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 = ?2.1 V25 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 25 mA.

Vs = 5 VVF = 2.1 VI = 25 mA
R = Ω
2.Easy
+−24 V330 Ω5.6 VIR​ = ?

A 5.6 V Zener diode is fed from 24 V through a 330 Ω resistor, with no load connected. Find the current IR in the resistor.

Vin = 24 VVZ = 5.6 VR = 330 Ω
IR = mA
3.Medium
RC​ = 2.7 kΩβ = 50IC​ = ?VCC​ = 15 VRB​ = 270 kΩ

An NPN transistor with β = 50 is biased by a base resistor RB = 270 kΩ from the supply VCC = 15 V. The collector resistor is RC = 2.7 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 = 15 VRB = 270 kΩRC = 2.7 kΩβ = 50VBE = 0.7 V
IC = mA
4.Medium
RC​ = 1.5 kΩβ = 150IC​ = ?RE​ = 1.2 kΩVCC​ = 15 VR1​ = 33 kΩR2​ = 15 kΩ

An NPN transistor with β = 150 has voltage-divider bias from VCC = 15 V: R₁ = 33 kΩ from VCC to the base and R₂ = 15 kΩ from the base to ground. The collector resistor is RC = 1.5 kΩ and the emitter resistor is RE = 1.2 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 = 15 VR1 = 33 kΩR2 = 15 kΩRC = 1.5 kΩRE = 1.2 kΩβ = 150
IC = mA
5.Hard
+−≥ 20 VR = ?5.6 V≤ 50 mA

A 5.6 V Zener regulator must supply up to 50 mA to a load. The input can drop to 20 V, and the Zener needs at least 5 mA to regulate. Find the largest series resistance Rmax that keeps it regulating.

Vin,min = 20 VVZ = 5.6 VIL,max = 50 mAIZ,min = 5 mA
Rmax = Ω
6.Hard
RC​ = 150 Ωβ = 50VCC​ = 24 V5 VRB​ = ?

An NPN transistor with β = 50 switches a 150 Ω load resistor connected between VCC = 24 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 10 times the minimum needed for saturation. Find RB in kΩ.

VCC = 24 VRC = 150 Ωβ = 50Vin = 5 VVBE = 0.7 VVCE(sat) = 0.2 Voverdrive = 10
RB = kΩ

Answer key

  1. 1. R = 116 Ω
  2. 2. IR = 55.76 mA
  3. 3. IC = 2.648 mA
  4. 4. IC = 3.123 mA
  5. 5. Rmax = 261.8 Ω
  6. 6. RB = 0.1355 kΩ

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