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Re: NE555 driven coil WAS:Re: SCR driver coil...
Tesla List wrote:
>
> Original Poster: Hollmike-at-aol-dot-com
>
> In a message dated 2/8/99 8:21:52 PM Mountain Standard Time,
tesla-at-pupman-dot-com
> writes:
>
> >
> > well I have built a coil this way before, I used a car coil driven with a
> > 555 timer, the draw back is the 555 timer is not leinar, when you adjust
> the
> > pulse width the freq changes, a better choice is a pulse width modulator,
> it
> > is easer to adjust to get the resonant freq out of what ever coil you are
> > driving, but you will kill it fast if you do not protect it, I used
one to
> > drive a high power transisor, you could use a fet, bjt or what ever
you are
> > used to dealing with...
> > kerry
> >
> If you put the output of a 555 timer into a 74124 one-shot timer, you can
> independently adjust the frequency and the pulse width(or duty cycle). The
> output of the 74124 is only 3 volts however, so you may have to run that
> through an amplifier (perhaps a 741 op amp) to operate the power transistor.
> I have used this, but used an optical relay driven by the one shot timer.
This
> required a diode across the relay due to the inductive load. There is only
> one disadvantage to the circuit above. You need a max of 5 volts Vcc for the
> 74124 and up to 15V for the other chips. Not too big a deal though.
Or, just use a 556 (dual 555) with one as the pulse rate generator and
the other with programmable width. Use a .01 uF cap to couple the output
of the first to the other. The negative spike from the falling edge of
the first triggers the second.
--
Jim Lux Jet Propulsion Laboratory
ofc: 818/354-2075 114-B16 Mail Stop 161-213
lab: 818/354-2954 161-110 4800 Oak Grove Drive
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