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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> <email@example.com> <3DB1869F.649A02A4@bellatlantic.net> <firstname.lastname@example.org> <email@example.com> <firstname.lastname@example.org> <email@example.com> <firstname.lastname@example.org> <email@example.com> <firstname.lastname@example.org> <email@example.com> <firstname.lastname@example.org> <email@example.com>
Subject: Re: How to get CMOS counter to drive a relay?
Date: Thu, 24 Oct 2002 21:17:08 +0200
X-Newsreader: Microsoft Outlook Express 6.00.2600.0000
Organization: EuroNet Internet
NNTP-Posting-Date: 24 Oct 2002 19:17:22 GMT
"Frank Bemelman" schreef in bericht
> "Winfield Hill" schreef in bericht
> > will get very hot. But if the supply current limits at say
> > 750mA or so, the latched chip won't be too badly damaged and
> > will work properly again after the supply is cycled off - on.
> > When I began working with cmos in the late 60s, the spec for
> > incurring SCR latchup was only 20mA, and latchup was not
> > uncommon. A simple slip of a probe could trigger it. In
> > the last 30 years manufacturers have been careful to reduce
> > the gain of the parasitic transistors responsible for SCR
> > latchup, so the spec is now closer to 50 or 60mA, and actual
> > latchup onset may occur at even higher currents, say 100mA.
> > Frank subjected his poor suffering 4060 chip to only 40mA
> > flyback current, far below 60 or 100mA, etc. I respectfully
> > suggest that he try running three or four relays in parallel,
> > that should do it nicely. If the IR-drop from powering four
> > relays doesn't get his stubborn 4060, the flyback-triggered
> > SCR latchup will. :-)
> The output resistance seems to be ~200 ohm, so with 100mA there
> is 2 watts of dissipation, I'll try that. I don't have more
> of those relays, but I'll find a nice inductor + resistor
> combination to make it draw 100mA at 28V and see what leads
> to the quickest destruction.
I paralled the relay with 82 ohm. The 4060 at 28.5V now gets
pretty hot, but still touchable. The output drops to 5V and
the 4060 delivers 100mA. (50% duty cycle). Got bored after
an hour, and put a large choke parallel. The 4060 immediately
showed a latchup condition, and I could not turn off the
supply quick enough; it died under my hands.
I'll leave the room for an hour now, so you guys can debate
whether it is 'safe' to connect small relays to cmos-outputs
without any precautions ;) The 'test' shows it not so easy to
blow a regular 4000 cmos output.
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