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
+−5 VR = ?2.1 V20 mA

A yellow LED with a forward voltage of 2.1 V runs from a 5 V supply through a series resistor. Find the resistance R that sets the LED current to 20 mA.

Vs = 5 VVF = 2.1 VI = 20 mA
R = Ω
2.Easy
+−Vs​3 VR = 3.3 kΩD​I = ?

A 3 V DC source drives current through a 3.3 kΩ resistor in series with a forward-biased silicon diode. Use the constant-drop model with 0.7 V per conducting diode. Find the current I in mA.

Vs = 3 VR = 3.3 kΩVD = 0.7 V
I = mA
3.Medium
+−20 V150 Ω3.3 V470 ΩIZ​ = ?

A 3.3 V Zener regulator is fed from 20 V through 150 Ω and supplies a 470 Ω load. Find the Zener current IZ.

Vin = 20 VVZ = 3.3 VR = 150 ΩRL = 470 Ω
IZ = mA
4.Medium
+−9 V680 Ω5.6 V2200 ΩIZ​ = ?

A 5.6 V Zener regulator is fed from 9 V through 680 Ω and supplies a 2200 Ω load. Find the Zener current IZ.

Vin = 9 VVZ = 5.6 VR = 680 ΩRL = 2200 Ω
IZ = mA
5.Hard
RC​ = 220 Ωβ = 200VCC​ = 12 V5 VRB​ = ?

An NPN transistor with β = 200 switches a 220 Ω load resistor connected between VCC = 12 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 3 times the minimum needed for saturation. Find RB in kΩ.

VCC = 12 VRC = 220 Ωβ = 200Vin = 5 VVBE = 0.7 VVCE(sat) = 0.2 Voverdrive = 3
RB = kΩ
6.Hard
+−≤ 22 V220 Ω6.2 V

A 6.2 V Zener regulator has a 220 Ω series resistor. The input can rise to 22 V, and the load may be disconnected. Find the largest power PZ,max the Zener must dissipate.

Vin,max = 22 VVZ = 6.2 VR = 220 Ω
PZ,max = mW

Answer key

  1. 1. R = 145 Ω
  2. 2. I = 0.697 mA
  3. 3. IZ = 104.3 mA
  4. 4. IZ = 2.455 mA
  5. 5. RB = 5.345 kΩ
  6. 6. PZ,max = 445.3 mW

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