Diodes & transistors worksheet with answers

Free printable Diodes & transistors worksheet: 6 problems from easy to exam level, with an answer key. Print it or save it as a PDF.

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1.Easy

A white LED with a forward voltage of 3 V runs from a 12 V supply through a series resistor. Find the resistance R that sets the LED current to 25 mA.

V_s = 12 VV_F = 3 VI = 25 mA

R = Ω

2.Easy

A 3 V DC source drives current through a 3.3 kΩ resistor in series with a forward-biased silicon diode. Use the constant-drop model with 0.7 V per conducting diode. Find the current I in mA.

V_s = 3 VR = 3.3 kΩV_D = 0.7 V

I = mA

3.Medium

A 6.2 V Zener regulator is fed from 18 V through 470 Ω and supplies a 470 Ω load. Find the Zener current I_Z.

V_in = 18 VV_Z = 6.2 VR = 470 ΩR_L = 470 Ω

I_Z = mA

4.Medium

2 white LEDs (forward voltage 3 V each) are connected in series with a resistor to a 12 V supply. Find the resistance R that sets the current to 25 mA.

V_s = 12 VV_F = 3 Vn = 2I = 25 mA

R = Ω

5.Hard

A 5.6 V Zener regulator must supply up to 40 mA to a load. The input can drop to 24 V, and the Zener needs at least 2 mA to regulate. Find the largest series resistance R_max that keeps it regulating.

V_in,min = 24 VV_Z = 5.6 VI_L,max = 40 mAI_Z,min = 2 mA

R_max = Ω

6.Hard

A 3.3 V Zener regulator must supply up to 20 mA to a load. The input can drop to 9 V, and the Zener needs at least 1 mA to regulate. Find the largest series resistance R_max that keeps it regulating.

V_in,min = 9 VV_Z = 3.3 VI_L,max = 20 mAI_Z,min = 1 mA

R_max = Ω

Answer key

1. R = 360 Ω
2. I = 0.697 mA
3. I_Z = 11.91 mA
4. R = 240 Ω
5. R_max = 438.1 Ω
6. R_max = 271.4 Ω

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