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Can someone help me out please?

Discussion in 'General Electronics Discussion' started by Canabian, Mar 8, 2012.

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  1. Canabian

    Canabian

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    Mar 8, 2012

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  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    The recommended transistor is a darlington, you might be able to replace it with a mosfet, but not with such a low gain transistor.

    Beware diminishing returns, doubling the number of stages may yield poorer performance than you calculate.

    Why do you want to change the transistor anyway?
     
  3. Canabian

    Canabian

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    Mar 8, 2012
    Wow thanks for the quick reply! Well I wasn't sure if the BD 679 would handle doubling the output stages or not TBH... Is there a more effective way of doubling or at least increasing the output of this circuit? I sincerely appreciate your help. Correct me if I am wrong (PLEASE) but is a darlington not just essentially a "pair" of transistors? Hence Darlington Pair? Thanks again!
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    The doubling of stages will not require a change in the transistor.

    Yes a Darlington is a pair of transistors, it has much higher gain because of this.

    Look at the circuit. It claims 20kV, but this is across 4 capacitors with a combined rating of 1600V. Whilst I might believe 2kV, I wouldn't believe 20kV.

    You also have to worry about the diodes which have a combined inverse rating of 8000 volts, again, well under 20kV.

    Let me tell you a story...

    I once had the board from a negative ion generator. It took the mains and used a circuit similar to the multiplier in this one to produce a very high voltage. I believe the multiplier had about 15 stages or something. I powered this from the AC generated by an inverter used to charge flash capacitors (capable of around 400V). I ended up with a device that could pull arcs of almost a cm, but that you could touch without actually feeling them (you could get a circle of people to hold hands and have two of them pull arcs from each other). It was nothing like a stun gun. Some people found it mildly uncomfortable, but that was about it.
     
  5. Canabian

    Canabian

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    Mar 8, 2012
    Thanks Steve!

    Muchly appreciated! I hate to correct someone who so obviously knows MUCH more than me,but if you take a second look at the schematic it shows 8 caps at 400V each...3200V I know that this is still nowhere near the claimed 20kv and you are obviously right about everything else as well.

    So this leads me to my next question...Do you know of an effective yet simple to construct circuit that would provide what I am after? I have looked for stun gun circuits, but they are all very poor designs...80 - 90% of them being modified camera flash circuits... These are absolutely useless 1 shot devices. No good for my purposes.

    I am after something that would make a bear hit the floor basically...non lethal, but temporarily debilitating. I need to finish this project ASAP. Thanks again!

    ***Would I simply be able to use higher rated caps, and parallel some IN4007's (To increase inverse rating) to acheive what I am after?***

    *****Size/weight is a slight concern as well*****
     
    Last edited: Mar 8, 2012
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    yes, but if you look at the circuit again, you will note that 4 of them are in series across the output. Thus each of them has (about) 1/4 of the voltage across them -- 1600V would be the combined rating.

    I guess you need to tell us what your purposes are.

    You need to look at something like a tazer. I would expect that if it can drop a bear then it will almost certainly be capable of killing a human.

    Is there a bear lurking outside your door?

    the diodes can handle 1kV, so 1kV capacitors are likely to be a good idea.

    The problem with this circuit is that it steps up the voltage, but the current goes down.

    Circuits I've seen build up a high voltage across a capacitor (say 300V) and then quickly dump it across another transformer to produce a very high voltage, high power pulse. You're not going to get that from this circuit.

    that will mostly come from the batteries.
     
    Last edited: Mar 8, 2012
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