Simple circuit for frequency adjustable on/off mosfet?

Thread Starter

clone477

Joined Oct 3, 2008
28
Hoping someone can help as I am really new when it comes to solid state electronics, have a long history or automotive electronic diagnosing though that helps somewhat.

What I am trying to do is have a variable frequency on/off switch to work in a 12vdc circuit that will be used to charge and discharge inductive coils. I am playing with Tesla circuits, and redirecting the HV discharge from a inductor into capacitors. I am just getting my feet wet learn and plating with this, very new at it, trying to learn.

Ideally something prebuilt would be nice, similar to frequency and duty cycle adjustable dc motor controllers? Do they exist prebuilt?

Other wise can someone guide me on what the paper transistor I should buy and how I can control it? Any advice is really appreciated, I have tried sourcing online and youtube, but nothing seems to be clear cut. Thank you all.

Fernando
 

AnalogKid

Joined Aug 1, 2013
9,185
Read up on the 555 family of parts. NE555, LM555, LMC555, etc. This is a simple oscillator chip that is very versatile. There are tons of 555 oscillator schematics online, and lotsa small modules and kits on ebay. Plus, I think there is a 555 tutorial on this site somewhere.

Adjusting frequency and duty cycle separately usually requires two timer circuits. IT gets tricky because the two values interact - 10% of a cycle at 10 Hz is much longer than 10% of a cycle at 1 kHz. Another way to go is to have two monostables in series, one for the up part of the cycle and one for the down part of the cycle. Now the two are independently adjustable, but adjusting either one changes the overall frequency. So you need to think through exactly what you want to be adjustable. There are many different circuits for this.

ak
 

Thread Starter

clone477

Joined Oct 3, 2008
28
Alright thank you, I will look at those, really a 50% set duty cycle is good, I really want frequency adjust though.
 
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