20W LED driver

[joco000]

Hello,

I am in time rush and need to design 20w led driver circuit.
input: 12V
Output: 1 LED, 20W, 1.5A/13V

circuit should have PWM dimming input
Driver IC should Farnell have on stock

If anyone have designed it before, would you be so kind and share with me.

Thanks,
joe

 

[alec_t]

That's not as straightforward as it sounds and will involve more than a driver IC.
Firstly, you will need a DC-to-DC converter to raise the voltage above 13V. Secondly you will need a PWM controller.
Thirdly you will need some way of limiting current through the LED, ideally without wasting too much power.
Why the rush?

 

[joco000]

we are going to dive end of next week.
pwm will make with uC.
I know that I need boost-buck converter, if I find some aplication note with such demands it would be great
I am thinking first to make dc/dc 12 to 24v, with this maybe it would be easier to find AN.

regards

 

[ronsimpson]

"input: 12V" often people say 12V when they mean automotive 12V which is not 12V but could be 10V to 12V with the engine off or 14V (maybe 14.5) when running. Under some conditions may get to 20-30V. Do you really mean "input: 12V" or 10-15V auto?

"Output: 1 LED, 20W, 1.5A/13V" I have seen "LEDs" that are built for automotive that include a resistor. We need the part number. A LED's voltage is not accurate! The data sheet may say typically 12V with a max of 14V and a min of (?). So we need to build a 1.5A constant current PWM that works with LED voltages of 10 to 14 volts.

Because the power supply might be larger or smaller than the LED voltage things are slightly more complicated. A SEPIC PWM works well then the input and output are about the same. The application note from TI shows a 10-18V input, LED is 19V but I believe it will work fine at 13V, 2.5A which needs to be changed to 1.5A by changing R8. You don't need the op-amp.

The On Semi application is a good read. 1A max.

The Linear data sheet is OK.

I do this for a living. I can help a little but not much. Many time I have used Zetex parts. I would probably use a single inductor SEPIC/boost PWM.

 

[bountyhunter]

+1 On Ron's input: you need to actually define the specifications before you start to design anything. Don't let anybody rush it..... as I learned in my 30 years in electronics design (but no manager ever learned):

Never enough time to do it right......

Always enough time to do it over.

The TI circuit looks like a good fit. Build it up, test it and tweak it until it does what you need, then you are done.

 

[ronsimpson]

You need to have a plan for get the heat out of the 20watt LED.
If the LED is hot its life will be short.

 

[joco000]

thx for answers.
Supply is from 12v PB, when charging circuit is not connected so input voltage is 10-14V.
this is white led, 4x4 array, datasheet say 13-14V, 1.4-1,5 A.
AN from Ti is interesting reading.
I know that making good driver is demand for longer work , I just want to have some simply driver just for temporary use, later I will do more development on that.
I am thinking make dc/dc 12 to 24, 1 pcs, and then 2 drivers for each 20w led ..buck. ??

Joe

 

[ronsimpson]

There are some very nice 110/220vac to LED at 20W circuits.