Led Driver from 10 to 30vdc - Page 1
Forum section: electronics / projects

author: rem4
author_rank: Newbie
timestamp: February 01, 2021, 08:11:38 am
content: Hello,I have designed an electronic schematic to drive led from 10vdc to 30vdc.Attached my design.It work with AL5809-20P1-7 driver.When I apply a supply voltage about 15VDC it work fine, but when I apply a voltage about 24vdc the IC is very hot !I think there is a better way to drive these 10 led (20mA @ 3,2v) without an hot pcb.Do you have any idea to improve this schematic ?Thanks

author: Zero999
author_rank: Super Contributor
timestamp: February 01, 2021, 01:28:45 pm
content: What does you mean by very hot? The data sheet says it can work up to 125°C.If you want to reduce the temperature, you have three options:1) Better heatsinking.2) Reduce the power dissipation in the IC, by using a lower current, or reducing the votlage drop by connecting more LEDs in series.3) Use a switched mode power supply.

author: rem4
author_rank: Newbie
timestamp: February 01, 2021, 01:58:43 pm
content: Thanks for your answerThe maximum allowed temperature for this design is 65°c.I have tested better heatsinking with double sided pcb and plated through holes but it's not enough.Do you know a component for the switched mode power supply ?Thank you

author: MarkF
author_rank: Super Contributor
timestamp: February 01, 2021, 02:22:26 pm
content: The power dissipation of each AL5809 is the current (i.e. 20mA) * voltage drop across it.As you increase the voltage, the voltage across each LED remains the same and the additional drop is across the AL5809.One way to reduce the voltage drop (hence the power dissipated) of each AL5809 is to increase the number of LEDs in series with each AL5809. It looks like the AL5809 requires a minimum voltage across it of 2.5V. Depending on the LEDs that you're using, you may be able to have just two AL5809 branches with 5 LEDs in each with the 24V power supply. For LEDs with a 3V forward voltage and 5 in each branch the AL5809 will only need to drop 24V - (3V * 5) = 9V. The power dissipation of each AL5809 then is 20mA * 9V = 180mW.

author: rem4
author_rank: Newbie
timestamp: February 01, 2021, 02:30:15 pm
content: Thanks.My leds are 3,2v @ 20mA.The problem is the input voltage is from 10v minimum to 30v maximum.This is why I place 2 leds in series (3,2v * 2) + 2,5V from AL5809 = 8,9VMy problem is about the variation of voltage of the input.I think AL5809 are not the best way to drive for this configuration.

author: wraper
author_rank: Unknown
timestamp: February 01, 2021, 02:40:22 pm
content: If you want low heat over wide input voltage range, use switching driver. IMHO the most appropriate would be boost converter and connecting all 15 LEDs in series.

author: Zero999
author_rank: Super Contributor
timestamp: February 01, 2021, 03:47:09 pm
content: You could use an LED driver kit/module, similar to the Velleman K8071, or copy the schematic off the data sheet.https://www.velleman.eu/products/view/?id=366712&country=us&lang=enhttps://www.velleman.eu/downloads/0/infosheets/k8071_uk.pdfUnfortunately it's designed for 350mA, or 700mA, which would destroy your LEDs. You need to modify it for 100mA, by changing R6 to 3R6 (leave R7 unfitted) and connect the LEDs in five parallel strings of two in series. If you don't need it to run off AC, just DC, skip the bridge rectifier, for better efficiency and performance, at lower voltages, but don't connect it backwards!https://www.velleman.eu/downloads/0/illustrated/illustrated_assembly_manual_k8071_rev1.pdf

author: thedrummer2016
author_rank: Contributor
timestamp: February 01, 2021, 04:00:09 pm
content: My opinion would be to drive this with a switching power supply as some others have stated. There are many options for drivers but I have used some very low cost and fairly efficient Maxim buck/boost converters for battery powered applications where the voltage swings over a fairly large range.