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3mm and 5mm LED

Electrical Engineering Asked by user29463 on February 20, 2021

Why can’t we use a 5mm LED as the flasher in this circuit? What’s the difference between a 3 mm and 5 mm led? How do you identify one?

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3 Answers

Note that the paragraph that accompanies the circuit specifies the LED type as a flashing LED. It says that a normal LED will not work. The paragraph does state that the LED in the picture is 3mm, so I can understand the confusion. However, a flashing LED has a small circuit built in to make it self-flashing.

This circuit needs that internal circuitry of the flashing LED to drive the NPN transistor.

In summary, if you can find a 5mm flashing LED, you can go ahead and use it! Just make sure it is a flashing LED though! A quick Google of flashing LEDs will give you numerous results with different sizes.

Answered by MCG on February 20, 2021

Any size LED will work - the warning is that it needs to be a flasher type LED, since it relies on the current drawn by the flashing LED to drive the transistor switching the other one.

Answered by Phil G on February 20, 2021

Nothing in that says it needs to be 3mm. However it does say an ORDINARY LED will not work (You need a flashing LED).

Answered by DKNguyen on February 20, 2021

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