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 = ?2.1 V25 mA

A yellow LED with a forward voltage of 2.1 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 = 2.1 VI = 25 mA
R = Ω
2.Easy
+−Vs​15 VR = 680 ΩD​I = ?

A 15 V DC source drives current through a 680 Ω 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 = 15 VR = 680 ΩVD = 0.7 V
I = mA
3.Medium
RC​ = 2.2 kΩβ = 150IC​ = ?RE​ = 1 kΩVCC​ = 20 VR1​ = 56 kΩR2​ = 22 kΩ

An NPN transistor with β = 150 has voltage-divider bias from VCC = 20 V: R₁ = 56 kΩ from VCC to the base and R₂ = 22 kΩ from the base to ground. The collector resistor is RC = 2.2 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 = 20 VR1 = 56 kΩR2 = 22 kΩRC = 2.2 kΩRE = 1 kΩβ = 150
IC = mA
4.Medium
+−18 V150 Ω6.2 V3300 ΩIZ​ = ?

A 6.2 V Zener regulator is fed from 18 V through 150 Ω and supplies a 3300 Ω load. Find the Zener current IZ.

Vin = 18 VVZ = 6.2 VR = 150 ΩRL = 3300 Ω
IZ = mA
5.Hard
V (V)I (mA)0.655Q = ?

A diode is modelled as 0.6 V in series with 10 Ω (it conducts above 0.6 V). It is in series with a 1000 Ω resistor across a 5 V supply. Find the operating current ID where the diode line meets the load line.

Vs = 5 VR = 1000 ΩV0 = 0.6 Vrd = 10 Ω
ID = mA
6.Hard
+−≤ 18 V270 Ω5.6 V

A 5.6 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 = 5.6 VR = 270 Ω
PZ,max = mW

Answer key

  1. 1. R = 876 Ω
  2. 2. I = 21.03 mA
  3. 3. IC = 4.444 mA
  4. 4. IZ = 76.79 mA
  5. 5. ID = 4.356 mA
  6. 6. PZ,max = 257.2 mW

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