Re: Initializing a Flip-Flop on Power-up

On Fri, 17 Feb 2006 21:47:31 +0100, Frank Bemelman wrote:
"Joerg" <notthisjoergsch@xxxxxxxxxxxxxxxxxxxxx> schreef in bericht
Hello Rich,

And an "R" or an "S" input doesn't need a lot of noise immunity -
once it's reset, it's reset! ;-)

Ahem, if it's not a Schmitt input then rather bizarre things can happen
when applying the ramp of a slowly charging cap. Stuff like both Q and
/Q being high at the same time and occasionally that is followed by
something that can't take that and croaks. Like an H-bridge.

Yeah, and the H-bridge was in charge of keeping the sattelite in orbit.

Did any of you guys even read the original question?
-----<quote>-----
From: Dan Charette <dan@xxxxxxxxxxxxxxxxxxxx>
....
I've got a small toggle circuit that I'm using to drive a shutdown
circuit on an audio power amplifier. The circuit is made from a CD4093
Schmitt trigger NAND configured as a debouncer for my mute switch input.
The output of the 4093 is fed into a CD4013 fo provide toggling
cabability. I've got S and R tied directly to ground. But, I'd like to
explore the possiblity of providing a predictable power-up scenario.
Currently, the circuit upon power up will default to one state or the
other. What are some methods that you fellas have used to achieve a
known state consistantly with a flip-flop like this when the power
supply is from a single source. First gut instinct that I'm thinking is
to make some sorta RC timing circuit on the power supply pin so that I
can provide the set or reset pins with something known before the power
supply pin comes up. Any thoughts? Also, I don't want to add too much
additional circuitry... if I can solve this purely with passive
components or a few transistors, that'd be great.
....
----</quote>-----

i.e., a small cap from Vdd to R, and a 47K-100K from there to Vss.

If you want to be persnickety about it, then Dan could see if there's a
spare gate in his 4093

Or, better yet, put the R/C on one of the 4093 inputs - I'd have to see
the existing circuit to see if that's doable.

Thanks!
Rich

.

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