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I have a question regarding the LED reverse voltage.

A simplification of my circuit:

enter image description here

The LED is blinking as I want. It can be reverse biased when /Q is high = 5V (LED is off.) In the datasheet of the LED, it is specified that the reverse voltage is 5V.

I want to know if I have to consider this reverse voltage or not.

Klas-Kenny
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geek225
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2 Answers2

7

The LED will never be reverse biased. If /Q is high, then both terminals of the LED will be at 5V.

Reverse bias means that the cathode is more positive than the anode. This is never the case in your circuit.

  • When /Q is high, there's no voltage across the LED - both ends are at 5V, so the difference is zero. No bias.
  • When /Q is low, the cathode of the LED will be pulled towards ground through the resistor. The cathode is lower than the anode, so the LED is forward biased. The voltage drop across the LED will be (approximately) its rated forward voltage.
JRE
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4

Since the anode of your LED is on +5V and the maximum voltage on your /Q is 5V the LED is never reverse biased at all. It might have +5V on bot eand which will lead to a voltage difference across the LED of 5V.

But make sure that the /Q output has the current capability to drive the LED.

kruemi
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