v multiplier circuit mod

[BrendanP]

I need to generate a reasonably high v for a project.

As a start for experimenting I'll use this.
http://www.armory.com/~rstevew/Public/StunGuns/dazer.htm

Looking at it it seems to me that I could do away with everything to the left of the primary winding in the schematic and replace it with a transistor under picaxe control and simply toggle the transistor on and off.

Can any see why this wouldn't work?

 

[Andrew Cowan]

Not just one transistor - two.

You'll want both an NPN and a PNP transistor (or a N channel FET and a P channel FET) to pull it high, then low. This is called a totempole driver. An example of this is a PICAXE output - it can sink or source. Just using a single transistor will mean the coil is connected/floating/connected etc. You will get a lot more voltage and power by pulling it high then low then high etc.

A

 

[hippy]

I'm no expert on analogue circuits but possible problems include ...

Q2 switching +V into the transformer primary may appear as a short, collapsing +V to a level the PICAXE is unable to operate at.

Back-EMF from the transformer onto the supply may cause problems.

Generated EMF may cause incorrect PICAXE operation.

Problems seen when operating servos and high-current motors will likely to be issues.

 

[Dippy]

Uh oh. The first PICAXE controller Taser?

Why not just get the PICAXE to 'switch' the circuit as-is?
Then you can keep power supplies separate.

 

[BeanieBots]

Taser. AKA microprocessor scrambler. Good luck.

No need for the transformer either. The circuit after the transformer is a series of capacitor/diode voltage doublers. You could just increase the number of sections. Alternatively, you could do away with that section and just use a pulse transformer. Either way, it won't be long before we see a post along the lines of:-
"Why does my PICAXE keep reseting" or "why won't my PICAXE download any more".

Dippy's idea is probably the most sensible.
Keep the circuit as is. Use a PICAXE to turn it on/off via a suitably rated relay with plenty of decoupling on the PICAXE side and some ferrite beads on the leads to the relay coil.

 

[BrendanP]

Thanks guys, I'm on Mouser at the moment ordering the parts, I'll get the Q's recommended and go with that.

As for my picaxe not resetting etc etc. I've got litteraly dozens of them here, if they get fried I cut them in half with side cutters to vent my rage on them and get another out.......

 

[Dippy]

IMHO good circuit design is cheaper than popping PICAXEs?

My first to-do would be to make a working HV circuit and see how much noise is coming out and then see how much noise gets induced into a circuit nearby.
Keeping the HV circuit and PICAXE circuit power supplies separate will minimise the noise but HF can sneak in all over the place.
Hence BB's suggestion for decoupling.

But, in any event, you'll find out soon...

 

[demonicpicaxeguy]

you could maybe consider optically isolating the picaxe and the hv circuit

 

[inglewoodpete]

Frying the PICAXE is not really the problem. Having it constantly or randomly resetting (restarting) due to dips in the power rail is the problem. Dips in the power rail can be caused by surges in the transformer primary due to increased demand or by heavy secondary current induction due to discharges.

You will need to isolate the PICAXE supply as much as possible from the transformer/secondary circuits. Ensuring that the 0v paths for the PICAXE, primary and secondary circuits do not carry each other's currents will help. A separate power supply feeding a 'tank' capacitor via a diode will also help for supplying the PICAXE.

 

[nbw]

safety goggles, defib, RCD protection, all the usual precautions... ;-)