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 V10 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 10 mA.

Vs = 5 VVF = 2.2 VI = 10 mA
R = Ω
2.Easy
+−9 V680 Ω5.1 VIR​ = ?

A 5.1 V Zener diode is fed from 9 V through a 680 Ω resistor, with no load connected. Find the current IR in the resistor.

Vin = 9 VVZ = 5.1 VR = 680 Ω
IR = mA
3.Medium
RC​ = 1.2 kΩβ = 100IC​ = ?VCC​ = 9 VRB​ = 270 kΩ

An NPN transistor with β = 100 is biased by a base resistor RB = 270 kΩ from the supply VCC = 9 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 = 9 VRB = 270 kΩRC = 1.2 kΩβ = 100VBE = 0.7 V
IC = mA
4.Medium
+−24 V270 Ω5.1 V3300 ΩIZ​ = ?

A 5.1 V Zener regulator is fed from 24 V through 270 Ω and supplies a 3300 Ω load. Find the Zener current IZ.

Vin = 24 VVZ = 5.1 VR = 270 ΩRL = 3300 Ω
IZ = mA
5.Hard
+−≥ 9 VR = ?3.3 V≤ 50 mA

A 3.3 V Zener regulator must supply up to 50 mA to a load. The input can drop to 9 V, and the Zener needs at least 2 mA to regulate. Find the largest series resistance Rmax that keeps it regulating.

Vin,min = 9 VVZ = 3.3 VIL,max = 50 mAIZ,min = 2 mA
Rmax = Ω
6.Hard
RC​ = 220 Ωβ = 80VCC​ = 5 V3.3 VRB​ = ?

An NPN transistor with β = 80 switches a 220 Ω load resistor connected between VCC = 5 V and its collector. The emitter is grounded. The base is driven from a 3.3 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 2 times the minimum needed for saturation. Find RB in kΩ.

VCC = 5 VRC = 220 Ωβ = 80Vin = 3.3 VVBE = 0.7 VVCE(sat) = 0.2 Voverdrive = 2
RB = kΩ

Answer key

  1. 1. R = 280 Ω
  2. 2. IR = 5.735 mA
  3. 3. IC = 3.074 mA
  4. 4. IZ = 68.45 mA
  5. 5. Rmax = 109.6 Ω
  6. 6. RB = 4.767 kΩ

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