Thx guys for the new info. I will study this today and let it all sink in. I'll probably have a few more questions this evening.
Your input is very much appreciated!!
Your input is very much appreciated!!
The datasheet seems to indicate that the AL8843 will output a max of 3A. Am I missing something?@johnaustinkaty
The AL8843 will not produce a PWM output @ 450mA, it uses the input PWM signal to adjust brightness by changing the average output current.
The LEDs are CREE XLamp, XPE2, Red-Orange. There are three LEDs prewired in series.Lots of conflicting and some incorrect info in this thread.
Listen to Ian0 in post #3. or LesJones in post #4. They are essentially saying the same thing.
You want to drive the LEDs with a constant current of 450mA. Putting them in series does this with just one driver, whereas 3 would be required if you did it in parallel. They will need a supply that can provide constant current or 450mA at 21V.
Bob
It sounds like the AL8843 is the IC version of the LD24AJTA module. Am I right?To set the LED current to 450 mA Rset on the application circuit in the AL8843 data sheet will need to be 0.22 ohm.
Yo can control the brightness by connecting the PWM output from the ATtiny85 to the control input of the AL8843.
If your total load on the +5 volt rail is only 40 mA you will only waste 280 mW using a linear regulator. You could use an LM78L05 which is smaller than an LM7805. I think designing your own switching regulator based on an Arduino would waste more power than a linear regulator. If you want to use a switching regulator an MC4063 is one possible solution.
Les.
450mA would be the maximum when pulse width is 255 (100%).@johnaustinkaty
The AL8843 will not produce a PWM output @ 450mA, it uses the input PWM signal to adjust brightness by changing the average output current.
I agree. I was wondering if the circuit on the LD24AJTA module might be similar to the circuitry inside the ALL8843 IC, basically accomplishing the same thing?I don't think so. I can find no data on the LD24AJTA module. It does not look like it uses the AL8843 chip.
Les.
That chart is for analog dimming.Here is the graph from the AL8843 data sheet:
View attachment 243946
That chart is for analog dimming.
Aren't you using PWM dimming?
If so..
Rset=0.17 ohms
L=47uh, 0.2ohm
Fsw=376.7Khz
PWM_freq=500Hz (or less)
DC max=67% for 600ma
The values were generated using their calculator.
As I'm using PWM, that would eliminate the need for parallel resistors to dissipate power as heat, right?Yes, I am providing the PWM pulse from the attiny IC to the CTRL pin on the AL8843.
you won’t need LED current limit resistor(s)As I'm using PWM, that would eliminate the need for parallel resistors to dissipate power as heat, right?
I'm learning so much from you guys, thank you.
Awesome. I'm taking them out. I'll post my schematic and board shortly. Please be kind LOL. I am NOT an electrical designer, but it makes sense to me. This is six weeks of work for me. I welcome any and all input/recommendations of course.you won’t need LED current limit resistor(s)
by Don Wilcher
by Jake Hertz
by Jake Hertz