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kkdelabaca
Joined: 18 Apr 2003
Posts: 106
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 07 Feb 2007 12:15 Current source for POWER LEDS |
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Hello,
I need control the current of the 4 power white LEDS.
Somebody know any driver to regulate de current from 100mA to 300mA in each LED?
Regards!
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servicemann
Joined: 20 Jan 2006
Posts: 189
Helped: 13
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07 Feb 2007 12:37 Re: Current source for POWER LEDS |
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Somebody know any driver to regulate de current from 100mA to 300mA in each LED? |
What do you mean with 100mA to 300mA?
I suppose the diodes are in serial.
Look for "current driver" in some IC manufacturer.
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kkdelabaca
Joined: 18 Apr 2003
Posts: 106
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07 Feb 2007 14:34 Re: Current source for POWER LEDS |
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I need regulate the light of the diode and therefore need change the current from 100mA (low light) to 300mA (full light).
Yes, I prefeer the leds in serie.
Regards!
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leptronik
Joined: 08 Jan 2003
Posts: 4
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07 Feb 2007 16:52 Re: Current source for POWER LEDS |
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hi,
the lm317 can be use as current source, if yo use correct resistor value can adjust it to your requierement.
this is an idea.
A+
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Koson
Joined: 04 Oct 2006
Posts: 43
Helped: 6
Location: Bangkok, Thailand.
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07 Feb 2007 17:55 Current source for POWER LEDS |
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You can use SG3524 switching mode power supply controller for low loss, but it's more complex cct.
More complex circuit --> Less power loss = save our planet.
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szekit
Joined: 25 May 2006
Posts: 89
Helped: 5
Location: Hong Kong
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09 Feb 2007 2:07 Current source for POWER LEDS |
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i guess each power led has certain Vforward? it would require quite a high voltage to switch on all the leds in series.
u can adjust the brightness by controlling the current (analog) or through PWM (digital).
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Willt
Joined: 17 Mar 2006
Posts: 78
Location: Hong Kong
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09 Feb 2007 2:43 Re: Current source for POWER LEDS |
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MAX1553 - Maxim
LTC3422 - Linear
For your reference ~
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Google
AdSense
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09 Feb 2007 2:43 Ads |
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ashad
Joined: 28 Mar 2006
Posts: 307
Helped: 9
Location: Singapore
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12 Feb 2007 7:31 Re: Current source for POWER LEDS |
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very cheap solution
use ULN2803
ULN2003/7 i forgot
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JohnJ
Joined: 02 Nov 2005
Posts: 55
Helped: 2
Location: St. Petersburg, Florida
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12 Feb 2007 18:16 Re: Current source for POWER LEDS |
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Most LED dimming circuits are PWM. It is difficult to match brightness through the range with DC current.
For those interested in saving energy; an LED is more efficient at higher currents, therefore pulsing using 5x the current for 20% of the time puts out more light than the equivelent DC power.
We just finished designing and building an LED HDTV using only 3 LEDs, one for each color in a 52" TV. Even using the inhearent PWM of a TV (i.e. the frame rate), the output of each LED still had to be linearized over it's range by adjusting it's pulse width. (That is in addition to the obvious need to balance each color.)
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felix1200
Joined: 01 Jan 1970
Posts: 41
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12 Feb 2007 18:32 Re: Current source for POWER LEDS |
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What is your power supply ?
This is an important question.
Power LEDs have a forward voltage between 2.5V and 4.5V (see datasheet). This means
that they need a supply voltage about 10V..18V in series. So your
supply voltage for the LEDs must be approx. 20V (worst case).
To keep the power dissipation small use a switched mode power supply (SMPS).
Dependent on your Supply Voltage you can use a stepup, stepdown or a combination
of both SMPS. Use it as a current regulator.
See for example on www.maxim-ic.com an appliction note for MAX5035.
To modulate the light density you can source an additional current into the
feedback input of the regulator. Some LEDs change the color temperature when
the current through the LED is changed. This is mostly not important.
A different solution is to make a smps as a voltage source and modulate the light
density via PWM. The LEDs are supplied with 300mA. The advantage is that the color temperature of the LEDs is constant. Use a LOW RDSON-FET. Plese no ULN...
it can burn away (600mW power dissipation can be too much for this package)
felix1200
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