I have gotten away with using a transistor on the anode side driven by a 4N35 optocoupler just for the sake of doing the experiment. The 4N35 then isolates the logic from "the high side".
There's a little experiment of mine that uses that technique in order to operate the bi-quinary tubes. The "1" bit from the 74141 controls two 4N35 optocouplers which select the tube's front screen or back plate as the active anode. Then, the bits 2,4,8 operate normally on the cathodes. It's just an experiment to do, to show one method to isolate from the +175 volts. I know there are other better methods. Chuck > > >---- Original Message ---- >From: [email protected] >To: [email protected] >Subject: RE: [neonixie-l] Re: Using transistor as anode switches >Date: Sun, 13 Mar 2011 16:43:17 -0700 (PDT) > >>I'm not the best to explain transistors, but if you use discrete >>transistors and you are multiplexing, remember to clamp the cathodes >>to a higher-than-ground voltage. I've had grief with ghosting, and >>after all that soldering I may just use integrated driver chips. >> >>On Mar 13, 5:09 pm, David Forbes <[email protected]> wrote: >>> On 3/13/11 12:31 PM, ggtnuminix wrote: >>> >>> > I have been reading Jason Harper's article on driving nixies >with >>> > discrete transistors. I understand the portion of using a MPSA42 >to >>> > control the cathode side of a nixie; however, I dont understand >why >>> > you couldn't use the same approach to control the tube anode. >Most of >>> > the designs seem to use a MPSA42 and MPSA92. >>> >>> The Nixie tube has two voltage levels to which your logic needs to >exert >>> control. The cathodes are connected by transistors to the low >voltage >>> (ground), and the anodes are at the high voltage of 180V. >>> >>> A transistor's base, its logic input, must be at the same voltage >>> (within one volt) as the emitter, which is connected to either >ground >>> for the cathode or to 180V for the anodes. The reason is that the >base >>> and emitter are connected internally by a diode which conducts >current >>> and has that 0.7V voltage drop that you read about. >>> >>> The logic circuits all run near ground, so they can be connected >>> directly to the transistors which control the cathodes. But if you >>> connected the logic signals directly to the transistors at the >anodes, >>> then there would be 180V passing through the transistor's base >into the >>> logic circuits. This would destroy the logic circuits immediately, >as >>> they can only handle about 5V. >>> >>> The MPSA42 transistor is needed to provide a path for each anode >control >>> signal to be translated from the 0V level to the 180V level that >the >>> MPSA92 anode transistor bases require. >>> >>> -- >>> David Forbes, Tucson AZhttp://www.cathodecorner.com/ >> >>-- >>You received this message because you are subscribed to the Google >Groups "neonixie-l" group. >>To post to this group, send an email to [email protected]. >>To unsubscribe from this group, send email to >[email protected]. >>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 [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/neonixie-l?hl=en-GB.
