# 4.4: Procedure

## 4.4.1: Forward Curve

1. Consider the circuit of Figure 4.3.1 using R = 1 k$$\Omega$$. For any positive value of E, the diode should be forward biased. Once E exceeds the knee voltage, the difference between the source and the knee drops across R. Thus, as E increases, so does the LED current and hence its brightness.

2. Build the circuit of Figure 4.3.1 using R = 1 k$$\Omega$$ and the red LED. Set E to 0 volts and measure both the LED voltage and current and record the results in Table 4.5.1. Note the relative brightness level. Repeat this process for the remaining source voltages listed.

3. From the data collected in Table 4.5.1, plot the current versus voltage characteristic of the forward biased LED. Make sure $$V_D$$ is the horizontal axis with $$I_D$$ on the vertical.

4. Repeat steps 2 and 3 for the blue LED using Table 4.5.2.

5. If other colors are available repeat steps 2 and 3 for them using Table 4.5.3 (create other tables as needed).

## 4.4.2: High Brightness

6. Replace the LED of Figure 4.3.1 with the high brightness white LED. Set the supply to 12 volts. Record the LED voltage, current and brightness in Table 4.5.4.

## 4.4.3: Reverse Curve

7. Consider the circuit of Figure 4.3.2 using R = 1 k$$\Omega$$. For any positive value of E, the LED should be reversed biased. In this case, the LED should always be open causing no current to flow. If no current flows, the LED produces no light. Also, the voltage across R should be zero, and thus the LED voltage should be equal to the applied source voltage. Note that the LED voltage polarity is negative with respect to that of Figure 4.3.1.

8. Build the circuit of Figure 4.3.2 using R = 1 k$$\Omega$$ using the red LED. Set E to 0 volts and measure both the LED voltage and current and record the results in Table 4.5.5. Repeat this process for the remaining source voltages listed.

9. From the data collected in Table 4.5.5, plot the current versus voltage characteristic of the reverse biased diode. Make sure $$V_D$$ is the horizontal axis with $$I_D$$ on the vertical.