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Re: LED Charge Indicator

Original poster: Jan Wagner <jwagner@xxxxxxxxx>

Tesla list wrote:

Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>

At 08:18 AM 10/9/2005, you wrote:

Original poster: Jan Wagner <jwagner@xxxxxxxxx>

It's a bit "low tech" but you could use a neon glow tube (glimm lamp, guide light, ...). Just add multiple normal 1/4W 500Vmax carbon or metal foil resistor in series with the lamp, or just a single HV resistor, to keep the tube current down and below 1mA.

1mA and 20kV = 20W dissipation in that resistor... Sure you want to burn that much power? 

Well, as I said, keep the current below 1mA.

For an actual value, you'll have to check the ratings of the particular glow tube that you're going to use (NE-2, for example). AFAIK most of these small tubes are rated for the order of 0.1mA (100uA), at which they'll glow brightly. So that'd be what, ~2W overall resistor dissipation at 20kV? Typically 0.01mA works, too, though probably with a dimmer glow.

An untested idea: you could build your own optoisolator around a glowtube and a BPW77 visible light phototransistor. Add external supply, collector resistor, comparator (LM311, 50mA sink current capability), and a brighter indicator lamp (50mA rated <50V) or LED+series resistor if you insist ;-) Basically just a gimmick. The simple glow tube approach would be the more reliable one of these two, though probably not the most easily readable one.

- Jan