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Dimmable LED


This is the AQA version closing after June 2019. Visit the the version for Eduqas instead.

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Build the Circuit and Adjust the Potentiometer

  1. Measure the voltage across the LED.
     
  2. Measure the current through the LED.
     
  3. Plot a graph of your measurements.
     
  4. At what voltage does the LED start glowing?

    HIGH FLYERS
     
  5. Try red, yellow and green LEDs. Are the voltages different?
     
  6. Try an Infrared LED.

Power Conntections

Dimmable LED Circuit

Led Dimmer Circuit Layout

The Layout

Layout Photo

Adding the Meters

Layout with Meters

The Graph

The LED is at risk with negative or reverse bias voltages. If the voltage is too great, the LED could be destroyed.

Note that there are few measurements in the straight non-interesting parts of the graphs and lots of measurements where the graphs turn the corner. This is good scientific technique.

LED Graph

5.1 Volt Zener Diode Characteristics - Advanced Task

The same test circuit can be used but drop the 680Ω resistors down to 330Ω to increase the currents a little.

This graph shows the Zener voltage becoming significantly inaccurate below 10mA.

Zener Diode Characteristics

 

 

 

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