Hi everyone,

just finished my Bsc and i really want to get better at designing.
found out LTspice is great for beginners and so i need to understand some key factors at designing in CAD.

my project is DIY Led grow light and i already faced something that bothering me and i cant figure it out..

the diodes that i want to use are samsung LM301B.
the data sheets say the at 2.7 VDC a single diode should draw 50mA, when i tried to simulate it in LTSPICE the diode draws 1.2 TA!!!
now i know that usually you need to place a resistor in series to reduce the current.

should i do the same here? or am i doing something wrong?

 

You never apply a DC voltage to an LED because it is a diode that has a certain voltage at a certain current at a certain temperature. If the voltage you apply is slightly higher then the LED draws a massive current and is destroyed.

You connect a series resistor or current-limiting circuit and use Ohm's Law to calculate the voltage needed for the LED plus resistor. Then Ohm's Law is used to calculate the resistor value and its power rating.

The datasheet for the Samsung LM301B shows that its forward voltage is a range of voltages like all other LEDs, it is from 2.6V to 2.9V but only at 25 degrees C. Its forward voltage changes when it is powered and gets hot.