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​10 VR = 220 ΩD1​D2​I = ?

A 10 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 = 10 VR = 220 ΩVD = 0.7 V
I = mA
2.Easy
+−Vs​15 VR = 680 ΩD​I = ?

A 15 V DC source drives current through a 680 Ω resistor in series with a forward-biased silicon diode. Use the constant-drop model with 0.7 V per conducting diode. Find the current I in mA.

Vs = 15 VR = 680 ΩVD = 0.7 V
I = mA
3.Medium
RC​ = 2.2 kΩβ = 200IC​ = ?RE​ = 1 kΩVCC​ = 15 VR1​ = 39 kΩR2​ = 12 kΩ

An NPN transistor with β = 200 has voltage-divider bias from VCC = 15 V: R₁ = 39 kΩ from VCC to the base and R₂ = 12 kΩ from the base to ground. The collector resistor is RC = 2.2 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 current IC in mA.

VCC = 15 VR1 = 39 kΩR2 = 12 kΩRC = 2.2 kΩRE = 1 kΩβ = 200
IC = mA
4.Medium
+−12 VR = ?4 × 2.1 V5 mA

4 yellow LEDs (forward voltage 2.1 V each) are connected in series with a resistor to a 12 V supply. Find the resistance R that sets the current to 5 mA.

Vs = 12 VVF = 2.1 Vn = 4I = 5 mA
R = Ω
5.Hard
RC​ = 1 kΩβ = 100VCC​ = 9 V5 VRB​ = ?

An NPN transistor with β = 100 switches a 1 kΩ 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 = 1 kΩβ = 100Vin = 5 VVBE = 0.7 VVCE(sat) = 0.2 V
RB = kΩ
6.Hard
RC​ = 1 kΩβ = 50IC​ = ?VCC​ = 24 V5 VRB​ = 4.7 kΩ

An NPN transistor with β = 50 switches a 1 kΩ 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 = 4.7 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 = 24 VRC = 1 kΩβ = 50Vin = 5 VVBE = 0.7 VVCE(sat) = 0.2 VRB = 4.7 kΩ
IC = mA

Answer key

  1. 1. I = 39.09 mA
  2. 2. I = 21.03 mA
  3. 3. IC = 2.692 mA
  4. 4. R = 720 Ω
  5. 5. RB = 48.86 kΩ
  6. 6. IC = 23.8 mA

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