Help Needed !!! dimmable 23v @ 2.1A

[siaug18]

This is my first post here! hope some one can help. ok here goes;

I have a supply of 12v @ 6A

I need to drive a led bank 7 led in series * 20 parallel = 140 led total

each led has a forward of 3.1v @ 150mA


so thats a voltage of 21.7V @ 2.1A (22-23v @ 3A would be perfect)

I would also like the driver to be dimmable with PWM or a anologue voltage.

one big problem is that i dont want the driver to get too hot ....

I think i will need a boost type driver but I am unable to find a driver that can boost my voltage and offer me the current i need.

any help would be a great help...

 

[saabluster]

This is my first post here! hope some one can help. ok here goes;

I have a supply of 12v @ 6A

I need to drive a led bank 7 led in series * 20 parallel = 140 led total

each led has a forward of 3.1v @ 150mA


so thats a voltage of 21.7V @ 2.1A (22-23v @ 3A would be perfect)

I would also like the driver to be dimmable with PWM or a anologue voltage.

one big problem is that i dont want the driver to get too hot ....

I think i will need a boost type driver but I am unable to find a driver that can boost my voltage and offer me the current i need.

any help would be a great help...

You will get more help if you post this in the proper forum. Try to get a Mod to move this to the "Flashlight Electronics" forum. And :welcome:

 

[DM51]

Welcome to CPF, siaug18.

I'll move the thread for you as Saabluster has suggested.

 

[mpf]

For a basic non-dimmable supply try a note book power supply designed to run from 12V (i.e. car battery) You should be able to find one that supplies 22V at 2.5A

For a dimmable PWM you could use TaskLed's D2Dim http://www.taskled.com/d2flex.html driven by the above supply.

For a full blown solution look at LTC3783 (you could just use their sample design supplied in their Spice simulator with a little tweeking)
http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1003,C1042,C1031,C1115,P15692

matthew

 

[Mr Happy]

This is my first post here! hope some one can help. ok here goes;

I have a supply of 12v @ 6A

I need to drive a led bank 7 led in series * 20 parallel = 140 led total

each led has a forward of 3.1v @ 150mA


so thats a voltage of 21.7V @ 2.1A (22-23v @ 3A would be perfect)

I would also like the driver to be dimmable with PWM or a anologue voltage.

one big problem is that i dont want the driver to get too hot ....

I think i will need a boost type driver but I am unable to find a driver that can boost my voltage and offer me the current i need.

any help would be a great help...

Before you look for a supply I think you need to make sure that what you want to do is feasible.

First of all it does not look like your numbers add up.

7 x 3.1 = 21.7 V so that looks OK.

But 20 x 0.15 = 3 A, not 2.1 A.

If we look at the power, 21.7 x 3 = 65.1 W

Assuming you need a driver to boost the voltage, there is a need to allow for inefficiencies and provide a margin of error. An efficiency of 80% would be a reasonable allowance, so that would bring the power requirement to

65.1 / 0.8 = 81 W

Your power supply is 12 V @ 6 A = 72 W.

So it seems marginal that you could obtain what you need from a driver with that power supply. You may need to run the LEDs at a lower current or use a larger power supply or something.

 

[siaug18]

sorry about the bad math! I had worked it out to be 3A ... thanks any way.

What I think i will do is split the bank and use 2 ltc3783 Circuits and run the pwm from a pic micro...

I will order in all the parts today and build up a development board to test !

I will post my results as soon as I have any !

Thanks again

:0)