I can't seem to find a cheap single white LED driver - Page 1
Forum section: electronics / general

author: ivan747
author_rank: Super Contributor
timestamp: June 30, 2012, 10:36:39 pm
content: I've been looking on Digi-Key and I am having trouble finding a white LED driver to connect directly to a single li-ion cell and that can handle a single (actually, two parallel) LED. I am looking for something that costs less than $1 for 100 units.The closest I've found is this:http://www.digikey.com/product-detail/en/MIC4801YM/576-3856-5-ND/2621443And it is on the expensive side.Perhaps I should look for some sort of LDO constant current source?The LED voltage is 2.8V-3V.Additional info:There is also a 3.3V rail that comes from a Buck-Boost converter.I really like this chip, but there's nowhere to get the required voltage from (3.6V):http://www.diodes.com/datasheets/AL5802.pdf

author: tom66
author_rank: Super Contributor
timestamp: June 30, 2012, 11:17:05 pm
content: http://www.ti.com/product/LM2796162 cents 1ku.

author: IanB
author_rank: Super Contributor
timestamp: June 30, 2012, 11:23:50 pm
content: You have not given your specifications completely enough. What kind of LED is it, and what is the required drive current? What is the application? Are you concerned about efficiency? This may determine whether you want a linear regulator or a switching regulator (although with a single Li-ion cell it may not make much difference).When asking a question, always give as much information you can, starting with what you are trying to build, how you have approached the design so far, and then give the point where you have hit a snag.

author: T4P
author_rank: Super Contributor
timestamp: July 01, 2012, 02:23:31 am
content: You haven't given the wattage of the LED,if it's a 3W LED about there or about you can use the 2.7V-4.2V 1000mA current regulator AMC7135 or just 7135 boards from dealextreme that was intended for a flashlight

author: ivan747
author_rank: Super Contributor
timestamp: July 01, 2012, 03:15:50 am
content: I am driving an LCD display backlight. There's not much info on the datasheet about the LED. This is all I have:http://www.newhavendisplay.com/specs/NHD-C0220BiZ-FSW-FBW-3V3M.pdfIt's the same LCD Dave uses for the portable power supply (not the USB one) but with a white backlight. If you noticed, it uses 2 LEDs in parallel.I am mainly looking for linear ones, although I have a neat idea:My design uses a board as a front panel, similar to the µCurrent, except the circuitry is on a different board. There are buttons that need light. (they are pushbuttons, so the buttons themselves don't need light, the labels do).Since it is much easier to find LED drivers that drive 2+ LEDs in series, I can use some LEDs to light up the labels on the front panel and have them in series with the backlight. I just have to make sure that both the display and the discrete LEDs emit an adequate amount of light.I ordered the display already and I have a feeling that the LED will be too bright at full current (30mA).

author: IanB
author_rank: Super Contributor
timestamp: July 01, 2012, 06:30:13 am
content: Since your supply voltage from the Li-ion cell is going to be greater than or equal to about 3.3 V and the LED only requires about 30 mA at 2.8-3.0 V it looks like a simple linear LDO constant current source would do fine.To put two LEDs in series you will need a boost converter and this is more complex. It doesn't necessarily save you anything to do that.

author: T4P
author_rank: Super Contributor
timestamp: July 01, 2012, 06:36:14 am
content: A current regulator would fit the bill*edit: or a ldo like HT7130

author: ivan747
author_rank: Super Contributor
timestamp: July 01, 2012, 12:29:49 pm
content: Quote from: DaveXRQ on July 01, 2012, 06:36:14 amThey have been obsolete for 10 years, apparently. The replacement is the HT7130-1. Let's check that out.Edit: this is not a current regulator

author: ivan747
author_rank: Super Contributor
timestamp: July 01, 2012, 01:00:38 pm
content: Quote from: IanB on July 01, 2012, 06:30:13 amI found a very cheap 2+ LED driver and I have a complete solution for $0.70 (100 of):One chiphttp://www.digikey.com/product-detail/en/AP5724WG-7/AP5724WG-7DICT-ND/2182551The coil:http://www.digikey.com/product-detail/en/MLZ2012N100L/445-6762-1-ND/2523583Current sense resistor:http://www.digikey.com/product-detail/en/ERJ-6GEYJ4R7V/P4.7ATR-ND/282170Capacitors (x2):http://www.digikey.com/product-detail/en/C1608Y5V1A105Z/445-1328-2-ND/513841Diode:http://www.digikey.com/product-detail/en/BAT54/BAT54FSCT-ND/458928The only way to beat this is to find a linear device that can handle all the LEDs in parallel and I've heard it's not a good idea to parallel LEDs with different forward voltages. So I would need a two chips to drive the display and the keypad, one each. That means I need them to be $0.35. I searched on Digi-Key and found nothing.

author: T4P
author_rank: Super Contributor
timestamp: July 01, 2012, 02:59:11 pm
content: Quote from: ivan747 on July 01, 2012, 12:29:49 pmOR a ldo. keeping it limited at 30mA is good anyway