From: "Frank Bemelman"
References: <0001HW.B9CEF278023A90B81662EAD0@news.covad.net> <3DA9D6CC.email@example.com> <3DA9D9E1.firstname.lastname@example.org> <3DA9EE2A.B7CFD919@juno.com> <3DAAF96D.email@example.com> <3DAB71EC.DB68183C@juno.com> <3DAC2309.firstname.lastname@example.org> <email@example.com> <3DAFFA70.firstname.lastname@example.org>
Subject: Re: How to get CMOS counter to drive a relay?
Date: Sat, 19 Oct 2002 10:13:29 +0200
X-Newsreader: Microsoft Outlook Express 6.00.2600.0000
Organization: EuroNet Internet
NNTP-Posting-Date: 19 Oct 2002 08:15:40 GMT
"Winfield Hill" schreef in bericht
> Fred Bloggs wrote...
> > Winfield Hill email@example.com wrote:
> >> I'll edit your drawing to show the standard modern excellent,
> >> reduced-parts-count highly-reliable recommended small solution.
> >> 12VDC
> >> ---
> >> |
> >> +--------------+--------+--------+
> >> | | |
> >> | 1N4001 | _|_
> >> | --- | ) | |
> >> | / \ | ) | |
> >> | --- | ) | 20mA
> >> | | | ) | |
> >> | | +---+ |
> >> | | | \|/
> >> | +--------'
> >> ---+-----+ |
> >> 4060 | |
> >> | |--'
> >> Q +----||<-,
> >> | |--+ BSS138 etc
> >> ---+-----+ |
> >> | |
> >> --+--------------+--- gnd
> > This is bull. The BSS138 is a $0.33 item in small quantity from Digi-Key
> > and only available in SOT. It is a weak little thing with ~200mA Idc,max
> > and 360mW Pmax- sounds flimsy to me. Fairchild is apparently too ashamed
> > to include a datasheet link in the product folder.
> Oh yeah? Let's step outside and settle this like men. Bring a weapon
> of choice, TO-92 or SOT-23 at 40 paces. No TO-220, etc. allowed. :-)
> Hey, mine is a "modern" solution; you're still using massive ancient
> through-hole parts? Pick your FET of choice, whether TO-92 or SOT-23:
> 2n7000 or 2n7002; BS170 or BSS138; or Zetex ZVN4306A or ZXM61N03F.
> The latter part features Rds(on)max of only 0.22 ohms at 10V drive.
> But back to the classic BSS138, here's a serious FET with 30pF of
> input capacitance - that's no wimp. Fairchild, ON Semi, Infineon,
> Zetex and others present highly-detailed curves. With 5V drive this
> fine part can sink over 1A. It's rated at 3.5-ohm Rds(ON) max for
> 5V gate drive, and certainly is much lower at 12V. Assuming 3.5
> ohms, it dissipates under 1.0mW driving our OP's 720-ohm, 17 mA
> relay coil, and the 360mW rating exceeds the requirement by 370x.
> That's not bad for a common 5.2 cent part (Future, single reel) and
> nicely fits the need. Sorry, no bull there, just solid engineering.
Do we *really* need that fet for this 20mA relay ?
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