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
+−9 VR = ?3.2 V25 mA

A blue LED with a forward voltage of 3.2 V runs from a 9 V supply through a series resistor. Find the resistance R that sets the LED current to 25 mA.

Vs = 9 VVF = 3.2 VI = 25 mA
R = Ω
2.Easy
+−Vs​6 VR = 680 ΩD1​D2​I = ?

A 6 V DC source drives current through a 680 Ω 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 = 6 VR = 680 ΩVD = 0.7 V
I = mA
3.Medium
RC​ = 2.7 kΩβ = 200IC​ = ?RE​ = 2.2 kΩVCC​ = 20 VR1​ = 39 kΩR2​ = 22 kΩ

An NPN transistor with β = 200 has voltage-divider bias from VCC = 20 V: R₁ = 39 kΩ from VCC to the base and R₂ = 22 kΩ from the base to ground. The collector resistor is RC = 2.7 kΩ and the emitter resistor is RE = 2.2 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 = 39 kΩR2 = 22 kΩRC = 2.7 kΩRE = 2.2 kΩβ = 200
IC = mA
4.Medium
+−9 V220 Ω6.2 V1500 ΩIZ​ = ?

A 6.2 V Zener regulator is fed from 9 V through 220 Ω and supplies a 1500 Ω load. Find the Zener current IZ.

Vin = 9 VVZ = 6.2 VR = 220 ΩRL = 1500 Ω
IZ = mA
5.Hard
+−≥ 9 VR = ?5.1 V≤ 10 mA

A 5.1 V Zener regulator must supply up to 10 mA to a load. The input can drop to 9 V, and the Zener needs at least 2 mA to regulate. Find the largest series resistance Rmax that keeps it regulating.

Vin,min = 9 VVZ = 5.1 VIL,max = 10 mAIZ,min = 2 mA
Rmax = Ω
6.Hard
RC​ = 100 Ωβ = 150VCC​ = 5 V3.3 VRB​ = ?

An NPN transistor with β = 150 switches a 100 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 = 100 Ωβ = 150Vin = 3.3 VVBE = 0.7 VVCE(sat) = 0.2 Voverdrive = 4
RB = kΩ

Answer key

  1. 1. R = 232 Ω
  2. 2. I = 6.765 mA
  3. 3. IC = 2.855 mA
  4. 4. IZ = 8.594 mA
  5. 5. Rmax = 325 Ω
  6. 6. RB = 2.031 kΩ

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