Hi everyone,
Thx for the detailed answers but somehow i think my message didn't came across ... i'll try to explain.
First of all i ment indeed 1miliamp --> my mistake sorry
info :
- fixed resistor : 1megaohm
- potresistor : varies from 0k to 100k
- red led : VF --> starts at 1.4
- light bulb : 100 miliamp @ 6V
- supply voltage: 6V
if i put the 1 megaohm resistor in series with the trimmer (set at 100K) the led is barely shining but the voltage drop over the LED is still 1,4V and the display of my power supply shows a current of 1 miliamp or 0.001A. From other experiments i did ,it seems to be that a LED almost has a fixed voltage drop of at least 1.4V even with almost no current flowing trough it and you almost need infinite resistance to drop to 0V over the LED , is this correct what i'm thinking ??? 100 k + 1 megaohm seems not to be enough to get the LED below 1.4V
When i do the same experiment and replace the LED by a 6v lightbulb the 6v supply voltage is completely dropped over the two resistors (1 megaohm + trimpot @ 100k --> resulting in 0V reaching the lightbulb (so lightbulb not working).
I'm convinced that i'm missing something about the "working" of an LED and i miss some valuable info thats why i want your professional info.
Why is a LED so hard to shut down completely (0 V voltage drop) where as the lightbulb is 0V even with less resistance in my fixed resistors ?
Thx Mike
Thx for the detailed answers but somehow i think my message didn't came across ... i'll try to explain.
First of all i ment indeed 1miliamp --> my mistake sorry
info :
- fixed resistor : 1megaohm
- potresistor : varies from 0k to 100k
- red led : VF --> starts at 1.4
- light bulb : 100 miliamp @ 6V
- supply voltage: 6V
if i put the 1 megaohm resistor in series with the trimmer (set at 100K) the led is barely shining but the voltage drop over the LED is still 1,4V and the display of my power supply shows a current of 1 miliamp or 0.001A. From other experiments i did ,it seems to be that a LED almost has a fixed voltage drop of at least 1.4V even with almost no current flowing trough it and you almost need infinite resistance to drop to 0V over the LED , is this correct what i'm thinking ??? 100 k + 1 megaohm seems not to be enough to get the LED below 1.4V
When i do the same experiment and replace the LED by a 6v lightbulb the 6v supply voltage is completely dropped over the two resistors (1 megaohm + trimpot @ 100k --> resulting in 0V reaching the lightbulb (so lightbulb not working).
I'm convinced that i'm missing something about the "working" of an LED and i miss some valuable info thats why i want your professional info.
Why is a LED so hard to shut down completely (0 V voltage drop) where as the lightbulb is 0V even with less resistance in my fixed resistors ?
Thx Mike