Pete, that's a nice application for the cascode circuit... Help me understand how it eliminates concerns about dead time and ghosting. Terry
On Thursday, February 26, 2015 at 3:05:55 AM UTC-6, petehand wrote: > > <https://lh5.googleusercontent.com/-_PML27wwc9w/VO7hHsuYRwI/AAAAAAAAATA/LVcwCOp5mWw/s1600/IN17.jpg> > I did mean to change R22 to 10k, but I can suggest an even better way. > This is a circuit I've used to multiplex IN17s, with no dead period and no > ghosting. It looks terrifyingly unsafe. Let me explain. > > When the processor pin is high, Q1 base-emitter voltage is 0 and the > transistor is cut off. The port pin sees no high voltage. When the port pin > goes low the transistor turns on as a constant current source, the current > set by (5 - 0.6)V/R2 or about 1mA. This drops 170V across Q1 and 10V across > R1, which turns on Q2. Q1 is operating in linear mode, not saturated, so it > switches in nanoseconds. Resistor R1 is necessary to help Q2 to switch off > rapidly. > > This configuration of Q1 with the implied transistor inside the MPU is > called a cascode <http://en.wikipedia.org/wiki/Cascode>. > > > > > On Wednesday, February 25, 2015 at 3:45:43 AM UTC-8, joenixie wrote: >> >> Hmmm... interesting observation Pete, are you talking about changing R21 >> or R22 to 10K? I chose 100K because I have them in my NixieNeon clock. >> >> -joe >> >> -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to neonixie-l+unsubscr...@googlegroups.com. To post to this group, send an email to neonixie-l@googlegroups.com. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/84001c02-dcda-4035-8be3-509a1c6328f1%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
