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 = ?2.1 V5 mA

A yellow LED with a forward voltage of 2.1 V runs from a 24 V supply through a series resistor. Find the resistance R that sets the LED current to 5 mA.

Vs = 24 VVF = 2.1 VI = 5 mA
R = Ω
2.Easy
+−18 V220 Ω3.3 VIR​ = ?

A 3.3 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 = 3.3 VR = 220 Ω
IR = mA
3.Medium
+−12 VR = ?2 × 2 V10 mA

2 red LEDs (forward voltage 2 V each) are connected in series with a resistor to a 12 V supply. Find the resistance R that sets the current to 10 mA.

Vs = 12 VVF = 2 Vn = 2I = 10 mA
R = Ω
4.Medium
RC​ = 470 Ωβ = 200VCC​ = 10 VRB​ = 270 kΩ

An NPN transistor with β = 200 is biased by a base resistor RB = 270 kΩ from the supply VCC = 10 V. The collector resistor is RC = 470 Ω 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 = 270 kΩRC = 470 Ωβ = 200VBE = 0.7 V
VCE = V
5.Hard
RC​ = 680 Ωβ = 150VCC​ = 24 V5 VRB​ = ?

An NPN transistor with β = 150 switches a 680 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 4 times the minimum needed for saturation. Find RB in kΩ.

VCC = 24 VRC = 680 Ωβ = 150Vin = 5 VVBE = 0.7 VVCE(sat) = 0.2 Voverdrive = 4
RB = kΩ
6.Hard
V (V)I (mA)0.766Q = ?

A diode is modelled as 0.7 V in series with 50 Ω (it conducts above 0.7 V). It is in series with a 1000 Ω resistor across a 6 V supply. Find the operating current ID where the diode line meets the load line.

Vs = 6 VR = 1000 ΩV0 = 0.7 Vrd = 50 Ω
ID = mA

Answer key

  1. 1. R = 4380 Ω
  2. 2. IR = 66.82 mA
  3. 3. R = 800 Ω
  4. 4. VCE = 6.762 V
  5. 5. RB = 4.607 kΩ
  6. 6. ID = 5.048 mA

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