It looks to me like you're getting "0V" out when the input is -24V and +5V out when the input is greater than -(24-Vz) (i.e. non- inverting, as Jim indicates).
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18 years ago
-- Keith
Intermittent Problem with Circuit Design. Asking for Assistance.
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18 years ago
Didn't you want the opposite? Your circuit is non-inverting. Jim's is inverting (and simpler; no zener needed).
It happens. ;-)
-- Keith
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18 years ago
...
D'oh!
Yes. I got it back-asswards: Here's an excerpt of the OP: " The kicker is that at -24VDC it needs to be converted to +5VCD, and at -12VCD, it needs to be at ground."
Yeah, looks OK to me, except of course, I have to futz around with everything:
Cheers! Rich
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18 years ago
That doesn't look like any circuit anyone suggested to you. Where is the 12V pulse coming from exactly?
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18 years ago
You need to watch pulling logic inputs negative. Since the application requires no gain, a simple level level shift with over/under-voltage protection is all that's needed: View in a fixed-width font such as Courier.
. . . . . +5V . | 74HCT14 . -12 --- [10k] -- 5 . | 20VZ | |\\ | . | ---|>|--||--+---| o--- | . | / 1N914 1N914 | |/ | . -24 -- | --- 0 . [100k] . | . --- . gnd . . . . .
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18 years ago
Ohh, 5V BVebo. Ouch! ...wasn't considering reality. ;-)
Maybe the common base configuration is a good idea. Thanks.
-- Keith