2N3055 Inverter

From:  Jim Lux [SMTP:jimlux-at-earthlink-dot-net]
Sent:  Thursday, May 28, 1998 10:20 AM
To:  Tesla List
Subject:  Re: 2N3055 Inverter

Tesla List wrote:
> ----------
> From:  gweaver [SMTP:gweaver-at-earthlink-dot-net]
> Sent:  Wednesday, May 27, 1998 6:51 AM
> To:  Tesla List
> Subject:  2N3055 Inverter
> I built a circuit using a 555 timer IC to drive a 2N3055 transistor at 60
> HZ.  I am using 12 VDC to power this device and the output goes to a 10:1
> step up transformer.  It won't work because the transistor won't shut down
> completely.  I need the transistor to go from 0 volts to 12 volts and back
> to 0 again but what I am really getting is 5 volts to 12 volts and back to 5
> again.
That is, the transistor isn't cutting off???  Do you have a resistor
(say 1K or thereabouts) from the base to the emitter? I assume the
transformer (load) is in the collector circuit?

This is a bit off topic, so you can email me off list..

> 5 amps X 12 volts = 60 watts, thats not enough to run a neon.  I have about
> 18 or so 2N3055 transistors.  Can I put several transistors in parallel to
> increase the power. 

You can, but you need to put a small (.1 ohm or so) resistor in series
with each of the emitters so that you don't wind up cooking a transistor
through current hogging: one of the transistors has a little better
gain, so it takes a little more collector current which makes it hotter,
so it has less emitter drop, so it takes a little more of the collector
current, which makes it hotter, etc.etc.etc.

Also, at high collector currents, a 3055 doesn't have a whole bunch of
gain (maybe 20-30). So, if you gang up a bunch in parallel, usually you
use another one as a driver in a sort of Darlington configuration. Check
out the high current DC power supply example in the Radio Amateurs
handbook for a bunch of design information on this sort of strategy,
including proper heatsink sizing.

Also, to run a neon at 450 VA, you'll need a pretty good sized
transformer to step up. That's 40 Amps or so at 12 Volts. A 40 Amp 12
volt transformer is big, heavy, and not cheap (unless you find it

Why not try one of the relatively inexpensive inverters designed to run
in your car. I have a 300W unit that draws about 30Amps from 12Volts. I
haven't tried it on a NST yet, there might be some weird interactions
from the highly inductive load and I might need to add PFC caps.

 I would like to have 1500 watts (that is 125 Amps at 12V!)
 but for now I will take anything I can get and worry about more power
> Will the high frequency feed back from the TC thourgh the neon effect the
> inverter?  Might need a filter circuit.

You bet it will, but, 3055's have almost no gain above a few kilohertz
(don't try building that HIFI amp with them), so oscillation is probably
not a problem. 3055's aren't real tough, and transients of only a few
hundred volts will destroy them in short order. You should put a hefty
zener across the Collector to Emitter to clip the transients.