MOSFET Question

[Farlander]

Hey guys

I know a mosfet is required to be able to pulse high current.  The question now that I've built my pulse generator is, how do I wire the fet?  My circuit board uses the LM324 quad op amp IC.  One op amp is utilized.  The resulting output is a clipped sawtooth wave.  Does the fet only switch on and off at certain thresholds or is it continuous output?  Does anyone know a way to use the other op amps to modify the duty cycle/pulse width?  Currently the board produces a sawtooth between 200hz and 8khz with a 100pf cap and 100k ohm  pot.  Click 'My experiments' at the bottom of this page students.umw.edu/~jsera9mu/wfc%20site
to see my progress and schematics.

[Spewing]

The fet is a Silicone AMP. 2 types of silicone is used. The gaet of the fet is between the source and drain, when you put current at its gate then electrons jump the barrier.

Fets Like to be ON or OFF. Fets do not like to be inbetween, "like we're using them." So when you refer to High amp pulses what you mean is you can switch the fet on and pulse high amps, then shut the fet off to repeat.

When you pulse with a frequency like we, you are talking about, The fet never turns all the way on. Therefore when you do this to the fet it acts as a resistor. Anything that resist current gets hot.

If you want to improperly run the fet, "the way all of us has been doing it," then run your signal to the gate and use a 820 ohm and 220 ohm resistor just like dave lawton did in the D.14 PDF. The 2 resistors can be replaced with pots to control the amplitude of the fets output. Its not recommended to pulse high loads when the fet is being abused in resistive mode or acting as a resistor, however adding chokes reduces current flow helping to protect the fet since the part of the circuit with the most resistance takes the heat, heat is then stirred away from the fet allowing it to act as a frequency amplifier.

To better answer your question, look at the d.14 pdf, pin 3 of the timer is the clocking output. 

[Jokker]

Just remember that ...

Collector as collecting very low resistance.
Emitter as emitting  med resistance...

And finaly is base what acts as switch between tease 2.


Apply for example 2 - 5 V to base and resistance between collector and emitter will be low and another way ...


MosFet is just good for switching due PN junction properties.
Gate as base ... source as collector and drain as emitter.


Maybe im wrong but idea should be working. If u will mix emitter and collector is will be nothing noticeable but just not efficient 

[gyulasun]

Maybe im wrong but idea should be working. If u will mix emitter and collector is will be nothing noticeable but just not efficient 

Hi,

I assume you agree on naming your term emitter as the source and your collector as the drain of a MOSFET, right?

Now if you mix up the two, the built-in body diode which is normally reverse biased when the drain gets a positive voltage with respect to the source (in case of an N-channel FET) will immediately conduct and short circuits the drain-source path.  This is not what you want so do not mix up the drain with the source. (Most of the junction FETs (jFET) can work with mixed up drain-source but power MOSFETs cannot.)

@Farlander    here is a link to read and learn some more:

http://hades.mech.northwestern.edu/wiki/index.php/Driving_using_a_single_MOSFET  or

http://en.wikipedia.org/wiki/Power_MOSFET

rgds,  Gyula

[Spewing]

Gate, Drain, Source.

GDS