2 questions, 1)Any suggestions off the top of your head of a MOSFET I can use? 2) How would one go about finding the correct part w/o having to go through a million datasheets?

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Thank you,
Dan

Ive got a head full of ideas and a wallet full of cobwebs

 

I buy some of my stuff from ebay sellers. In this case I would simply search for logic mosfet. You'll notice that logic level mosfets are more expensive than the others, but they save the hassle of boosting the drive voltage.

You need to decide what current you need, and how many parts. Also surface mount, or not?

 

You don't need a logic level MOSFET.

As this is a p-channel MOSFET so you need a MOSFET driver to convert the 0-5V pulses to 0-9V pulses.

If you just used a logic level p-channel MOSFET then it would never turn of, it will stay on when the PIC's output goes high.

Also, what power supply are you using?

If it's just a 9V battery, the voltage will quickly drop to 7.5V and it might not work.

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I am using a regular old 9v batt

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Thank you,
Dan

Ive got a head full of ideas and a wallet full of cobwebs

 

How much current are you planning to draw?

If it's over 100mA or so then I strongly advise using a larger battery like six AA cells.

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Im only drawing about 10mA. Unfortunately I dont have the space for AA cells.I do plan on using Nimh Button cells though. I was going to use 7 connected in series giving me 10.1v @ full charge, Im using it in a different variation of this circuit, where Im using the PicAxe as a power switch for a 555.

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Thank you,
Dan

Ive got a head full of ideas and a wallet full of cobwebs

 

If it's just 10mA then why not just use a PNP transistor?

The circuit for driving one from a PIC is shown below.

http://www.winpicprog.co.uk/pic_tutorial_extras.htm

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Like I said I am just playing around w/ this. Seeing what I can, and cant do with different components, and configurations. Right now Im using an N-chan(2n7000) to pulse the (-) side of the circuit, but would rather pulse the (+) side. I was going to use an NPN, PNP similar to the schematic you posted, but Ive been playing with these MOSFETS lately and was curious if I could get the same result.

__________________
Thank you,
Dan

Ive got a head full of ideas and a wallet full of cobwebs

 

You could replace T2 with a MOSFET and remove R3 but R2 will form an RC circuit with the MOSFET's gate capacitance which will slow the off time too much for 30kHz operation.

If you want to drive your MOSFET at high speed, you need a MOSFET driver. You can use a special IC (recommended) or build your own from a few transistors (see attachment). In this case you only want to pulse the load at 10mA so it's not worth going to all the trouble, even more so considering the driver uses nearly as much current.

Attached Images

MOSFET Driver.GIF (7.1 KB, 4 views)

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I was playing around last night using an N-chan (2N7000) and a P-chan(IRFU9020), set up similar to the first schematic you posted, and had very good results. Using my 10v batt pack, I got an output of 9.82v @ 30.2KHz w/ a 6.28mA draw from the batt. The batt only dropped <1v after a full run(10 min pulse 4x, 20 min pause between pulses, then complete shut down of the circuit) then Im using the same setup(N,P-chan) for the power hold on the PIC. Ill draw the schematic later.

__________________
Thank you,
Dan

Ive got a head full of ideas and a wallet full of cobwebs