Re: [TCML] op amp wiring

[DC Cox <resonance@xxxxxxxxxxxx>]

First, don't use the 555 to drive a 2N3055.  This design is not robust
enough to do the job.  Use a single transistor BUF420M (Digi-Key).  It rated
something like 60 Volts at 30 Amps and will almost never blow.

Fuse the DC part of your circuit also.  Use a fast acting instrument fuse so
any shorting will blow a fuse and not your component.

Be very careful if you elect to use a MOSFET driver for a plasma sphere.
The MOSFET design is much more efficient and provides excessive current
on the HV output of the flyback --- enough to burn thru the stem of most any
globe if not controlled.  With our MOSFET design we always use some 10 kV
100 meg resistors in series with the output to prevent this.  Personally, I
prefer the BUF420M design as it delivers approx 1 mA to the globe --- not
enough to burn the stem thru.

Be sure to use a "gapped core" flyback to prevent excessive sec current.  I
gap at 4 mils on each side of the core.

Dr. Resonance






On Fri, Jan 16, 2009 at 12:56 PM, Weinhold Shannon L <
Shannon.L.Weinhold@xxxxxxxxxxxxxxx> wrote:

> My apologies to Scott for leading this discussion towards my own ends,
> but I have questions for some of you gurus out there that are along the
> same lines as Scott's.
> I have been working for a while on building a variable frequency power
> supply for a plasma project I am working on.
> Its high pressure xenon in a long tube, and so requires a substantial
> amount of high frequency power to obtain a linear discharge clear
> through the tube.
> I've had some luck in ionizing the entire tube using drivers with a
> feedback on the flyback to get the transformer to work at resonance, but
> the effects in the tube are not what I'm looking for. In order to get
> them I need to be able to vary the frequency of the high voltage to the
> tube. The tube seems to exhibit these effects at some narrow bandwidths
> at about 20 and 40khz.
> So with much research and some trial and error (I have bad circuit board
> karma, they hate me, and the feeling is mutual, so getting a circuit all
> soldered together and working was a bit of a milestone for me) I have
> finally built a 555 driver with variable resistors that will oscillate
> at the frequencies I need.
> (as a side note, the duty cycle is at about 60%, is this a good match
> for a flyback?)
> The problem I'm having now is with mating the output to a transistor
> that is powerful enough to drive the flyback to the level I need. I keep
> burning up 555 when I get the resistance between it and the base of the
> transistors low enough to get the transistor switching.
> I was having some success powering the whole tube with the self resonant
> driver circuit using some old-school power transistors that I had
> recycled from some old circuit boards. Namely, the MJ150004. Then of
> course I shorted out the leads with 24 volts and a bunch of current and
> that was the end of that.  But that and the 2s5686 seemed to be working
> well until I destroyed them by being careless.
> Anyway, what I need to know is-
> How do I mate the 555 output to a large power transistor?
> Should I remove the flyback spacers with this sort of driver to get more
> power?
> Should I incorporate a voltage regulator into the 555 circuit, and if
> so, at what voltage?
>
> Any other wisdom that might be helpful is very welcome.
>
> Thanks all !
>
>
>
> Shannon Weinhold
>
>
> "The problems of today cannot be solved by thinking the way we thought
> when we created them."
> -Albert Einstein
>
>
> -----Original Message-----
> From: Scott Bogard [mailto:sdbogard@xxxxxxxxx]
> Sent: Thursday, January 15, 2009 2:17 PM
> To: Tesla Coil Mailing List
> Subject: Re: [TCML] op amp wiring
>
>
> Here is a picture of what I had in mind
> http://bogard.110mb.com/op-amp%20driver.bmp
> as you can see the beginning looks just like the standard 3055
> circuit, except the BJT drives the non-inverting pin, and the
> inverting pin is fed a steady 6 volts.  This should give a square wave
> output to feed the MOSFET.  If this won't work, I can always drive a
> BJT which would drive the MOSFET like is done with the 555 timer
> schematics.  Let me know what you guys think.  Thanks.
>
> Scott Bogard.
>
> On 1/15/09, Gabriel Cardona <cardogab7341@xxxxxxxxx> wrote:
