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Transcript
Running Head: Resistor Bias of LEDs 1 LED Biasing Fundamentals Resistor Bias of LEDs In this lab you will create a constant current source using a voltage divider biased bipolar transistor and compare to a resistor biased circuit. For each circuit three different loads consisting of a red, green and blue LED will be used. In this section we will look at a simple resistor bias and the effect on current in a circuit when an LED is replaced with another LED of different colour. Niagara College Photonics Engineering Technology No sector of business or industry remains untouched by photonics, the science of generating and harnessing light. The Photonics Engineering Technology program at Niagara College encompasses optics, lasers, electro-optics, spectroscopy and electronics technology. Resistor Bias of LEDs 2 Document content developed by: Alexander McGlashan Niagara College of Applied Arts and Technology School of Technology, Department of Photonics Resistor Bias of LEDs Purpose In this lab you will create a constant current source using a voltage divider biased bipolar transistor and compare to a resistor biased circuit. For each circuit three different loads consisting of a red, green and blue LED will be used. In this section we will look at a simple resistor bias and the effect on current in a circuit when an LED is replaced with another LED of different colour. Multisim Simulation - Resistor Biased LED 1. Open the Multisim file: Resistor Biased LED LED1 is a red LED LED2 is a green LED LED3 is a blue LED 2. If a red x appears next to the myDAQ DMM instrument as shown, double click the x to activate the instrument. 3 Resistor Bias of LEDs The DMM should now appear as shown: 4 Resistor Bias of LEDs 5 3. Create a table in your log book and Excel as shown: LED Forward Voltage Drop LED Current LED 1 LED 2 LED 3 4. Connect LED1 in series with R1 and the 15V supply on the myDAQ as shown: 5. Measure the voltage across and the current through the LED and record the measurements in your tables. Resistor Bias of LEDs 6 Resistor Bias of LEDs 7 6. Repeat the measurements for LED2 and LED3. Your table should appear similar to: LED Forward Voltage Drop (V) LED Current (mA) LED 1 1.80 13.20 LED 2 2.10 12.91 LED 3 3.41 11.60 7. Graph your results. Note that as you changed the LED (each with a different forward voltage drop) the current through the circuit changed. Resistor Bias of LEDs 8 16.00 14.00 12.00 10.00 LED Current 8.00 (mA) Series1 6.00 4.00 2.00 0.00 0.00 1.00 2.00 3.00 4.00 LED Voltage (V) 8. Create a second red LED and connect it in series with LED1 and the resistor as shown. Measure and record the current. Resistor Bias of LEDs 9 9. Try adding a third red LED and then a fourth. Record the current in each case and generate a table of data and create a line graph showing the results. LED Current (mA) One LED 13.20 Two LEDs Three LEDs 11.41 Four LEDs 7.89 9.63 14.00 12.00 10.00 8.00 LED Current (mA) 6.00 Series1 4.00 2.00 0.00 One LED Two LEDs Three LEDs Four LEDs 10. If these were real LEDs, what would happen to the brightness of the LEDs as you continue to add more LEDs in series? 11. Comment on the stability of current in regards to changing load (the LEDs) conditions. (Is the current stable with a change in load?) Resistor Bias of LEDs myDAQ Resistor Biased LED Parts Required: 1 – 1kΩ resistor 4 – Red LEDs 1 – Green LED 1 – Blue LED 1. Repeat the experiment as described in the simulation using the myDAQ. Compare the measured results to your simulated results. Explain any discrepancies. 2. Is the current stable as you change the colour of the LED? Is the current stable as you add additional LEDs to the circuit? Explain your answer. 10