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 = ?3 V10 mA

A white LED with a forward voltage of 3 V runs from a 5 V supply through a series resistor. Find the resistance R that sets the LED current to 10 mA.

Vs = 5 VVF = 3 VI = 10 mA
R = Ω
2.Easy
+−Vs​9 VR = 1 kΩD1​D2​I = ?

A 9 V DC source drives current through a 1 kΩ 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 = 9 VR = 1 kΩVD = 0.7 V
I = mA
3.Medium
+−9 VR = ?2 × 3.2 V20 mA

2 blue LEDs (forward voltage 3.2 V each) are connected in series with a resistor to a 9 V supply. Find the resistance R that sets the current to 20 mA.

Vs = 9 VVF = 3.2 Vn = 2I = 20 mA
R = Ω
4.Medium
+−18 V680 Ω5.1 V2200 ΩIZ​ = ?

A 5.1 V Zener regulator is fed from 18 V through 680 Ω and supplies a 2200 Ω load. Find the Zener current IZ.

Vin = 18 VVZ = 5.1 VR = 680 ΩRL = 2200 Ω
IZ = mA
5.Hard
RC​ = 680 Ωβ = 80VCC​ = 12 V5 VRB​ = ?

An NPN transistor with β = 80 switches a 680 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 5 times the minimum needed for saturation. Find RB in kΩ.

VCC = 12 VRC = 680 Ωβ = 80Vin = 5 VVBE = 0.7 VVCE(sat) = 0.2 Voverdrive = 5
RB = kΩ
6.Hard
+−≤ 18 V270 Ω9.1 V

A 9.1 V Zener regulator has a 270 Ω series resistor. The input can rise to 18 V, and the load may be disconnected. Find the largest power PZ,max the Zener must dissipate.

Vin,max = 18 VVZ = 9.1 VR = 270 Ω
PZ,max = mW

Answer key

  1. 1. R = 200 Ω
  2. 2. I = 7.6 mA
  3. 3. R = 130 Ω
  4. 4. IZ = 16.65 mA
  5. 5. RB = 3.965 kΩ
  6. 6. PZ,max = 300 mW

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