On Sat, Dec 11, 2010 at 09:12:24AM -0800, Kirk Wallace wrote: > On Sat, 2010-12-11 at 17:53 +1100, Erik Christiansen wrote: > ... snip > > Adding a pull-down resitor to OK1's emitter, followed by the 3 spare > > CMOS gates, wired in parallel, will provide the required push-pull drive > > to C1. (And remove the problem of wasted gates.) > > Thanks Erik. I to study what posted, but it seems to put me back on the > right track.
A quick and practical way to check it out could be to try your circuit as-is. It'll quickly become apparent that OK1 can charge C1, but not discharge it, so the pump won't function. A pull-down on OK1's emitter would allow C1 to discharge, but only slowly, since the value cannot be too low or OK1 can't pull C1 high any more. However, add the spare gates as buffer, and you're cooking with gas. > ... snip > > > the input shorted to a supply. The .1uF C2 cap would show a ~2V spike > > > when I made the +5V DC connection, I get nothing with the .33uF C2. > > > > I'm not sure that I follow the details of this, but the basic charge > > pump already checks for DC input (i.e. loss of oscillation), including > > short to either rail. If C1 is not actively driven high and low, then > > there is no output. > > The circuit works properly to detect non-AC input. It's just when the +5 > input is connected, there is a one pump charge that gets through which > is large enough to bring the output cap up a couple of volts in a spike. > I am concerned that when the machine power is turned on and there might > be a glitch on the output. A slightly larger output cap absorbs the > glitch, but cap also charges up well enough with real AC input (or more > than one pump in a row). Ah, now I see. Yes, the circuit needs to be dimensioned to provide that discrimination, if it is to work. One pulse must never be enough to reach the detection threshold on the schmitt trigger or other comparator on the output. So C2 can be made significantly larger, and without going to electrolytics, which someone deprecated. 2uF ceramic SMD caps are tiny and cheap. Bang several in parallel, if desired. The discharge resistor controls how high a pulse frequency is needed, more than single pulse immunity. That's controlled by the C1/C2 ratio. Consider the charge Q tranferred from C1 to C2 on one pulse: C1*V1 = Q = C2*V2 If C2 = 10*C1, then V2 = V1/10 , minus diode drops. So you could use schottky diodes, if inclined, do reduce diode drops. But if you use CMOS, which has a much larger output voltage swing than the LS device I think I've seen mentioned (And I'd not consider using here), then ordinary silicon diodes will suffice. Hopefully that'll further help avoid the need to figure it all out the hard way. (Just yell out if too many details are spoiling the investigative fun. :-) Erik -- Most OpenBSD mailing lists strip messages of MIME content before sending them out to the rest of the list. If you don't use plain text your messages will be reformatted or, if they cannot be reformatted, summarily rejected. - http://www.openbsd.org/mail.html ------------------------------------------------------------------------------ Oracle to DB2 Conversion Guide: Learn learn about native support for PL/SQL, new data types, scalar functions, improved concurrency, built-in packages, OCI, SQL*Plus, data movement tools, best practices and more. http://p.sf.net/sfu/oracle-sfdev2dev _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
