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From: "John Jardine"
Subject: Re: True output current capability of 4000 series CMOS
Date: Sun, 19 Jan 2003 21:30:15 -0000
NNTP-Posting-Date: 19 Jan 2003 21:15:54 GMT
X-Newsreader: Microsoft Outlook Express 5.00.2615.200
Gibbo wrote in message
> We all know what the spec sheets say. Varies but 1mA is common
> My techie didn't believe it and insisted it was much higher as a result of
> circuits he had built whilst learning. I told him to stick to the specs as
> as any commercial designs were concerned.
> About 2 1/2 years ago he built a circuit in the workshop. 2 gates of a
> an oscillator at around 1Hz. The other 2 gates forced high and low with
> outputs powering red LEDs via 1K. The output of the oscillator provided
> to another 4011 oscillator running at around 100Hz (so it was gated and
> by the first one). Output of the 100Hz osc powering a red LED via 470R.
> gates of the 2nd 4011 forced high and low powering red LEDs again via 1k.
> powered it up and all levels were *well* within the required range. For
> instance the osc output driving the red LED (via 470R) from VDD (12 volts)
> pulling down to less than 1 volt. He then hooked it up to the large 12
> battery and kept his eye on it for a few weeks then it got forgotten
> Last week we moved the workshop round and found this thing hanging off the
> of the battery bank. Still there, still functioning perfectly. The output
> current is somewhat outside spec to say the least.
> So what is the *real* output capability of these things ?
In this instance there isn't one that can be defined, as it's a case of
horses for courses.
The outputs of the CD stuff simply look like a purely ohmic resistor of
maybe 300ohms to either of the rails.
Load a logic high and the output voltage simply drops off the more that
current is taken out of it.
If not needing the defined logic voltages to drive other logic gates then
you can without particular harm, pretty much flatten a CMOS o/p voltage as
current is pulled from it.
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