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
+−Vs​12 VR = 680 ΩD1​D2​I = ?

A 12 V DC source drives current through a 680 Ω resistor in series with two forward-biased silicon diodes. Use the constant-drop model with 0.7 V per conducting diode. Find the current I in mA.

Vs = 12 VR = 680 ΩVD = 0.7 V
I = mA
2.Easy
+−Vs​5 VR = 470 ΩD​I = ?

A 5 V DC source drives current through a 470 Ω 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.

Vs = 5 VR = 470 ΩVD = 0.7 V
I = mA
3.Medium
+−12 VR = ?4 × 2.2 V15 mA

4 green LEDs (forward voltage 2.2 V each) are connected in series with a resistor to a 12 V supply. Find the resistance R that sets the current to 15 mA.

Vs = 12 VVF = 2.2 Vn = 4I = 15 mA
R = Ω
4.Medium
RC​ = 2.2 kΩβ = 80VCC​ = 9 VRB​ = 560 kΩ

An NPN transistor with β = 80 is biased by a base resistor RB = 560 kΩ from the supply VCC = 9 V. The collector resistor is RC = 2.2 kΩ and the emitter is grounded. Take VBE = 0.7 V and assume the transistor is in the active region. Find the collector–emitter voltage VCE.

VCC = 9 VRB = 560 kΩRC = 2.2 kΩβ = 80VBE = 0.7 V
VCE = V
5.Hard
+−≥ 24 VR = ?5.1 V≤ 20 mA

A 5.1 V Zener regulator must supply up to 20 mA to a load. The input can drop to 24 V, and the Zener needs at least 1 mA to regulate. Find the largest series resistance Rmax that keeps it regulating.

Vin,min = 24 VVZ = 5.1 VIL,max = 20 mAIZ,min = 1 mA
Rmax = Ω
6.Hard
RC​ = 680 Ωβ = 150VCC​ = 5 V5 VRB​ = ?

An NPN transistor with β = 150 switches a 680 Ω load resistor connected between VCC = 5 V and its collector. The emitter is grounded. The base is driven from a 5 V logic output through a base resistor RB. Take VBE = 0.7 V and VCE(sat) = 0.2 V. For reliable switching, design for a base current 3 times the minimum needed for saturation. Find RB in kΩ.

VCC = 5 VRC = 680 Ωβ = 150Vin = 5 VVBE = 0.7 VVCE(sat) = 0.2 Voverdrive = 3
RB = kΩ

Answer key

  1. 1. I = 15.59 mA
  2. 2. I = 9.149 mA
  3. 3. R = 213.3 Ω
  4. 4. VCE = 6.391 V
  5. 5. Rmax = 900 Ω
  6. 6. RB = 30.46 kΩ

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