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 VR = 470 ΩD1​D2​I = ?

A 6 V DC source drives current through a 470 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 = 470 ΩVD = 0.7 V
I = mA
2.Easy
+−20 V220 Ω5.1 VIR​ = ?

A 5.1 V Zener diode is fed from 20 V through a 220 Ω resistor, with no load connected. Find the current IR in the resistor.

Vin = 20 VVZ = 5.1 VR = 220 Ω
IR = mA
3.Medium
+−24 VR = ?3 × 3 V25 mA

3 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 25 mA.

Vs = 24 VVF = 3 Vn = 3I = 25 mA
R = Ω
4.Medium
RC​ = 2.7 kΩβ = 150VCC​ = 9 VRB​ = 820 kΩ

An NPN transistor with β = 150 is biased by a base resistor RB = 820 kΩ from the supply VCC = 9 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–emitter voltage VCE.

VCC = 9 VRB = 820 kΩRC = 2.7 kΩβ = 150VBE = 0.7 V
VCE = V
5.Hard
RC​ = 470 Ωβ = 200VCC​ = 5 V3.3 VRB​ = ?

An NPN transistor with β = 200 switches a 470 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 3 times the minimum needed for saturation. Find RB in kΩ.

VCC = 5 VRC = 470 Ωβ = 200Vin = 3.3 VVBE = 0.7 VVCE(sat) = 0.2 Voverdrive = 3
RB = kΩ
6.Hard
RC​ = 1 kΩβ = 100IC​ = ?VCC​ = 24 V3.3 VRB​ = 47 kΩ

An NPN transistor with β = 100 switches a 1 kΩ 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 = 47 kΩ. Take VBE = 0.7 V and VCE(sat) = 0.2 V. Find the collector current IC in mA when the input is high. Decide first whether the transistor is saturated.

VCC = 24 VRC = 1 kΩβ = 100Vin = 3.3 VVBE = 0.7 VVCE(sat) = 0.2 VRB = 47 kΩ
IC = mA

Answer key

  1. 1. I = 9.787 mA
  2. 2. IR = 67.73 mA
  3. 3. R = 600 Ω
  4. 4. VCE = 4.901 V
  5. 5. RB = 16.97 kΩ
  6. 6. IC = 5.532 mA

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