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
+−5 VR = ?2.2 V20 mA

A green LED with a forward voltage of 2.2 V runs from a 5 V supply through a series resistor. Find the resistance R that sets the LED current to 20 mA.

Vs = 5 VVF = 2.2 VI = 20 mA
R = Ω
2.Easy
+−9 VR = ?2.1 V20 mA

A yellow LED with a forward voltage of 2.1 V runs from a 9 V supply through a series resistor. Find the resistance R that sets the LED current to 20 mA.

Vs = 9 VVF = 2.1 VI = 20 mA
R = Ω
3.Medium
RC​ = 1.2 kΩβ = 75IC​ = ?VCC​ = 12 VRB​ = 270 kΩ

An NPN transistor with β = 75 is biased by a base resistor RB = 270 kΩ from the supply VCC = 12 V. The collector resistor is RC = 1.2 kΩ and the emitter is grounded. Take VBE = 0.7 V and assume the transistor is in the active region. Find the collector current IC in mA.

VCC = 12 VRB = 270 kΩRC = 1.2 kΩβ = 75VBE = 0.7 V
IC = mA
4.Medium
RC​ = 2.2 kΩβ = 100IC​ = ?RE​ = 2.2 kΩVCC​ = 20 VR1​ = 68 kΩR2​ = 22 kΩ

An NPN transistor with β = 100 has voltage-divider bias from VCC = 20 V: R₁ = 68 kΩ from VCC to the base and R₂ = 22 kΩ from the base to ground. The collector resistor is RC = 2.2 kΩ and the emitter resistor is RE = 2.2 kΩ. Take VBE = 0.7 V and use the Thévenin equivalent of the divider (do not neglect the base current). Find the collector current IC in mA.

VCC = 20 VR1 = 68 kΩR2 = 22 kΩRC = 2.2 kΩRE = 2.2 kΩβ = 100
IC = mA
5.Hard
+−≥ 15 VR = ?9.1 V≤ 40 mA

A 9.1 V Zener regulator must supply up to 40 mA to a load. The input can drop to 15 V, and the Zener needs at least 5 mA to regulate. Find the largest series resistance Rmax that keeps it regulating.

Vin,min = 15 VVZ = 9.1 VIL,max = 40 mAIZ,min = 5 mA
Rmax = Ω
6.Hard
+−≤ 22 V100 Ω3.3 V

A 3.3 V Zener regulator has a 100 Ω series resistor. The input can rise to 22 V, and the load may be disconnected. Find the largest power PZ,max the Zener must dissipate.

Vin,max = 22 VVZ = 3.3 VR = 100 Ω
PZ,max = mW

Answer key

  1. 1. R = 140 Ω
  2. 2. R = 345 Ω
  3. 3. IC = 3.139 mA
  4. 4. IC = 1.754 mA
  5. 5. Rmax = 131.1 Ω
  6. 6. PZ,max = 617.1 mW

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