Hello, I’m trying to calculate the resistor value (?,1%,1/8W) and inductor value (uH?) for the circuit attached. Using a AL8861QMP-13 and L128-5770003500000 Lumileds LEDs. Looking for resistor with same footprint as RC1206FR-071KL YAGEO, but perhaps different value? Looking for inductor with same footprint as MDWK4040T330MM, but perhaps different value?
Samman,
The LED Driver
I did find that we do carry the LED Driver here:
AL8861QMP-13 Diodes Incorporated | Integrated Circuits (ICs) | DigiKey
It looks like this LED Driver is capable of delivering 36V at 1.5A
The LED
Unfortunately, we do not carry the LED you are planning to use in the schematic. I was able to find a data sheet for it here:
DS236-luxeon-2835-color-line-datasheet.pdf (lumileds.com)
You will need to calculate the total required voltage and the total required current. Since there are three legs, and each of them will have three LEDS, we can do this as follows.
The Calculations
Each leg:
In a series configuration, voltage is additive while current remains consistent between the components.
| LED | Current | Voltage | |
|---|---|---|---|
| LED1 | 120mA | 2.7 - 3V | |
| LED2 | 120mA | 2.7 - 3V | |
| LED3 | 120mA | 2.7 - 3V | |
| LEG Total | 120mA | 8.1V - 9V |
Three legs:
In a parallel configuration, Current is additive while Voltage remains Consistent Between the components.
| LED | Current | Voltage | |
|---|---|---|---|
| LEG1 | 120mA | 8.1V - 9V | |
| LEG2 | 120mA | 8.1V - 9V | |
| LEG3 | 120mA | 8.1V - 9V | |
| LEG Total | 360mA | 8.1V - 9V |
All of the LEDs could be powered by 8.1-9V @360mA
Power Available is 36V & 1.5A
You need to reduce your voltage from 36V to 9V. This would be 1/4 of the power available working for you, the remaining 3/4 would have to be dissipated as heat.
This of course can be calculated using ohms law.
If you need assistance with that you can feel free to use this tool or any of the others available at this link:
Digikey has the calculators you need.
Online Conversion Calculators | DigiKey Electronics
I snipped the following sections of the data sheet as they support my conclusion.
The Inductor.
The calculation for this is addressed in the Data Sheet for the DC/DC regulator. Here is a snip of it.
I do hope this helps!