Artificer1 Posted June 12, 2020 Share Posted June 12, 2020 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 Link to post Share on other sites More sharing options...
Suzie Posted June 12, 2020 Share Posted June 12, 2020 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. 2 2 Link to post Share on other sites More sharing options...
RMweb Premium spamcan61 Posted June 12, 2020 RMweb Premium Share Posted June 12, 2020 Resistance value doesn't have to be exact, 47 or 51 ohm will be easier to find than 50; if that's too bright then might be worth going as high as 100 ohm. 1 Link to post Share on other sites More sharing options...
Artificer1 Posted June 12, 2020 Author Share Posted June 12, 2020 Thank you , I have a selection of resistors in my ‘come in handy’ box I will try an identify a suitable rated one if not purchase a recommended. Link to post Share on other sites More sharing options...
RMweb Gold RedgateModels Posted June 12, 2020 RMweb Gold Share Posted June 12, 2020 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) 1 Link to post Share on other sites More sharing options...
meil Posted June 12, 2020 Share Posted June 12, 2020 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. 1 Link to post Share on other sites More sharing options...
Artificer1 Posted June 12, 2020 Author Share Posted June 12, 2020 Thanks to all that responded to my question. Regards Robert Link to post Share on other sites More sharing options...
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