What resistor???

A

ANTlabs

New Member

• Oct 21, 2009

• #1

A simpol question. how do you drop 4.5 v to 3.5 v. I eed the answer bytomarow at 11:00 AM.

Thank you

 

birdman0_o

Active Member

• Oct 21, 2009

• #2

How much current, that's what were need to solve this Or what is the resistance of the load?

 

A

ANTlabs

New Member

• Oct 21, 2009

• #3

It is the 15 LED circuit again. your suggestion was 4.5 volts (AA battery).

 

birdman0_o

Active Member

• Oct 21, 2009

• #4

Ah so your LEDs are 3.5 V.... well (4.5V-3.5V)/20mA = 50 ohm resistor. You will need 15 because there are 15 leds in parallel. Understand ?

 

A

ANTlabs

New Member

• Oct 21, 2009

• #5

Wait, first of all, I want them in series. Will I rally need 15 50 ohm resistors if thy are in parallel

 

A

ANTlabs

New Member

• Oct 21, 2009

• #6

Also, I only really want to use 1 resistor.

 

audioguru

Well-Known Member

Most Helpful Member

• Oct 21, 2009

• #7

The resistor in series with an LED limits the current, it does not drop the voltage. An LED has its own voltage and could be powered from thousands of volts if the current-limiting resistor is calculated correctly.

If you connect fifteen 3.5V LEDs in series then you need 15 x 3.5= 52.5V (or more) for them plus about 5V for the single current-limiting resistor.
I don't think you have 57.5V or more.

Why did you make this new thread? It has no circuit description and no schematic so we don't know what you are talking about.

 

A

ANTlabs

New Member

• Oct 21, 2009

• #8

I need to know how to power a white LED on 4.5 volts. hat resistor should I use. As simple as that.

 

C

cbiblis

New Member

• Oct 21, 2009

• #9

see if this link helps. It's worth bookmarking. **broken link removed**

 

C

colin55

Well-Known Member

• Oct 21, 2009

• #10

I know what you are trying to say but this is entirely incorrect:

The resistor in series with an LED limits the current, it does not drop the voltage.

Click to expand...

 

birdman0_o

Active Member

• Oct 22, 2009

• #11

Perhaps the modification should be "it does not drop all the voltage"

 

audioguru

Well-Known Member

Most Helpful Member

• Oct 22, 2009

• #12

A white LED can have its current limited by a single resistor from a supply of 4.5V if you know the voltage of the LED (it is a range of voltages from 3.2V to 3.6V) and how much current you want in it.

Since you did not say what is the max allowed current in the LED, the amount of current you want in it or the voltage of the LED then we cannot help you simply calculate the value of the current-limiting resistor.