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Forum Index : Electronics : Opening a MOSFET with a MOSTFET - how?

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macm
Newbie

Joined: 26/03/2008
Location: Sweden
Posts: 4

Posted: 11:31pm 13 Apr 2008

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Hi all.
Thanks for the help on the current-sensing for the piclog. I ordered a current sensor sample from Allegro and that works perfect.
Now my problem is that I want the Piclog to open a paralel series of MOSFETS. The problem seems to be that the MOSET on the Piclog-board opens the negative and that it takes a positive to open the the paralel series of stronger MOSFETS.
How do I use the negative(-) to create a posetive (+)??

(I have 12 MOSFETs in paralel that is to open 800w/13v to a dumpload)

Regard from Gotland - sweden
Mikkel

Robb
Senior Member

Joined: 01/08/2007
Location: Australia
Posts: 221

Posted: 04:33am 17 Apr 2008

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A simple in inverter (inverter as in logic state inverter not power inverter). Something like...

A rather basic drawing but ....

macm
Newbie

Joined: 26/03/2008
Location: Sweden
Posts: 4

Posted: 08:26am 17 Apr 2008

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Okey - logic state inverter. I tried the wiki and came up with: Inverter (logic gate)
(Im so in over my head :-)
http://en.wikipedia.org/wiki/Inverter_(logic_gate)
Is this the thing?

Regards MikkelEdited by macm 2008-04-19

Robb
Senior Member

Joined: 01/08/2007
Location: Australia
Posts: 221

Posted: 06:09am 22 Apr 2008

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Thats the general idea you want as far as I can tell from your first post.

Basicly:
logic high in ---> logic low out.
Logic low in ----> logic high out.

The above circuit does that.
Do you understand transistor basics? If not that would be a good place to start.

You could use an actual off the shelf logic gate chip but thats probably over kill for what you want.

GWatPE

Senior Member

Joined: 01/09/2006
Location: Australia
Posts: 2127

Posted: 07:00am 22 Apr 2008

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Hi Mikkel,

You have a piclog cct and you presumably have downloaded the code to the picaxe. You would have to modify the code to use a hall effect current sensor.

All you probably need to do is mod the code. I think it is output 2 that is used. Substitute a low for a high and vice versa in the code. Check that it is output 2.

No soldering or understanding transistors may be needed. .. Gordon.

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