From: "Frank Bemelman"
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Subject: Re: How to get CMOS counter to drive a relay?
Date: Wed, 23 Oct 2002 17:49:04 +0200
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Organization: EuroNet Internet
NNTP-Posting-Date: 23 Oct 2002 15:49:48 GMT
"Winfield Hill" schreef in bericht
> Tony Williams wrote...
> > Frank Bemelman wrote:
> >> Okay, found another 4060. Relay from output to ground,
> >> no diode. Vcc = 18V. Outputfrequency is 25Hz, and the
> >> relay is clicking like mad. The undershoot is 1V below
> >> GND, or 0.7V with diode. Voltage drop from the output
> >> is 5V, so the relay gets 13V. [snip]
> >> The 4060 is now running at 28,5V, relay draws 40mA,
> >> no diode. Oh, and no decoupling cap, and long wires ;)
> > Thanks Frank. Strange..... I'd have laid odds that
> > throwing a pin below the substrate would have stopped
> > the ic from operating, and blown it earlier.
> If the current forced into a CMOS pin, whether Vdd or Vss,
> is high enough, the chip will go into SCR latchup. In this
> condition it shorts out the supply rails with about a 1.0 to
> 1.2V drop, and the SCR is able to carry several amps if the
> power supply insists on delivering it. Of course, the chip
> 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.
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