Thank you all for those suggestions and the experiment to observe what actually happens when Vcc is disconnected from a 7441/74141 driver ic. I will be trying all of those very soon here.
Here is another curious aside that goes along with the 7441 questions. The 7441 does not blank hex codes A through F, as the 74141 does. I got to experimenting with an old 7441 in this mode. I had one connected to a binary counter that was counting single seconds. The 7441 then was operating the nixie tube normally for digits 0 through 9, and then it also was displaying the codes A through F. Here's what my old 7441s do for those codes: 1010 lights 2 and 8 1011 lights 3 and 9 1100 lights 4 and 8 1101 lights 5 and 9 1110 lights 6 and 8 1111 lights 7 and 9 It works great except that it appears to maybe exceed the total package dissipation of the chip, because after a while, one digit inevitably sticks "on" after running in this mode. So, even though the chip is built this way that it turns on two outputs simultaneously for codes greater than 9, it appears that it eventually destroys the ic. My guess is that having two outputs on at the same time is a bit more than the ic can handle. Anyone else know anything about this, or have any insight or opinions about it? Thanks, Chuck > > >---- Original Message ---- >From: threeneur...@yahoo.com >To: neonixie-l@googlegroups.com >Subject: RE: [POSSIBLE SPAM] [neonixie-l] Re: Yet more 7441, 74141 >questions >Date: Mon, 21 Nov 2011 12:58:38 -0800 (PST) > >>> the 7441/74141 having some path that would try to >>> draw excessive current from the inputs when Vcc is >>> disconnected. >>> >>> Is this a good idea to try, or is it a recipe for >>> trashing some HC160 counters? >> >>Its possible. The only way to really find out, is to run an >>experiment. Get one of your 74141s, and tie the gnd, and leave Vcc >>open. Connect a 470 ohm resistors to each input. Connect the other >>side of those resistors to its own DIP switch. A 4 switch DIP switch >>is needed. Tie the other side of the DIP switches to +5V. Gnd the >>negative side of your 5V source. Try all 16 input combinations, and >>see if there's a voltage drop across any of those resistors. >> >>The inputs of old TTL was usually the emitter of an NPN transistor, >so >>it would be reverse biased if you tried your scheme. Ideally, it >>shouldn't draw any current. But it may, if (1) 5V exceeds its >reverse >>breakdown rating; doubtful, or (2) there is some protection circuit, >>or phantom substrate structure. In old TTL, there usually wasn't any >>protection circuits, but a phantom diode is possible. Only way to >find >>out, is by experiment. >> >>If the input impedance is still high with no power, then your good >to >>go. However, if excess current is drawn. Excessive, being more than >>the HC160s are rated for, or higher than you want to supply, >whichever >>is less, then you got work to do. A possible solution (if needed) is >>to insert a schottky diode in series in each input path. Anodes >toward >>the counter, cathodes towards the 74141s. put 10K pull-up resistors >on >>each 74141 input. Tie the power side of those pull-ups to the VCC >pin >>of its nearest 74141. This is a pseudo-open-collector arrangement. >>Real TTL tended to have a soft pull-up. The 10K pull-ups will tend >to >>bring up into a safe Logic-1, when the circuit is powered. The >diodes >>will only allow the counters to sink the inputs to 0. When the >>counters output a 1, the diode is reversed, and off. The pull-up >will >>bring it to a logic 1. I suggest small signal schottky diodes, >because >>they have smaller forward voltage drops than your jelly-bean 1N914. >A >>logic 0 must be 0.8V or less. This may be iffy if a common silicon >>diode is used. A BAT46 will have a much lower forward drop. Probably >>~0.3V in this use. >> >>-- >>You received this message because you are subscribed to the Google >Groups "neonixie-l" group. >>To post to this group, send an email to neonixie-l@googlegroups.com. >>To unsubscribe from this group, send email to >neonixie-l+unsubscr...@googlegroups.com. >>For more options, visit this group at http://groups.google.com/group >/neonixie-l?hl=en-GB. >> >> $4.95/mo. National Dialup, Anti-Spam, Anti-Virus, 5mb personal web space. 5x faster dialup for only $9.95/mo. No contracts, No fees, No Kidding! See http://www.All2Easy.net for more details! -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To post to this group, send an email to neonixie-l@googlegroups.com. To unsubscribe from this group, send email to neonixie-l+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/neonixie-l?hl=en-GB.
