Introduction to Biasing

  

The goal here was to have a 9V Alkaline battery light up two LEDs with the following requirements:
                       LED1 rated 5V & 22.75mA            LED2 rated 2V & 20mA.
 LEDs were placed 'in parallel' to regulated their individual currents, with a resistor 'in series' to each LED to control their voltages. Using Kirchoff's current and voltage law we determined the ideal current, voltage, and resistors necessary, and used resistors closest to the calculated values.
                      Calculated Rs:   R1 = 176ohm     R2 = 350ohm
                      Actual Rs:         R1 = 150ohm     R2 = 360ohm
Using an ammeter and voltmeter we measured the current, voltage, and resistance of the circuit with different configuration as followed:
                      Config                    ILED1       VLED1       ILED2        VLED2      ISupply
                      Both LEDs             14.5mA   6.86V       21.0mA    1.65V      35.4mA
                      No LED2 branch    14.5mA   6.81V       X              X             14.5mA
                      No LED1 branch    X             X             20.8mA    1.65V       20.8mA
The bulbs lit up and did not explode because of too much power or current. There was a 26.4% error between the achieved LED current and the desired value, which was most likely the result of using different R values than calculated.