Maker Pro
Maker Pro

Luxeon star driver

M

Mike

Jan 1, 1970
0
Is there a diagram out there to drive a Luxeon III star from 12V without
having to use a huge limiting resistor?

--
THE BOULDER PLEDGE
"Under no circumstances will I ever purchase anything offered to me as the
result of an unsolicited e-mail message. Nor will I forward chainletters,
petitions, mass mailings, or virus warnings to large numbers of others. This
is my contribution to the survival of the online community."
 
E

ehsjr

Jan 1, 1970
0
Mike said:
Is there a diagram out there to drive a Luxeon III star from 12V without
having to use a huge limiting resistor?
------
+12 ----| 7805 |---[2R]--- Vout to Luxeon, 650 mA
------
|
Gnd --------+

Figuring Vf at 3.7 volts, 2 ohms will limit current to
650 mA, so a 2 watt resistor will do. The 7805 can
go up to 1 amp, and needs a heat sink. It will dissipate
up to ~7 watts. If you want to go "full bore" (>1A), use
a different circuit:

------- 2W
+12 ----| LM317 |---+---[1R]--- Vout to Luxeon
------- |
| [240R]1/2W
| |
+-------+---[2.2K]------+
| 1/2W |
[810R] 1/2W [POT] 5K
| 1/2W |
Gnd --------+-----------[120R]------+

The above will allow you to vary the current to the Luxeon
from about 670 mA to 1.34 amps.

You could use a 2 watt one ohm limiting resistor, but it will
dissipate about 1.4 watts, so a little higher wattage gives a
wider margin and is desireable. The other resistors are 1/2 watt.
The LM317 will need to dissipate ~ 10 watts, so a heat sink
is needed.

Ed
 
R

René

Jan 1, 1970
0
Is there a diagram out there to drive a Luxeon III star from 12V without
having to use a huge limiting resistor?

I would get a $0.40 MC34063, a a well chosen inductor, and make a low
dissipation current source. ~600 mA without external boost fet /
transistor is achievable.

Beats huge heatsinks etc. Including the ~ 50 uH inductor it would be
cheaper too I guess. My 0.02
 
M

martin griffith

Jan 1, 1970
0
Top