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I want to build a 90% efficient LED driver circuit with current range from 25mAmps to 35mAmps with the source voltage of 7.4 volts. How can I make it using my Arduino board. Please help.
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I assume you want a constant current output from a circuit, and that current decided upon by the Arduino?

Basically you want to make yourself a switching power supply, but have it monitor the voltage drop across a very small resistor instead of the output voltage.

You want to have something to switch your input voltage driven by PWM (a P-channel MOSFET is normal for that), and you then monitor the current flowing through a small resistor after the MOSFET using the Arduino's ADC - I'd also recommend some kind of high side current sensing amplifier as the voltage difference will be pretty small and offset by more than the Arduino can cope with (yes you could divide it down with a resistor network, but that would then reduce your sensitivity too).  Then, using that ADC reading you can adjust the PWM duty cycle to set the right current output.

The fun part is getting the algorithm right so that you get to the right output current as fast as possible so as to not blow your LEDs up with over current.
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I want to build a 90% efficient LED driver circuit with current range from 25mAmps to 35mAmps with the source voltage of 7.4 volts. How can I make it using my Arduino board. Please help.

How many LEDs? what is voltage of LED?  7.4 volts is power source/battery voltage?
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I want to build a 90% efficient LED driver circuit with current range from 25mAmps to 35mAmps with the source voltage of 7.4 volts. How can I make it using my Arduino board. Please help.

How many LEDs? what is voltage of LED?  7.4 volts is power source/battery voltage?
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How many LEDs? what is voltage of LED?  7.4 volts is power source/battery voltage?

1.) 24 to 32 LED's.
2.) LED load is of 3 to 3.2 volt.
3.) 7.4 is the source voltage which is charging a 3.7 volt lithium ion battery i.e LED's wil be powered by the lithium         
     ion battery.
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What you need is "WLED Driver IC for Notebook Display".

Sample IC, pt4112 for 5-25V system;-

Applications:

Notebook LCD display backlight
General middle-sized LCD backlight

Specification:

V-in: 5-25V
I-LED: 25mA
Number of LEDs: 60(6x10)
Efficient: >85%
Support: independent Enable(on/off) as well as PWM.




Sample IC, PT4110 for 2.7-5.5V system.

Specification:

V-in: 2.7-5.5V
I-LED: 80mA
Number of LEDs: 32(4x8, 20 mA)
Efficient: 85%
Support: Enable(on/off) and  PWM.

P.S. Enable and  PWM are logic level, it is friendly with Arduino.  Some Information of above is combined with English doc and my translated form Chinese doc, so take it with salt. smiley-razz

PT4110's diagram is here;-

http://arduino.cc/forum/index.php/topic,164487.msg1229672.html#msg1229672
« Last Edit: May 05, 2013, 11:40:16 am by sonnyyu » Logged

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