Direct driving of SMD LEDs

Questions and discussion about The WiPy 1.0 board and CC3200 boards.
Target audience: Users with a WiPy 1.0 or CC3200 board.
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danielm
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Direct driving of SMD LEDs

Post by danielm » Wed Jun 29, 2016 12:18 pm

Do you think that it is safe to directly drive SMD LEDs with 5mA operating current from output pins of CC3200? It should handle up to 6mA.
I am asking because heartbeat LED on WiPy is driven through MOSFET.

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pythoncoder
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Re: Direct driving of SMD LEDs

Post by pythoncoder » Wed Jun 29, 2016 4:58 pm

In general it's only safe to drive an LED via a limiting resistor. If the WiPy output is rated at 5mA/3.3V, a red LED will drop about 1.7V. So the resistor you need is (3.3 -1.7)/0.005 = 330 ohms (nearest preferred value).

Note I haven't checked the WiPy specs and LED voltage drops depend on colour but this should give a pointer as to how to calculate the value. A MOSFET would enable you to put more current through the LED.
Peter Hinch

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