Thank you all who answered to my siren question. Now I got it and hope
it will work :)

Lucian

-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU] On Behalf Of Andrew Kilpatrick
Sent: 17 aprilie 2004 20:16
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [EE:]Driving a siren]

I've made high current drive for 12V halogen lamps up to 100W with
an IRF530 MOSFET. You will find that you need a voltage converter
between the PIC and the MOSFET. The way I did it was with a 2N2222A
transistor. This is wired something like this:


                          +12V          +12V
                          |              |
                          |              -------- LOAD
                          <              -------- LOAD
                          >  10K         |
                          <              | d
                          |___________|--
                1K        | c      g  |--   IRF530
PIC PIN ------/\/\/\----|/               | s
                     b  |\  2N2222       |
                          | e            |
                          |              |
                         GND            GND


This seemed to work very well. The trick is that the MOSFET must
have its gate switch between fully on (+12V) and fully off (0V)
otherwise it will get very hot.


Andrew



On Sat, Apr 17, 2004 at 07:31:31PM +0300, Lucian wrote:
> Thank you for your answers. I think I found an appropriate solution to
> my problem: an IRF630, which is rated 200V, 9A and pulsed current 36A
so
> I think it's ok for a siren. No I have to manage to find a circuit to
> control it from a PIC pin, because I guess it's not correct to drive
the
> MOSFET directly.
> Am I right ? What protection do I have to add ? The FET already has in
> it's internal structure a diode, so I could only put a resistor in
> series with the pic pin ?
>
> Lucian
>
> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU] On Behalf Of Herbert Graf
> Sent: 17 aprilie 2004 18:41
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [EE:]Driving a siren
>
> > Dear Piclisters,
> >
> > I have yet another question for you. I am still a newbie in
> electronics
> > and PIC's and I feel a little bit shamed that I only come to ask
> > questions on this list and rarely know how to answer to other
> questions,
> > but hope that someday I will be able to be more active here.
>
>         Please, do NOT feel ashamed. EVERYONE here was, at one time, a
> "newbie",
> and did what you do (it's called lurking), in fact many PICLIST
members
> still mostly lurk, and there is NOTHING wrong with that, it's why the
> list
> is here IMHO.
>
> > My questions is: I want to drive a siren from a microcontroller pin.
> The
> > siren is an alarm one, and consumes 12V and 3A at maximum. Which
would
> > be the best way to control it (on/off) ? A power MOSFET, a triac
> maybe,
> > a relay ?
> > Thank you for your answers.
>
>         Well the "best" way depends on you and your situation. IMHO
the
> EASIEST way
> is a relay, a simple jelly bean transistor (say a 2N2222 or 2N2904)
> driving
> a relay. The reason I say it's "easiest" is it completely electrically
> isolates you from a devices that may do very ugly things on it's power
> lines
> (sirens can be very inductive causing huge power spikes on the lines)
>
>         The relay solution however isn't the most elegant, uses more
> space then it
> has to and wastes power. The most efficient way would be a MOSFET, use
a
> logic level MOSFET that can handle at least 5A (I'd say get one that
> does
> 10A, the siren is speced for 3A but I'm willing to bet it's surge
> current is
> higher). Check out the company International Rectifier for good parts,
> their
> IRFZ line should be what your looking for, if memory serves.
>
>         TTYL
>
> ----------------------------------
> Herbert's PIC Stuff:
> http://repatch.dyndns.org:8383/pic_stuff/
>
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