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
+−Vs​6 VR1​ = 1 kΩR2​ = 1.5 kΩID​ = ?

A 6 V DC source is connected through resistor R₁ = 1 kΩ to a node X. From node X to the source’s negative terminal there are two parallel paths: resistor R₂ = 1.5 kΩ, 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 = 6 VR1 = 1 kΩR2 = 1.5 kΩVD = 0.7 V
ID = mA
2.Easy
+−18 V220 Ω12 VIR​ = ?

A 12 V Zener diode is fed from 18 V through a 220 Ω resistor, with no load connected. Find the current IR in the resistor.

Vin = 18 VVZ = 12 VR = 220 Ω
IR = mA
3.Medium
+−24 VR = ?5 × 3 V15 mA

5 white LEDs (forward voltage 3 V each) are connected in series with a resistor to a 24 V supply. Find the resistance R that sets the current to 15 mA.

Vs = 24 VVF = 3 Vn = 5I = 15 mA
R = Ω
4.Medium
+−12 VR = ?5 × 2.2 V20 mA

5 green LEDs (forward voltage 2.2 V each) are connected in series with a resistor to a 12 V supply. Find the resistance R that sets the current to 20 mA.

Vs = 12 VVF = 2.2 Vn = 5I = 20 mA
R = Ω
5.Hard
V (V)I (mA)0.6627.27Q = ?

A diode is modelled as 0.6 V in series with 5 Ω (it conducts above 0.6 V). It is in series with a 220 Ω resistor across a 6 V supply. Find the operating current ID where the diode line meets the load line.

Vs = 6 VR = 220 ΩV0 = 0.6 Vrd = 5 Ω
ID = mA
6.Hard
RC​ = 1 kΩβ = 50VCC​ = 9 V3.3 VRB​ = ?

An NPN transistor with β = 50 switches a 1 kΩ load resistor connected between VCC = 9 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 = 9 VRC = 1 kΩβ = 50Vin = 3.3 VVBE = 0.7 VVCE(sat) = 0.2 Voverdrive = 2
RB = kΩ

Answer key

  1. 1. ID = 4.833 mA
  2. 2. IR = 27.27 mA
  3. 3. R = 600 Ω
  4. 4. R = 50 Ω
  5. 5. ID = 24 mA
  6. 6. RB = 7.386 kΩ

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