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
+−12 VR = ?2.1 V10 mA

A yellow LED with a forward voltage of 2.1 V runs from a 12 V supply through a series resistor. Find the resistance R that sets the LED current to 10 mA.

Vs = 12 VVF = 2.1 VI = 10 mA
R = Ω
2.Easy
+−12 VR = ?3 V20 mA

A white LED with a forward voltage of 3 V runs from a 12 V supply through a series resistor. Find the resistance R that sets the LED current to 20 mA.

Vs = 12 VVF = 3 VI = 20 mA
R = Ω
3.Medium
RC​ = 1.5 kΩβ = 80IC​ = ?RE​ = 1 kΩVCC​ = 12 VR1​ = 33 kΩR2​ = 12 kΩ

An NPN transistor with β = 80 has voltage-divider bias from VCC = 12 V: R₁ = 33 kΩ from VCC to the base and R₂ = 12 kΩ from the base to ground. The collector resistor is RC = 1.5 kΩ and the emitter resistor is RE = 1 kΩ. Take VBE = 0.7 V and use the Thévenin equivalent of the divider (do not neglect the base current). Find the collector current IC in mA.

VCC = 12 VR1 = 33 kΩR2 = 12 kΩRC = 1.5 kΩRE = 1 kΩβ = 80
IC = mA
4.Medium
RC​ = 1.2 kΩβ = 50VCC​ = 10 VRB​ = 100 kΩ

An NPN transistor with β = 50 is biased by a base resistor RB = 100 kΩ from the supply VCC = 10 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–emitter voltage VCE.

VCC = 10 VRB = 100 kΩRC = 1.2 kΩβ = 50VBE = 0.7 V
VCE = V
5.Hard
+−≥ 20 VR = ?12 V≤ 50 mA

A 12 V Zener regulator must supply up to 50 mA to a load. The input can drop to 20 V, and the Zener needs at least 1 mA to regulate. Find the largest series resistance Rmax that keeps it regulating.

Vin,min = 20 VVZ = 12 VIL,max = 50 mAIZ,min = 1 mA
Rmax = Ω
6.Hard
RC​ = 470 Ωβ = 100VCC​ = 5 V3.3 VRB​ = ?

An NPN transistor with β = 100 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 4 times the minimum needed for saturation. Find RB in kΩ.

VCC = 5 VRC = 470 Ωβ = 100Vin = 3.3 VVBE = 0.7 VVCE(sat) = 0.2 Voverdrive = 4
RB = kΩ

Answer key

  1. 1. R = 990 Ω
  2. 2. R = 450 Ω
  3. 3. IC = 2.227 mA
  4. 4. VCE = 4.42 V
  5. 5. Rmax = 156.9 Ω
  6. 6. RB = 6.365 kΩ

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