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
+−12 VR = ?2.2 V25 mA

A green LED with a forward voltage of 2.2 V runs from a 12 V supply through a series resistor. Find the resistance R that sets the LED current to 25 mA.

Vs = 12 VVF = 2.2 VI = 25 mA
R = Ω
2.Easy
+−5 VR = ?2.1 V10 mA

A yellow LED with a forward voltage of 2.1 V runs from a 5 V supply through a series resistor. Find the resistance R that sets the LED current to 10 mA.

Vs = 5 VVF = 2.1 VI = 10 mA
R = Ω
3.Medium
+−12 V220 Ω9.1 V2200 ΩIZ​ = ?

A 9.1 V Zener regulator is fed from 12 V through 220 Ω and supplies a 2200 Ω load. Find the Zener current IZ.

Vin = 12 VVZ = 9.1 VR = 220 ΩRL = 2200 Ω
IZ = mA
4.Medium
RC​ = 2.7 kΩβ = 120IC​ = ?RE​ = 2.2 kΩVCC​ = 18 VR1​ = 68 kΩR2​ = 6.8 kΩ

An NPN transistor with β = 120 has voltage-divider bias from VCC = 18 V: R₁ = 68 kΩ from VCC to the base and R₂ = 6.8 kΩ from the base to ground. The collector resistor is RC = 2.7 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 = 18 VR1 = 68 kΩR2 = 6.8 kΩRC = 2.7 kΩRE = 2.2 kΩβ = 120
IC = mA
5.Hard
+−≥ 12 VR = ?6.2 V≤ 25 mA

A 6.2 V Zener regulator must supply up to 25 mA to a load. The input can drop to 12 V, and the Zener needs at least 5 mA to regulate. Find the largest series resistance Rmax that keeps it regulating.

Vin,min = 12 VVZ = 6.2 VIL,max = 25 mAIZ,min = 5 mA
Rmax = Ω
6.Hard
+−≤ 15 V220 Ω5.6 V

A 5.6 V Zener regulator has a 220 Ω series resistor. The input can rise to 15 V, and the load may be disconnected. Find the largest power PZ,max the Zener must dissipate.

Vin,max = 15 VVZ = 5.6 VR = 220 Ω
PZ,max = mW

Answer key

  1. 1. R = 392 Ω
  2. 2. R = 290 Ω
  3. 3. IZ = 9.045 mA
  4. 4. IC = 0.4125 mA
  5. 5. Rmax = 193.3 Ω
  6. 6. PZ,max = 239.3 mW

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