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.
