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 = ?3.2 V5 mA

A blue LED with a forward voltage of 3.2 V runs from a 5 V supply through a series resistor. Find the resistance R that sets the LED current to 5 mA.

Vs = 5 VVF = 3.2 VI = 5 mA
R = Ω
2.Easy
+−15 V220 Ω5.1 VIR​ = ?

A 5.1 V Zener diode is fed from 15 V through a 220 Ω resistor, with no load connected. Find the current IR in the resistor.

Vin = 15 VVZ = 5.1 VR = 220 Ω
IR = mA
3.Medium
RC​ = 1 kΩβ = 120RE​ = 1 kΩVCC​ = 20 VR1​ = 22 kΩR2​ = 8.2 kΩ

An NPN transistor with β = 120 has voltage-divider bias from VCC = 20 V: R₁ = 22 kΩ from VCC to the base and R₂ = 8.2 kΩ from the base to ground. The collector resistor is RC = 1 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–emitter voltage VCE.

VCC = 20 VR1 = 22 kΩR2 = 8.2 kΩRC = 1 kΩRE = 1 kΩβ = 120
VCE = V
4.Medium
RC​ = 2.2 kΩβ = 80IC​ = ?RE​ = 1.2 kΩVCC​ = 20 VR1​ = 33 kΩR2​ = 22 kΩ

An NPN transistor with β = 80 has voltage-divider bias from VCC = 20 V: R₁ = 33 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 = 1.2 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 = 33 kΩR2 = 22 kΩRC = 2.2 kΩRE = 1.2 kΩβ = 80
IC = mA
5.Hard
RC​ = 150 Ωβ = 150IC​ = ?VCC​ = 9 V5 VRB​ = 47 kΩ

An NPN transistor with β = 150 switches a 150 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 = 47 kΩ. Take VBE = 0.7 V and VCE(sat) = 0.2 V. Find the collector current IC in mA when the input is high. Decide first whether the transistor is saturated.

VCC = 9 VRC = 150 Ωβ = 150Vin = 5 VVBE = 0.7 VVCE(sat) = 0.2 VRB = 47 kΩ
IC = mA
6.Hard
RC​ = 470 Ωβ = 200VCC​ = 12 V5 VRB​ = ?

An NPN transistor with β = 200 switches a 470 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 2 times the minimum needed for saturation. Find RB in kΩ.

VCC = 12 VRC = 470 Ωβ = 200Vin = 5 VVBE = 0.7 VVCE(sat) = 0.2 Voverdrive = 2
RB = kΩ

Answer key

  1. 1. R = 360 Ω
  2. 2. IR = 45 mA
  3. 3. VCE = 11.02 V
  4. 4. IC = 5.29 mA
  5. 5. IC = 13.72 mA
  6. 6. RB = 17.13 kΩ

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