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[on:]

I'm trying to get around 400v DC output, I'm using a 555 for a square wave which powers a transformer. I've tried a few transformers that I have which have come out of other things like wall socket dc adapters and old radios ect...
The problem is when I feed the power into the transformer I cant read any voltage output on my multimeter. (I tried both sides on each transformer because I wasnt sure of the primary and secondary windings).
I have my 555 set in astable mode an tried very high frequencies from aprox. 40,000Hz to low at around 10Hz.
My power input is a 6v rated (250mA) dc power adapter (which seems to read 9v+ on the multimeter).
Ive attached an example of the kind of setup I have .. I tried using a 2n3055 transistor instead aswell.
I cant figure out what i'm doing wrong?! any ideas?

[Reply #1 on:]

If you are using a NPN transistor it would work better as a low side switch for the primary winding of the transformer, wired emitter to ground, collector to primary winding, other primary terminal to +Vcc, and probably could use a series base current limiting resistor from the 555 output to the base terminal of the transistor.

Second, transformers have a specific frequency response determined by the core material used, so you need to keep the switching speed compatible with the frequency response of the transformer, 50/60 hz for power transformers, 1Khz for audio transformers. Also because you want to step-up in voltage you have to use the windings with the fewer turns for the primary and the windings with the higher turns count as the secondary. You are going to need a transformer with a very high turns ratio to get 400 volts out of a 9 volt input. like 1:1600 if memory serves me right (voltage ratio = square root of the turns ratio ? )


Lefty

[Reply #2 on:]

You might want to look at some proven circuits. Geiger counter HV circuits are all over now.
Sparkfun has a simple one with a transformer (see schematic) . . .

But one I really like that uses a 555 and a small inductor is here.
It provides an adjustable and regulated 200-500V.

[Reply #3 on:]

You also want to rectify the output of the transformer with a diode or better yet a diode bridge and then put a capacitor across it and then measure the DC output. Cheap (and not so cheap) multimeters are not good at reading high frequencies with funny waveforms, which is what you have.