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
+−24 VR = ?3 V20 mA

A white LED with a forward voltage of 3 V runs from a 24 V supply through a series resistor. Find the resistance R that sets the LED current to 20 mA.

Vs = 24 VVF = 3 VI = 20 mA
R = Ω
2.Easy
+−Vs​9 VR1​ = 470 ΩR2​ = 680 ΩID​ = ?

A 9 V DC source is connected through resistor R₁ = 470 Ω to a node X. From node X to the source’s negative terminal there are two parallel paths: resistor R₂ = 680 Ω, and a silicon diode with its anode at X. Use the constant-drop model with 0.7 V. Find the diode current ID in mA.

Vs = 9 VR1 = 470 ΩR2 = 680 ΩVD = 0.7 V
ID = mA
3.Medium
RC​ = 1.5 kΩβ = 200IC​ = ?RE​ = 680 ΩVCC​ = 12 VR1​ = 22 kΩR2​ = 4.7 kΩ

An NPN transistor with β = 200 has voltage-divider bias from VCC = 12 V: R₁ = 22 kΩ from VCC to the base and R₂ = 4.7 kΩ from the base to ground. The collector resistor is RC = 1.5 kΩ and the emitter resistor is RE = 680 Ω. 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 = 12 VR1 = 22 kΩR2 = 4.7 kΩRC = 1.5 kΩRE = 680 Ωβ = 200
IC = mA
4.Medium
+−15 V150 Ω5.1 V1500 ΩIZ​ = ?

A 5.1 V Zener regulator is fed from 15 V through 150 Ω and supplies a 1500 Ω load. Find the Zener current IZ.

Vin = 15 VVZ = 5.1 VR = 150 ΩRL = 1500 Ω
IZ = mA
5.Hard
+−≤ 24 V220 Ω3.3 V

A 3.3 V Zener regulator has a 220 Ω series resistor. The input can rise to 24 V, and the load may be disconnected. Find the largest power PZ,max the Zener must dissipate.

Vin,max = 24 VVZ = 3.3 VR = 220 Ω
PZ,max = mW
6.Hard
+−≥ 18 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 18 V, and the Zener needs at least 5 mA to regulate. Find the largest series resistance Rmax that keeps it regulating.

Vin,min = 18 VVZ = 5.1 VIL,max = 20 mAIZ,min = 5 mA
Rmax = Ω

Answer key

  1. 1. R = 1050 Ω
  2. 2. ID = 16.63 mA
  3. 3. IC = 2.01 mA
  4. 4. IZ = 62.6 mA
  5. 5. PZ,max = 310.5 mW
  6. 6. Rmax = 516 Ω

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