Dimmable constant current LED driver for single LED - Page 1
Forum section: electronics / projects

author: cowana
author_rank: Frequent Contributor
timestamp: September 04, 2015, 09:19:33 am
content: I have a desk lamp, which consists of a single white LED (rated somewhere around 3W), and a constant current 'plug pack' driver (240v in, output rated at 600mA CC, at somewhere around 3.5v).The existing power supply seems to be built down to a price - the current regulation seems poor, with the light occasionally flickering or changing brightness, so I would like to replace the power supply.I would like to be able to dim the light (probably from a microprocessor) - as the existing power supply is trying to supply a constant 600mA, I would imagine it would be unhappy with PWM switching on the output (and likely it would maintain the *average* current at 600mA - ie no dimming). LED driver modules (240v in, CC out) seem fairly common (although I suspect finding one that works down to such a low voltage could be hard). However, I would imagine that these would exhibit the same issues with PWM dimming, as they're not designed to be used with external switching on the output.Are there any other options for prebuilt single-LED drivers with dimming/PWM inputs? I could roll my own using a driver IC, but that seems overly complex for such a simple job - plus I would like to avoid having to build the 240v stage, so would likely use an external 240v to 12v plug pack, then my circuit would consist of a buck converter to drive the 3.5v LED at 0-600mA. Any suggestions for that buck driver?Thanks for any input!

author: ajb
author_rank: Super Contributor
timestamp: September 04, 2015, 02:17:17 pm
content: Not sure what sort of options you have in the mains-supplied realm, but for a DC-DC solution, check out the Meanwell LDD series. The ones up to 700mA have a control input that can be PWMed, the 1000 and 1500mA versions have analog or PWM inputs. And they're super cheap.

author: LaserSteve
author_rank: Super Contributor
timestamp: September 04, 2015, 02:45:56 pm
content: Take a look at the "Buckpuck" series from Luxdrive. You'll need a DC supply, but I have had very good luck with their 0-10V and potentiometer versions. Only annoyance is an occasional bright flash at turn on with the potentiometer version set to 0.00V /grounded input. But the flash does not exceed the upper I limit. Make sure you get a version which supports single leds, there are many options. I use them for microscopy illumination and strobing in a research environment.Steve

author: DanielS
author_rank: Frequent Contributor
timestamp: September 05, 2015, 06:08:34 pm
content: If you want to dim a constant-current supply, you shunt the unwanted current to divert it away from the load.The nice thing about CC switching supplies is that a reasonably well designed one should be able to safely withstand an output short indefinitely since it causes minimal change in the switcher's losses while reducing output power to wiring losses at the nominal or set output current.

author: Morgoroth
author_rank: Regular Contributor
timestamp: September 05, 2015, 06:26:51 pm
content: A cheap and monolitic solution isSTCS2A, input voltage up to 40V, up to 2A by resistor, so you can choose the desired current you need or replace your actual led for a better one, more efficient or powerfull, PWM controlled, with fault connection pin and enable pin, I used and work perfect.the PCB is done in 1 hour or less.I used an ATTiny 10 to read a potenciometer and control the driver, powered by batteries, the leds are CREE-XML, work just great with small footprint.M