Best mosfet/Transistor for driving a PI coil

Dear Vague,

in the PI-detectors generally  using type: IRF9640 FET, with cooler. If original cooler not available for this tr., please use for cooling a small blended brass or alu plate.

The FET-price is about one USD.

See this link:

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(After visiting this link, just simple click to IRF9640, this bring up own pdf-file. If this IRF not good for You, click to another type and read pdf-s).

Sorry, ?'m beginner in this forum, and *dont* the link-insert symbol between many exotic pictograms.

Brg

Rumcajs


Posted on: March 31, 2011, 03:31:42 AM

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Pardon, You are wanted an N-channel FET. Maybe good: IRF 530.

Rumcajs

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Hey!  You may want to take a look a Silverdogs shop.   He just lives around the corner from ya and offers some kick but kits for more then a decent price.

I bought the Surf PI kit and still waiting to put it together , but a mess of them have been completed and there a good little machine.

If your just a starter, the documentation is here and would be a good learning step for you.

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http://www.thunting.com/smf/index.php/topic,22414.msg158824.html#msg158824

It's still a good learning platform.

Do you have a O-Scope?

The Hammer Head is set up as a development Tool to start with.

You have Control of almost every function the detector can do.

It's quite a bit more complicated to put together, but you can do a pile of things to it learning all functions.

As far as Electronics go, you have :

DC Voltages

DC and AC (Z) resistances

Capacitance

Inductance  (To include, Transformer Principles, Fly Back, EMP Theories)

Timing Trains

Amplifiers

Sample Methods and Processing

Audio Modulation

and More.

And when your done, you have a kick but Metal detector.



 

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		Quote:			Posted by Vague
	Hi I am new to this and I am thinking of building a PI detector. I am looking for some advice on which mosfet is the best for driving the coil. I have not decided on a circuit yet but I want to buy the components so that I can experiment. I would be using a 12v supply with an N channel mosfet able to drive <10A. Anyone got any advice on which mosfet to buy? Thanks

As with most electronics, there are many reasons for choosing one component over another. In this case, since you will be working with audio frequencies or low frequencies, just about any will do for the frequency issue. The next thing you need to know is your control voltage. For 5v to 12v control (that's the gate voltage), there are a range of devices. Next, you need to determine the flyback voltage of your coil circuit to select the rating of your device. Normally, 400v to 600v is typical. That's the peak voltage through the device from source to drain when it is switched on. Bear in mind that with proper design you will never see that much voltage but it could very well be present if a component fails. The source to drain resistance is also important because that affects the rise time of your pulse and the decay time of your pulse. Both factors are important for detecting metals. Too short a decay, you miss gold. Too long a delay and you miss everything.

This is not a design project for the faint of heart or the inexperienced. You are much better off building a design that you are already sure works. As you can tell by my last paragraph, there is a very steep learning curve which will frustrate you rapidly. You have been advised to build the circuit that Silverdog is selling. I concur with that.

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I also think that the best FET IRF9640.

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