noob with LED drivers

[NeXuS]

Hi all, this is my first post so please be nice!

i am in the process of building some LED rear lights for my car,

so this means that i am working with a wide range of voltages, (6v to 30v)

I want to use 1w COB bead type LEDs, the very common round types.

I also want to drive the LEDs individually, so i can turn on or off individual LEDs.

as far as i am aware, the only way to do this is to have a driver for each LED, there is no simple way of having a pre regulated and current limited supply that a pool of LEDs can use independently.

I understand that i need a driver, because a resistor gives a fixed resistance, and won't maintain a constant current when the voltage fluctuates as much as it does in a car (is this right?)

so i settled on the PT4115 constant current LED driver. I noticed that ebay sells a lot of these LED drivers for 1w LEDs and it uses this chip as its centre. Reading the datasheet, it says that this chip has a wide input range of about 4v to 30v which sounds perfect for my automotive environment.

so i built a simple driver, only to find that what voltage i put in, i get out the other end. so for example i wire it up to a 12v supply and the output to the LED sees 12v as well. i haven't risked wiring an LED up because i don't want to burn it out. The LED is rated for 2.8v

but then i had a thought. if you wire up an LED to a car battery with a resistor the LED will work and not burn out, but it must mean that the resistor is not only limiting the current, but it must be dropping the voltage too.

so if i wire up the LED, will the PT4115 sense the current draw and automatically adjust the voltage too? and the only reason i am seeing 12v at the moment is because there is no LED wired up?

if this is not the case, does it mean i will also need a regulator for each LED? something that takes 6-30v and drops it down to 2.8v and then pass it through the PT4115 to regulate the current? because that is going to be very complex and take a lot of space.



also i have bought an LED driver from ebay, also based around the PT4115, which (according to the ebay listing) is rated at 12v and will drive a 10w LED. i assumed that i could string 9 of my 1w LEDs together and drive them with this driver. (i will have individual LEDs, but also clusters of LEDs)

but when i wired it all up it didn't work. on the other side of the PT4115 was 12v, which i calculated was no where near enough voltage to drive 9 LEDs (in series) and these 10w LEDs are rated to 30v, so i have no idea how this regulator was ever going to drive a 10w LED with 12v.

Am I doing something wrong, or is my maths sound and i've just been conned by cheap chinese crap again?

any tips or help towards my quest would be greatly appreciated!

Thanks!

 

[Norm]

:welcome:

You won't be able to achieve all of the above and still have a street legal car.

Please see rule 11, which in part states: You agree, through your use of this BB, that you will not post any material which is illegal or which promotes activity that is illegal or could reasonably be foreseen to threaten any person's safety.,

Norm

 

[-Virgil-]

Norm's right. Homemade vehicle lights are not legal, and generally are not safe. All vehicle lighting functions are regulated in detail as to their color, intensity, distribution of light, intensity maintenance with prolonged operation, and other performance aspects as well as physical characteristics (vibration resistance, seal durability against moisture and dirt entry, resistance of materials to UV and abrasion, etc). This can't be done in a guesswork fashion, and it can't be tested using home tools. Please save the home builds for flashlights and other non-regulated, non-safety-crucial devices.

 

[NeXuS]

thanks for the replies guys,

actually i am modifying some existing LED lights which have been badly designed (they just use resistors) but they are perfectly legal lights, i just want to improve them so they will last longer.

I also work with LED car lights at work, but they are a lot more simple because they run a string of 18 lights, meaning its just a single boost regulator and not a buck/boost regulator and not individual LEDs,


but regardless of my plans for these lights, can someone answer some of my questions about the drivers and how they should work?

thanks for your help!

 

[-Virgil-]

Sorry, no. The lighting modifications/products you're asking about or recommending are illegal and/or unsafe. Rule 11 of this board prohibits advocating illegal or dangerous activity.