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1.8 - 2.2V Supply .


Artificer1
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I have recently purchased ‘micro litz wired leads SMD LEDS’ the packaging advised 2.8 - 3.4 V supply , however when applied from 2 X 1.5 v batteries LEDs failed. Supplier now advises supply voltage should be 1.8 - 2.2V . Can someone advise how to reduce voltage . Regards Robert

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You will need to use a series resistor. It sounds like your LED is of the red, yellow, orange, or wishy-washy green type and 3V will be too much for it without any current limiting.

 

Assuming that you would like to stick with your 2x 1.5V cells, and assuming that the LED forward voltage is around 2V, and assuming that a current of 20mA will give adequate brightness, I propose the following resistor using the formula R=V/I :-

 

((2x1.5) - 2) / 0.02 = 50R

 

Just connect a 50 Ohm resistor in series with your LED and power it from your two 1.5V cells.

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You can also use Suzie's formula to work out resistor values for other supply voltages

 

12v for example - (12 - 2) / 0.02 = 500 ohms  (although as a general rule of thumb I always use a 1K ohm resistor for 12v)

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1 hour ago, Artificer1 said:

I have recently purchased ‘micro litz wired leads SMD LEDS’ the packaging advised 2.8 - 3.4 V supply , however when applied from 2 X 1.5 v batteries LEDs failed. Supplier now advises supply voltage should be 1.8 - 2.2V . Can someone advise how to reduce voltage . Regards Robert

First off it is not 2.8 - 3.4V supply. That is the voltage drop across the LED. The LED requires a resistor in series to control the current. There is no need to use 2x1.5v batteries, you can use 12v DC and a 1k resistor.

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