How to drive lLEDs efficiently and cheap?

[MikePL]

Hello

I've been playing with LEDs since 1998 but I've always used them with fairly stable and predictable power sources like batteries. I've always needed resistors only.

Now two things have changed. I will play a bit with high power LEDs and will use them in a car. So I have a high power light source and a very unstable power source (spikes, voltage fluctuations 12-14V).

How do I drive a single 3W 700mA LED from a car's power source. A resistor seems to dissipate lots of heat (waste power), the LM317 seems to be totally useless, PWM drivers have always seemed expensive to me (5-10$ is like the price of a LED, so way too much).

Is there a solution to drive a LED, not waste 50% of consumed power and not pay much for it.

 

[ktronik]

Hello

I've been playing with LEDs since 1998 but I've always used them with fairly stable and predictable power sources like batteries. I've always needed resistors only.

Now two things have changed. I will play a bit with high power LEDs and will use them in a car. So I have a high power light source and a very unstable power source (spikes, voltage fluctuations 12-14V).

How do I drive a single 3W 700mA LED from a car's power source. A resistor seems to dissipate lots of heat (waste power), the LM317 seems to be totally useless, PWM drivers have always seemed expensive to me (5-10$ is like the price of a LED, so way too much).

Is there a solution to drive a LED, not waste 50% of consumed power and not pay much for it.

Hi I love modding my car with LEDs...& I can see where you are coming from...

as LED are so cheap & its in a little car... I just series up 4 LEDs...

so 4 / 8mm 1/2w white LEDs (on the door circuit) & 4 / 5mm 1/2w LEDs for trunk... I just clicked out the plastic 'festoon' fitting... drilled 4 holes & wired it back up...if one burns up one day...well I will replace the $1 part...

My SLA car battery should stop charging @ 13.8v... but could go as high as 14.4...
but when I use the boot (trunk) LEDs & Door LEDs the car is normaly off...

I use 8mm & 5mm LEDs as 4 HP stars would be a bit blinding in the cabin...+ they are much easier to fit & replace...no heatsink, driver or optic / reflector...
4 is the magic number to save money...in this case...

BTW still going strong with NO burn outs...

hey you did say cheap...

have fun... I did..

best

Ktronik

 

[Oznog]

You need a "buck" power supply. You can design one around the HV9910 or ZXLD1360 but that requires some skill. There are some pre-made buck converters out there though.

 

[MikePL]

Thanks for the reply.
Can you throw some diagrams please? I am completely new when it comes to drivers. And are you sure they can withstand 3W of power?