Relay and MOSFET help - Electronic Circuits Projects Diagrams Free

madmikejt12 · 4th November 2006, 02:39 PM

hi, i have designed a circuit on chrocodile technology and everything works apart from when i press one of the 'set' switches, the MOSFET blows up and it says something about the drain voltage

any ideas?

same thing happens when using a transistor
here is what i have done:
http://i14.photobucket.com/albums/a3.../untitled5.jpg

it is the MOSFET on the end of the 1st part of the circuit (under the relay coil) that blows up

Dr.EM · 4th November 2006, 03:07 PM

6v should be fine, so i'm assuming its the lack of a protection diode on the relay coil? When the relay turns off, the inductance of the coil creates a brief high voltage spike which can damage both transistors and MOSFET's. Look here to see an example of how to use the protection diode:

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

Its rather an unusual symbol for a MOSFET too? Not the one i'm familiar with.

madmikejt12 · 4th November 2006, 03:15 PM

of course.. that did the trick

Thanks alot

http://www.physorg.com/newman/gfx/news/mosfet.jpg is that something like the symbol you are used to?

Dr.EM · 4th November 2006, 03:33 PM

Yep, thats the one I use; not always with the circle, but broken lines at least.

madmikejt12 · 4th November 2006, 03:38 PM

yeh...

Thanks for your help anyway.

all i need now is:
Front door opend--->6 second time delay---> if code not entered alarm goes off, if it is entered, alarm is de activated

put them both together, and then my alarm is complete

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4th November 2006, 02:39 PM	(permalink)
madmikejt12	Relay and MOSFET help hi, i have designed a circuit on chrocodile technology and everything works apart from when i press one of the 'set' switches, the MOSFET blows up and it says something about the drain voltage any ideas? same thing happens when using a transistor here is what i have done: http://i14.photobucket.com/albums/a3.../untitled5.jpg it is the MOSFET on the end of the 1st part of the circuit (under the relay coil) that blows up

4th November 2006, 03:07 PM	(permalink)
Dr.EM	6v should be fine, so i'm assuming its the lack of a protection diode on the relay coil? When the relay turns off, the inductance of the coil creates a brief high voltage spike which can damage both transistors and MOSFET's. Look here to see an example of how to use the protection diode: http://www.winpicprog.co.uk/pic_tutorial_extras.htm Its rather an unusual symbol for a MOSFET too? Not the one i'm familiar with. __________________ Angry!? I'm absolutely electrolytic! Will have to make do with myspace now I guess...

4th November 2006, 03:15 PM	(permalink)
madmikejt12	of course.. that did the trick Thanks alot http://www.physorg.com/newman/gfx/news/mosfet.jpg is that something like the symbol you are used to?

4th November 2006, 03:33 PM	(permalink)
Dr.EM	Yep, thats the one I use; not always with the circle, but broken lines at least. __________________ Angry!? I'm absolutely electrolytic! Will have to make do with myspace now I guess...

4th November 2006, 03:38 PM	(permalink)
madmikejt12	yeh... Thanks for your help anyway. all i need now is: Front door opend--->6 second time delay---> if code not entered alarm goes off, if it is entered, alarm is de activated put them both together, and then my alarm is complete