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
+−20 V330 Ω6.2 VIR​ = ?

A 6.2 V Zener diode is fed from 20 V through a 330 Ω resistor, with no load connected. Find the current IR in the resistor.

Vin = 20 VVZ = 6.2 VR = 330 Ω
IR = mA
2.Easy
+−Vs​12 VR = 2.2 kΩD​I = ?

A 12 V DC source drives current through a 2.2 kΩ 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 = 12 VR = 2.2 kΩVD = 0.7 V
I = mA
3.Medium
+−24 VR = ?3 × 2 V15 mA

3 red LEDs (forward voltage 2 V each) are connected in series with a resistor to a 24 V supply. Find the resistance R that sets the current to 15 mA.

Vs = 24 VVF = 2 Vn = 3I = 15 mA
R = Ω
4.Medium
RC​ = 1 kΩβ = 100IC​ = ?RE​ = 680 ΩVCC​ = 12 VR1​ = 22 kΩR2​ = 4.7 kΩ

An NPN transistor with β = 100 has voltage-divider bias from VCC = 12 V: R₁ = 22 kΩ from VCC to the base and R₂ = 4.7 kΩ from the base to ground. The collector resistor is RC = 1 kΩ and the emitter resistor is RE = 680 Ω. 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 = 12 VR1 = 22 kΩR2 = 4.7 kΩRC = 1 kΩRE = 680 Ωβ = 100
IC = mA
5.Hard
RC​ = 100 Ωβ = 200IC​ = ?VCC​ = 9 V3.3 VRB​ = 10 kΩ

An NPN transistor with β = 200 switches a 100 Ω load resistor connected between VCC = 9 V and its collector. The emitter is grounded. The base is driven from a 3.3 V logic output through a base resistor RB = 10 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 = 100 Ωβ = 200Vin = 3.3 VVBE = 0.7 VVCE(sat) = 0.2 VRB = 10 kΩ
IC = mA
6.Hard
RC​ = 150 Ωβ = 100VCC​ = 12 V5 VRB​ = ?

An NPN transistor with β = 100 switches a 150 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 = 150 Ωβ = 100Vin = 5 VVBE = 0.7 VVCE(sat) = 0.2 Voverdrive = 2
RB = kΩ

Answer key

  1. 1. IR = 41.82 mA
  2. 2. I = 5.136 mA
  3. 3. R = 1200 Ω
  4. 4. IC = 1.947 mA
  5. 5. IC = 52 mA
  6. 6. RB = 2.733 kΩ

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