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 = ?3 V5 mA

A white LED with a forward voltage of 3 V runs from a 24 V supply through a series resistor. Find the resistance R that sets the LED current to 5 mA.

Vs = 24 VVF = 3 VI = 5 mA
R = Ω
2.Easy
+−Vs​10 VR1​ = 2.2 kΩR2​ = 1.5 kΩID​ = ?

A 10 V DC source is connected through resistor R₁ = 2.2 kΩ to a node X. From node X to the source’s negative terminal there are two parallel paths: resistor R₂ = 1.5 kΩ, 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 = 10 VR1 = 2.2 kΩR2 = 1.5 kΩVD = 0.7 V
ID = mA
3.Medium
RC​ = 1 kΩβ = 150RE​ = 1.5 kΩVCC​ = 15 VR1​ = 82 kΩR2​ = 22 kΩ

An NPN transistor with β = 150 has voltage-divider bias from VCC = 15 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 = 1.5 kΩ. Take VBE = 0.7 V and use the Thévenin equivalent of the divider (do not neglect the base current). Find the collector–emitter voltage VCE.

VCC = 15 VR1 = 82 kΩR2 = 22 kΩRC = 1 kΩRE = 1.5 kΩβ = 150
VCE = V
4.Medium
+−9 V100 Ω3.3 V1000 ΩIZ​ = ?

A 3.3 V Zener regulator is fed from 9 V through 100 Ω and supplies a 1000 Ω load. Find the Zener current IZ.

Vin = 9 VVZ = 3.3 VR = 100 ΩRL = 1000 Ω
IZ = mA
5.Hard
RC​ = 330 Ωβ = 100VCC​ = 9 V5 VRB​ = ?

An NPN transistor with β = 100 switches a 330 Ω load resistor connected between VCC = 9 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. Find the largest base resistor RB, in kΩ, that still drives the transistor just into saturation.

VCC = 9 VRC = 330 Ωβ = 100Vin = 5 VVBE = 0.7 VVCE(sat) = 0.2 V
RB = kΩ
6.Hard
RC​ = 150 Ωβ = 100VCC​ = 24 V5 VRB​ = ?

An NPN transistor with β = 100 switches a 150 Ω load resistor connected between VCC = 24 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 2 times the minimum needed for saturation. Find RB in kΩ.

VCC = 24 VRC = 150 Ωβ = 100Vin = 5 VVBE = 0.7 VVCE(sat) = 0.2 Voverdrive = 2
RB = kΩ

Answer key

  1. 1. R = 4200 Ω
  2. 2. ID = 3.761 mA
  3. 3. VCE = 11.18 V
  4. 4. IZ = 53.7 mA
  5. 5. RB = 16.13 kΩ
  6. 6. RB = 1.355 kΩ

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