OK,
Im trying to go by the saying that the only stupid question is the one not being asked here...so please bear with me here.
I want to use ultrabright leds to make a flashlight. I was trying my hand with just one led and I wonder at the results:
Power supply: 3 AA batteries. Measured voltage was 4.6 volts
My led works at 3.6 volts and a current of 20 mA.
I have used a LED calculator and it said I need a 56 ohm resistor.
I ve measured and put the resistor up, hooked everything up and measured the current across the LED and I got to 3.0 volts.
Problem is that math/physics dont make sense here: resistance=voltage drop/current. I got a voltage drop of 1.6 (4.6-3.0) by using a resistor of 56 ohms which leads me to the conclusion that the led is getting 28 mA instead of the 20 mA (which was planned). I cant measure mAs with my digital multimeter so I cannot check that for sure.
What am I missing??
/ubbthreads/images/graemlins/mad.gif
Im trying to go by the saying that the only stupid question is the one not being asked here...so please bear with me here.
I want to use ultrabright leds to make a flashlight. I was trying my hand with just one led and I wonder at the results:
Power supply: 3 AA batteries. Measured voltage was 4.6 volts
My led works at 3.6 volts and a current of 20 mA.
I have used a LED calculator and it said I need a 56 ohm resistor.
I ve measured and put the resistor up, hooked everything up and measured the current across the LED and I got to 3.0 volts.
Problem is that math/physics dont make sense here: resistance=voltage drop/current. I got a voltage drop of 1.6 (4.6-3.0) by using a resistor of 56 ohms which leads me to the conclusion that the led is getting 28 mA instead of the 20 mA (which was planned). I cant measure mAs with my digital multimeter so I cannot check that for sure.
What am I missing??
/ubbthreads/images/graemlins/mad.gif