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 = ?3.2 V25 mA

A blue LED with a forward voltage of 3.2 V runs from a 24 V supply through a series resistor. Find the resistance R that sets the LED current to 25 mA.

Vs = 24 VVF = 3.2 VI = 25 mA
R = Ω
2.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
3.Medium
+−24 VR = ?2 × 3.2 V25 mA

2 blue LEDs (forward voltage 3.2 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 = 3.2 Vn = 2I = 25 mA
R = Ω
4.Medium
+−12 V330 Ω5.6 V1500 ΩIZ​ = ?

A 5.6 V Zener regulator is fed from 12 V through 330 Ω and supplies a 1500 Ω load. Find the Zener current IZ.

Vin = 12 VVZ = 5.6 VR = 330 ΩRL = 1500 Ω
IZ = mA
5.Hard
RC​ = 680 Ωβ = 100VCC​ = 9 V5 VRB​ = ?

An NPN transistor with β = 100 switches a 680 Ω load resistor connected between VCC = 9 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 10 times the minimum needed for saturation. Find RB in kΩ.

VCC = 9 VRC = 680 Ωβ = 100Vin = 5 VVBE = 0.7 VVCE(sat) = 0.2 Voverdrive = 10
RB = kΩ
6.Hard
RC​ = 1 kΩβ = 50VCC​ = 24 V3.3 VRB​ = ?

An NPN transistor with β = 50 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. 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 = 1 kΩβ = 50Vin = 3.3 VVBE = 0.7 VVCE(sat) = 0.2 V
RB = kΩ

Answer key

  1. 1. R = 832 Ω
  2. 2. R = 990 Ω
  3. 3. R = 704 Ω
  4. 4. IZ = 15.66 mA
  5. 5. RB = 3.323 kΩ
  6. 6. RB = 5.462 kΩ

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