Driving five 1 watt LEDs - Page 1
Forum section: electronics / beginners

author: yashrk
author_rank: Frequent Contributor
timestamp: July 18, 2014, 07:30:22 pm
content: Hello Guys,I have four 3.7V batteries to drive five 1 watt LEDs. (Total 5w)I want to build a circuit to drive them at their max luminosity but keeping the circuit cheap as possible and efficient as possible.So certainly I need a circuit which can control the amount of current flowing through the LEDs.I was thinking of using all four batteries in parallel (giving 3.7V ) and controlled by a MOSFET by feeding PWMat gate and changing duty cycle to control the current will it work or it will just make a dimmer circuit.Please provide better circuit for controlling the current and feel free to arrange batteries according to your will for getting whatever voltage required as I will be using them only to power LEDs. (Please do not suggest any circuit using specialize ICs as they are hard to find there).Thank You.

author: gregallenwarner
author_rank: Regular Contributor
timestamp: July 18, 2014, 07:37:37 pm
content: The way I usually go about driving power LED's is with a CAT4101 LED driver IC. It's a linear current regulator, which means it's not the most efficient, and you will need to add some heat-sinking, however, they are dirt simple to use. Current is set by connecting a resistor of a certain value to one of its pins. The datasheet tells you how to do this calculation. They're not as efficient as a switching regulator, however, they're really really cheap. In fact, I just requested some free samples from ON Semiconductor and got a handful of them for free. Here's the link:http://www.onsemi.com/PowerSolutions/product.do?id=CAT4101Edit: I should add: That product page says they're 1A, but that'sup to1A. You can set it lower. It also says PWM. That's not in reference to the current limiting. The current limiting is done linearly. The PWM that they're referring to is the ENABLE pin on this chip, which allows a uC or clock source to perform PWM dimming of the LED, which is a really handy feature. You can also just turn the regulator off using that pin to turn off the LED's.

author: mariush
author_rank: Super Contributor
timestamp: July 18, 2014, 07:56:53 pm
content: A lot of companies ship components to India. There isRS-Components, there isFarnell.First of all, define what LEDs you have. What is the forward voltage?Depending on the color of the LEDs, it will have a different forward voltage.. red leds usually are 1.8v, white and blue are 3-3.2v. That's for one LED die, but high power LEDs can have several dies in parallel or in series inside the actual LED. If the dies are connected in series, the forward voltage is multiplied by the number of dies.For example, your LED could have 4 dies of 0.25w each, all connected in series, in which case the LED will need 4 x 2.5-3.2v ( 10-13v) to work. You gave us too little information.You get the best efficiency with a buck led driver, and that means your batteries should have a voltage higher than the LED forward voltage.I recommend using the batteries in series, as that will reduce the current pulled from each one and discharge them somewhat evenly. 4 x 3.7v will give you about 13-15v, which should be enough to power all those five leds in series using a buck driver.Plenty of led drivers here to pick :http://in.element14.com/led-drivers

author: polishdude20
author_rank: Contributor
timestamp: July 18, 2014, 08:17:42 pm
content: Check out Jullian Illet's youtube channel. He buys lots of cheap LED drivers from Ebay and reviews them.