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### Topic: Led minimum current. (Read 25536 times)previous topic - next topic

#### polymorph

#15
##### Aug 20, 2013, 08:52 pm
Measured in what way?
Steve Greenfield AE7HD
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#### Grumpy_Mike

#16
##### Aug 21, 2013, 12:08 am

So 5V -> 100 mega-ohm resistor -> red 1.8Vf LED -> ground will result in over 1.8V being present at the LED?

Yes
Quote

Electricity is weird.

No. It would be if it worked the way you think.

It is a common beginner mistake to think that a resistor reduces voltage per say. A resistor limits current. Using two resistors can appear to reduce voltage but only due to the current flowing through them.
A 100 Meg resistor connected to 5V at one end still has 5V at the other end if no current is flowing through it. Just like a 1 Ohm resistor connected to 5V at one end still has 5V at the other end if no current is flowing through it. No current is flowing if it is not connected to anything else.

#### Henry_Best

#17
##### Aug 21, 2013, 06:02 pm

Quote

Electricity is weird.

No. It would be if it worked the way you think.

It is a common beginner mistake to think that a resistor reduces voltage per say. A resistor limits current. Using two resistors can appear to reduce voltage but only due to the current flowing through them.
A 100 Meg resistor connected to 5V at one end still has 5V at the other end if no current is flowing through it. Just like a 1 Ohm resistor connected to 5V at one end still has 5V at the other end if no current is flowing through it. No current is flowing if it is not connected to anything else.
Basic Ohms law. "The voltage across a resistor is proportional to the current flowing through it." No current = no voltage. Or, to put it another way, V=IR. If I = zero then, whatever R is, V will always be zero.

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