voltage drop equation

Thread Starter

jonisonvespa

Joined Mar 25, 2012
49
hi
im currently trying to make a project using a ardunio uno, the outputs are 5v and the leds i want to use are surface mount 2v max 30ma current, what equation can i use to drop the voltage to 2v, 30ma?
thank you
 

Thread Starter

jonisonvespa

Joined Mar 25, 2012
49
hi mr chips im confused with the v value, is that the supply or the max voltage of the led? (supply)
ok thanks
 
Last edited:

Jess_88

Joined Apr 29, 2011
174
The way I would look at it is;
current in a series circuit is the same, while a voltage drop can be achieved across one resistor and the led in parallel with the second (same voltage in parallel).

IR1 + IR2 = 5V
IR2 = 5v-3v

...whats how I understand it anyway
 

MrChips

Joined Oct 2, 2009
30,712
Vr = 5V - 2V = 3V
R = 3V/30mA = 100 ohm

30mA for LED is too much. I would reduce it to 10mA
R = 3V/10mA = 300 ohm

Even 3mA may be bright enough
R = 3V/3mA = 1K ohm
 
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