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 V150 Ω5.6 VIR​ = ?

A 5.6 V Zener diode is fed from 24 V through a 150 Ω resistor, with no load connected. Find the current IR in the resistor.

Vin = 24 VVZ = 5.6 VR = 150 Ω
IR = mA
2.Easy
+−Vs​6 VR = 220 ΩD1​D2​I = ?

A 6 V DC source drives current through a 220 Ω resistor in series with two forward-biased silicon diodes. Use the constant-drop model with 0.7 V per conducting diode. Find the current I in mA.

Vs = 6 VR = 220 ΩVD = 0.7 V
I = mA
3.Medium
+−9 VR = ?2 × 3 V5 mA

2 white LEDs (forward voltage 3 V each) are connected in series with a resistor to a 9 V supply. Find the resistance R that sets the current to 5 mA.

Vs = 9 VVF = 3 Vn = 2I = 5 mA
R = Ω
4.Medium
RC​ = 3.3 kΩβ = 50VCC​ = 10 VRB​ = 390 kΩ

An NPN transistor with β = 50 is biased by a base resistor RB = 390 kΩ from the supply VCC = 10 V. The collector resistor is RC = 3.3 kΩ and the emitter is grounded. Take VBE = 0.7 V and assume the transistor is in the active region. Find the collector–emitter voltage VCE.

VCC = 10 VRB = 390 kΩRC = 3.3 kΩβ = 50VBE = 0.7 V
VCE = V
5.Hard
RC​ = 150 Ωβ = 50VCC​ = 24 V3.3 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 3.3 V logic output through a base resistor RB. Take VBE = 0.7 V and VCE(sat) = 0.2 V. Find the largest base resistor RB, in kΩ, that still drives the transistor just into saturation.

VCC = 24 VRC = 150 Ωβ = 50Vin = 3.3 VVBE = 0.7 VVCE(sat) = 0.2 V
RB = kΩ
6.Hard
+−≥ 24 VR = ?12 V≤ 25 mA

A 12 V Zener regulator must supply up to 25 mA to a load. The input can drop to 24 V, and the Zener needs at least 1 mA to regulate. Find the largest series resistance Rmax that keeps it regulating.

Vin,min = 24 VVZ = 12 VIL,max = 25 mAIZ,min = 1 mA
Rmax = Ω

Answer key

  1. 1. IR = 122.7 mA
  2. 2. I = 20.91 mA
  3. 3. R = 600 Ω
  4. 4. VCE = 6.065 V
  5. 5. RB = 0.8193 kΩ
  6. 6. Rmax = 461.5 Ω

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