Thanks guys! @David - In retrospect,common anode would have been nice, but they are what they are. They have such a neat color that I have never seen on an LED, I don't want to give them up! They make a really amazing glow on IN-18s.
@John and dr pepper - that all makes more sense now, thanks. If possible, floating the logic is always a fun way to go, but may make things a little more complicated (e.g. making a small mistake and frying something). I have some parts that are rated up to 15 and 20v, so I might try running them at 13v. I will have to mix and match tonight. I was thinking to use the level shifter on an H-bridge (4 transistor array [2 NPN and 2 PNP] that reverses polarity) to power NE-2s. While there are tricks to make one NE-2 light both electrodes, powering many requires a lot of components. Level shift the inputs for the PNP and use astable 555 and an inverter as the timer (adjust time base to minimize flicker and hum). Many NE-2s (with both electrodes lit) can be operated by adding lamps and resistors or am I still missing something? On Jan 19, 6:46 am, John Rehwinkel <[email protected]> wrote: > > When I connect the emitter to to +13v, base to ground or +5 through > > any resistor and collector to the array, it lights up. Only when I > > disconnected the resistor (open), does the array turn off. > > Right. You'd have to pull the base to +13V to turn it off. Something lower > (more negative) than +13V, such as ground or +5V will turn it on. We have > the same problem with anode drivers for nixies, but at 180V instead of 13V. > The usual approach is to use two transistors wired as a level shifter. > Pretty much any of the anode driver circuits posted in this group would work > for driving your LEDs too. > > > I have tried base resistors from 200 ohm to 200k ohm, and the same > > deal. When I use +5v on the emitter, however, the circuit works as it > > should. > > Yup, as long as the base is not more negative than the emitter, the > transistor will turn off. With the emitter at 5V, putting the base at 5V > will turn it off. > > In short, you basically need two transistors to do high-side switching like > this, unless you float your logic so that it's 5V supply is common with the > LED's 13V supply (note that then, the "grounds" must be separate, as your > logic ground will be at 8V, from the point of view of your LED's ground). > > - John -- 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.
