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​5 VR = 330 ΩD1​D2​I = ?

A 5 V DC source drives current through a 330 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 = 5 VR = 330 ΩVD = 0.7 V
I = mA
2.Easy
+−5 VR = ?2 V5 mA

A red LED with a forward voltage of 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 = 2 VI = 5 mA
R = Ω
3.Medium
RC​ = 2.7 kΩβ = 50VCC​ = 12 VRB​ = 390 kΩ

An NPN transistor with β = 50 is biased by a base resistor RB = 390 kΩ from the supply VCC = 12 V. The collector resistor is RC = 2.7 kΩ and the emitter is grounded. Take VBE = 0.7 V and assume the transistor is in the active region. Find the collector–emitter voltage VCE.

VCC = 12 VRB = 390 kΩRC = 2.7 kΩβ = 50VBE = 0.7 V
VCE = V
4.Medium
RC​ = 1 kΩβ = 80IC​ = ?RE​ = 1.5 kΩVCC​ = 20 VR1​ = 82 kΩR2​ = 12 kΩ

An NPN transistor with β = 80 has voltage-divider bias from VCC = 20 V: R₁ = 82 kΩ from VCC to the base and R₂ = 12 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 current IC in mA.

VCC = 20 VR1 = 82 kΩR2 = 12 kΩRC = 1 kΩRE = 1.5 kΩβ = 80
IC = mA
5.Hard
RC​ = 150 Ωβ = 150VCC​ = 9 V5 VRB​ = ?

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. Take VBE = 0.7 V and VCE(sat) = 0.2 V. For reliable switching, design for a base current 3 times the minimum needed for saturation. Find RB in kΩ.

VCC = 9 VRC = 150 Ωβ = 150Vin = 5 VVBE = 0.7 VVCE(sat) = 0.2 Voverdrive = 3
RB = kΩ
6.Hard
RC​ = 470 Ωβ = 200IC​ = ?VCC​ = 12 V3.3 VRB​ = 1 kΩ

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 3.3 V logic output through a base resistor RB = 1 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 = 12 VRC = 470 Ωβ = 200Vin = 3.3 VVBE = 0.7 VVCE(sat) = 0.2 VRB = 1 kΩ
IC = mA

Answer key

  1. 1. I = 10.91 mA
  2. 2. R = 600 Ω
  3. 3. VCE = 8.088 V
  4. 4. IC = 1.123 mA
  5. 5. RB = 3.665 kΩ
  6. 6. IC = 25.11 mA

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