metron9

02-14-2007, 05:16 PM

I decided to try the LUXEON III (3 watt) LEDS in my drumlights. The traces are big enough to carry 1.4A on the board but I am down to a 1 OHM resistor at the 5V regulated supply. Here is my problem.

I am using the IRFL110 Fet. It can handle 1.5A continuous.

I tested the RED LED and a resistor without going through the fet and I get 1240mA When I go through the FET I get 660mA

Looking at the datasheet and this is something I have not had to deal with before as I was using 7.5 ohm resistors on the LUXEON I (1 watt) LEDS

The .54 Maximum ohms RDS(on) was a small in relation to the resistor I was using. It now comes into play as a 50% difference.

I do not see minimum and typical values on the datasheet.

Question is, how do I calculate the resistor I need if I don't know the typical and minimum values, or is this a situation where increasing the voltage and resistor will lower the percentage of current drop due to the RDS(on).

The forward voltage of the red Luxeon III os 3.51V MAX and 1540mA is MAX current.

Remember too these are not 100% duty cycle so I want to push the highest current allowed to get the brightest flash.

Darn now it's 1500hrs again, always happens when I am having fun that clock just spins and spins....

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔

Think Inside the box first and if that doesn't work..

Re-arrange what's inside the box then...

Think outside the BOX!

I am using the IRFL110 Fet. It can handle 1.5A continuous.

I tested the RED LED and a resistor without going through the fet and I get 1240mA When I go through the FET I get 660mA

Looking at the datasheet and this is something I have not had to deal with before as I was using 7.5 ohm resistors on the LUXEON I (1 watt) LEDS

The .54 Maximum ohms RDS(on) was a small in relation to the resistor I was using. It now comes into play as a 50% difference.

I do not see minimum and typical values on the datasheet.

Question is, how do I calculate the resistor I need if I don't know the typical and minimum values, or is this a situation where increasing the voltage and resistor will lower the percentage of current drop due to the RDS(on).

The forward voltage of the red Luxeon III os 3.51V MAX and 1540mA is MAX current.

Remember too these are not 100% duty cycle so I want to push the highest current allowed to get the brightest flash.

Darn now it's 1500hrs again, always happens when I am having fun that clock just spins and spins....

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔

Think Inside the box first and if that doesn't work..

Re-arrange what's inside the box then...

Think outside the BOX!