Controlling a NE2 lamp with a 12 V signal

Question

I have some NE2 lamps i want to control with a signal from my car. Signal voltage is about 11 to 14 volts and isn't very clean. I also have 170vdc available to power the NE2s. I plan on using these for turn signals and high beam indicator. Components must be able to be on for long periods of time. I would like to be efficient with power due to limitation of my 170v power supply.

I do have some TIP102's laying around but fear the input voltage is too low. Is there a 12v version of these? What resistors should i use to knock it down to the appropriate voltage? I cant find much data on these lamps and use.

Answer 1

To custom design a circuit to switch an NE-2 bulb directly from a 170V DC supply, you would need a transistor that can withstand the 170V supply voltage when off, and pass the 0.5 (or so) mA of current when on. The TIP102 you mention would have no problem with the on-current, but can only take 100V in the off state. To get some margin over that 170V you probably would want to use a transistor with a Vceo rated 200V (or better). This would be a relatively high-voltage, low-current kind of part, compared to the majority of parts that you'll find listed in Mouser or Jameco.

As an alternative, you might investigate using a solid-state relay to switch the high voltage under control of the typical 12V automotive signal.

Also, if you obtained bare NE-2 bulbs, be sure to put a limiting resistor in series with the bulbs. Ionized neon has very low resistance, so you need a resistor to keep the current under control. From 170V, using a 220K ohm resistor would give you roughly 0.75mA through the bulb, which would be a typical current for an NE-2.