> > Scott,
> >
> > Driving a power MOSFET from an op-amp is not recommended. Power
> MOSFET's
> > require about 10V higher voltage at the gate than the source to be
> fully
> > turned on, and there is a significant amount of stray capacitance on
> the
> > gate that needs to be charged before the gate voltage will get to that
> 10V
> > above Vsource. Op-amps typically cannot supply the instantaneous
> current
> > required to drive a power MOSFET gate. You can use the op-amp to drive
> a
> > MOSFET driver. It looks like you are using the op-amp as a comparator,
> you
> > may want to look at a stand-alone comparator such as the LM111 or
> Linear
> > Tech LT1011. You will still need a MOSFET driver after the comparator.
> >
> > Regards,
> >
> > Gabe Cardona
> >
> >
> >
> >
> > ________________________________
> > From: Scott Bogard <sdbogard@xxxxxxxxx>
> > To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
> > Sent: Thursday, January 15, 2009 11:22:08 AM
> > Subject: Re: [TCML] op amp wiring
> >
> > I'll put a schematic up someplace later it may be some time as I don't
> > have internet in my apartment and school internet frowns on uploading
> > files; but basically this will be a modification of the single
> > transistor feedback winding schematic, the op amp will have a steady 6
> > volt fed the the non-inverting pin? and the sinusoidal output (which
> > would normally be the base for the 3055 transistor) will go to the
> > inverting pin?.  The idea is to have the op amp flip between 0 and 12
> > volts to drive a mosfet for a square wave output, when the mosfet is
> > on, it will choke the input to the inverting pin (via the feedback
> > winding) until the op amp switches off, and then the cycle begins
> > again when the field in the feedback winding dissipates.  This is
> > probably an over complicated system, but I want something that is
> > square wave and self resonant (the standard 3055 circuit seems to
> > never utilize the full 12 volts input unless I'm reading the
> > oscilloscope wrong, and I don't like the 555 timer circuits as they do
> > not dynamically adjust to load.)  Also as best I can tell nobody does
> > it this way and I wanted to make something original; then again maybe
> > they done do this because it won't work, I don't know.  Any help would
> > be appreciated.
> >
> > Scott Bogard.
> >
> > On 1/15/09, Gabriel Cardona <cardogab7341@xxxxxxxxx> wrote:
> >> Scott,
> >>
> >> Can you explain what you're trying to do?
> >>
> >> 1. What will the output of the op-amp be connected to and what
> voltage
> >> levels are needed at the op-amp output?
> >> 2. What voltage levels will be at the input to the op-amp?
> >> 3. What is the op-amp you're using (manufacturer and part number)?
> >>
> >> With this information, it will be easier to help.
> >>
> >> Regards,
> >>
> >> Gabe Cardona
> >>
> >>
> >> ________________________________
> >>
> >>
> >>
> >>
> >> ________________________________
> >> From: Scott Bogard <sdbogard@xxxxxxxxx>
> >> To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
> >> Sent: Wednesday, January 14, 2009 1:17:51 PM
> >> Subject: [TCML] op amp wiring
> >>
> >> Hey guys,
> >>      I am in need of some assistance, I am doing an experiment with
> >> flyback drivers, and the circuit I designed uses a Op-amp in a
> >> comparator configuration.  The only problem is I know nothing about
> >> actually wiring an Op-amp except for the extreme basics (inverting
> >> pin, non-inverting pin, output) which I learned in school.  I do not
> >> know how to connect it to the power supply, if I need negative
> >> voltage, what the "offset" pins are for, what Vcc or Vss is, etc.
> Any
> >> help would be appreciated, there are 8 pins and I only know for sure
> >> what 3 of them do, thanks.
> >>
> >> Scott Bogard
> >> _______________________________________________
> >> Tesla mailing list
> >> Tesla@xxxxxxxxxxxxxx
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> >> Tesla mailing list
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> >>
> > _______________________________________________
> > Tesla mailing list
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> > Tesla mailing list
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> >
>
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