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
+−Vs​6 VR = 220 ΩD1​D2​I = ?

A 6 V DC source drives current through a 220 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 = 220 ΩVD = 0.7 V
I = mA
2.Easy
+−Vs​6 VR1​ = 680 ΩR2​ = 680 ΩID​ = ?

A 6 V DC source is connected through resistor R₁ = 680 Ω to a node X. From node X to the source’s negative terminal there are two parallel paths: resistor R₂ = 680 Ω, and a silicon diode with its anode at X. Use the constant-drop model with 0.7 V. Find the diode current ID in mA.

Vs = 6 VR1 = 680 ΩR2 = 680 ΩVD = 0.7 V
ID = mA
3.Medium
+−12 V680 Ω5.1 V1500 ΩIZ​ = ?

A 5.1 V Zener regulator is fed from 12 V through 680 Ω and supplies a 1500 Ω load. Find the Zener current IZ.

Vin = 12 VVZ = 5.1 VR = 680 ΩRL = 1500 Ω
IZ = mA
4.Medium
RC​ = 1 kΩβ = 120IC​ = ?RE​ = 1.2 kΩVCC​ = 20 VR1​ = 82 kΩR2​ = 22 kΩ

An NPN transistor with β = 120 has voltage-divider bias from VCC = 20 V: R₁ = 82 kΩ from VCC to the base and R₂ = 22 kΩ from the base to ground. The collector resistor is RC = 1 kΩ and the emitter resistor is RE = 1.2 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 = 82 kΩR2 = 22 kΩRC = 1 kΩRE = 1.2 kΩβ = 120
IC = mA
5.Hard
RC​ = 220 Ωβ = 80VCC​ = 5 V5 VRB​ = ?

An NPN transistor with β = 80 switches a 220 Ω load resistor connected between VCC = 5 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 4 times the minimum needed for saturation. Find RB in kΩ.

VCC = 5 VRC = 220 Ωβ = 80Vin = 5 VVBE = 0.7 VVCE(sat) = 0.2 Voverdrive = 4
RB = kΩ
6.Hard
RC​ = 220 Ωβ = 100VCC​ = 12 V5 VRB​ = ?

An NPN transistor with β = 100 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 4 times the minimum needed for saturation. Find RB in kΩ.

VCC = 12 VRC = 220 Ωβ = 100Vin = 5 VVBE = 0.7 VVCE(sat) = 0.2 Voverdrive = 4
RB = kΩ

Answer key

  1. 1. I = 20.91 mA
  2. 2. ID = 6.765 mA
  3. 3. IZ = 6.747 mA
  4. 4. IC = 2.607 mA
  5. 5. RB = 3.942 kΩ
  6. 6. RB = 2.004 kΩ

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