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Re: NE555 driven coil WAS:Re: SCR driver coil...



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.
Mike