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Current Sensitive?

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axro

New Member
So correct me where I'm wrong.

Most things use what current they need and mass the rest. For instance you don't have to put a resistor inline with an IC because it uses what it needs.

Why then are LED's harmed by excess current and don't just let it pass.
 

MikeMl

Well-Known Member
Most Helpful Member
It has to do with the highly non-linear Current vs Applied Voltage curve of the LED vs an Ohmic device like a resistor.

Btw- resistors do NOT PASS current in excess of what they NEED!!! The current never flows because the current is the dependant variable; i.e. it is the RESULT. The CAUSE of current flow is the VOLTAGE applied to the resistor, and the Resistance in the circuit.

I=E/R!!!!!
 
Last edited:

axro

New Member
It has to do with the highly non-linear Current vs Applied Voltage curve of the LED vs an Ohmic device like a resistor.

Btw- resistors do NOT PASS current in excess of what they NEED!!! The current never flows because the current is the dependant variable; i.e. it is the RESULT. The CAUSE of current flow is the VOLTAGE applied to the resistor, and the Resistance in the circuit.

I=E/R!!!!!

I think we may not understand eachother.

I just meant that you could connect an IC's VCC pin to a source of power without a resistor to limit the current. Isn't that right?

Also what do you mean "The current never flows"
 

MikeMl

Well-Known Member
Most Helpful Member
I think we may not understand eachother.

I just meant that you could connect an IC's VCC pin to a source of power without a resistor to limit the current. Isn't that right?

Yes, because, by design, an IC is a device intended to be operated on a specified VOLTAGE; it draws whatever CURRENT it needs.

Contrast that to an LED, which by design is a device intended to be used at a specifed CURRENT, and when operated at that current, has a VOLTAGE across it which is determined by its internal properties.

Also what do you mean "The current never flows"

The CURRENT that flows in any circuit is the direct result of the applied VOLTAGE. There is no magic "bypassing" of excess current!!!

Look at the attachment. One battery that is being varied from 0 to 3.3V. Three parallel circuits, a simple 100 Ω resistor, an LED with no current-limiting resistor, and an LED with a 100Ω resistor in series with it...

The current through the three branches is plotted along the Y axis, while the X axis is the Battery Voltage. Note what happens to the current as the voltage ramps up. Note that the maximum safe limit for the LED Forward Current is 30mA.
 

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axro

New Member
Ok, I understand. Thanks.

I think I worded my question poorly, but you answered it. Thanks.
 
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