligent MOSFET" is, but you're linking to a =20
> solid-state relay.  These specific ones don't seem to be available =20
> from my usual sources (Dk, Mous, etc), but other solid state relays =20
> are in the US$25 range, and that's a significant jump from MOSFET's, =20
> transistors, or relays at ~$1 each.  With several of these in each =20
> unit, the price diff is significant.
>=20
> Cheers,
> -Neil.
>=20
>=20
>=20
> Quoting Brent Brown <brent.brown@clear.net.nz>:
>=20
> > Would you consider "intelligent" MOSFET's? Would give you a space savin=
g over
> > relay, but possibly more expensive. One I've recently used (for  =20
> > driving solenoids) is
> > the ST Microelectronics VNQ690SP, 4 channel high side solid state  =20
> > relay, nominal
> > 10A, 36V, fully protected.
> >
> > http://www.st.com/internet/automotive/product/75329.jsp
> > http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERAT
> > URE/DATASHEET/CD00003299.pdf
>=20
>=20
> --=20
> http://www.piclist.com PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>=20

--=20
Brent Brown, Electronic Design Solutions
16 English Street, St Andrews,
Hamilton 3200, New Zealand
Ph: +64 7 849 0069
Fax: +64 7 849 0071
Cell: +64 27 433 4069
eMail:  brent.brown@clear.net.nz


--=20
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.