555: strategies for series step-up transformers

From: Dominic-Luc Webb (dlwebb_at_canit.se)
Date: 12/08/04 

Date: Wed, 8 Dec 2004 11:23:33 +0100

Hi all,

My projects involve rectified 1500-2000 volt power supplies with only
modest power requirements, around 500 mW max.

I am interested in tying together identical transformers from the same
manufacturer to get kV power. I drive them with a working 555 timer
circuit running from a 9 VDC battery operating around 30 kHz, confirmed
on oscilloscope. The first transformer (0.5 Ohm primary, 50 Ohm secondary)
gives about 50 volt spikes. When I connect the second transformer in
series, voltage peaks drop to only a couple volts. I use a diode across
the transformer poles on the primary side of the first transformer, which
mainly has effect of making circuit more stable over time. I could mention
that the transformers appear to operate optimally around the 30 kHz I am
using.

Now that I have an oscilloscope, I know my 555 circuits work very well,
like textbook examples, but I also know that consistently adding NPN
transistors to the 555 output before the transformers seriously pulls
down the voltage output from the transformers. Thus far, without the NPN,
the 555 is not overheating, etc, so I would rather leave this alone.
Actually, I was thinking to maybe try opto-switches or a relay to power
the transformers from a series of 2 or more 12 volt batteries.

May I therefore ask for some suggestions about getting better coupling
from one transformer stage to the next? Circuit suggestions about
opto-switches and relays also welcome...

Dominic

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