Try to use a power MOSFET and PWM circuit, instead.
This is one examp=
le for driving normal tungsten lamps:

http://www.uslink.net/~cybercir/=
cir13.htm

This isn't PIC related, however may be a starting point. =0D
=

Two notes:

1) Halogen lamps are a bit differents from normal lamps, =
search related notes on the web.
2) If you want to drive a MOSFET with a=
 low voltage, use LOGIC LEVEL gate types.
Other MOSFETs  needs a higher =
voltage to drive the gate (implement a "doubler voltage" circuit), otherv=
ise you will not be able to drive full power from the MOSFET.

regard=
s
MarcoG






---------- Initial Header -----------

From    =
  : "pic microcontroller discussion list" PICLIST@MITVMA.MIT.EDU
To     =
     : PICLIST@MITVMA.MIT.EDU
Cc          :
Date      : Fri, 5 Dec 200=
3 03:34:11 -0800
Subject : [EE]: 12 V light dimmer

> What is the best=
 way to control the dimming of a 12V bulb?  (I have a 12VDC
> halogen b=
ulb rated at 20W)
>
> I saw circuits on the web using a digital pot to=
 control a LM317 (variable
> voltage regulator).
> I also saw circuits=
 on the web using PWM to control the bulb via a transistor.
>
> I trie=
d the second method...using PWM from my microcontroller to control a
> =
MJE3055T.  12 V supply is connected to one lead of the bulb, the other le=
ad
> of the bulb is connected to the collector.  the drain is connected=
 to GND.
>
> The transistor got _really_ hot and the bulb was hardly l=
it...it just
> glowed a bit.  Do I just need a transistor with a higher=
 amp rating?
> Here are the specs for it...
> VCEO Collector-Emitter Vo=
ltage (IB =3D 0) 60 V
> VCBO Collector-Base Voltage (IE =3D 0) 70 V
> V=
EBO Emitter-Base Voltage (IC =3D 0) 5 V
> IC Collector Current 10 A
> I=
B Base Current 6 A
> Ptot Total Power Dissipation at Tcase =A3 25 oC   7=
5 W
>
> It seems like it should be fine.  60V and 10A.  What am I doin=
g wrong such
> that the transistor is heating up so much?
>
>
> Or=
 should I just try the LM317 approach?
>
> The least parts the better.=
..it seems like the transistor approach would be
> best.  Can someone a=
 circuit for this and also recommend the transistor to use?
>
> Thanks=
!
>
> James Tu
> james@2-bit-toys.com
>
> --
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.com hint: The PICList is archived three different
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ww.piclist.com/#archives for details.
>
>
>

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