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
+−12 V100 Ω3.3 VIR​ = ?

A 3.3 V Zener diode is fed from 12 V through a 100 Ω resistor, with no load connected. Find the current IR in the resistor.

Vin = 12 VVZ = 3.3 VR = 100 Ω
IR = mA
2.Easy
+−Vs​15 VR1​ = 1.5 kΩR2​ = 680 ΩID​ = ?

A 15 V DC source is connected through resistor R₁ = 1.5 kΩ to a node X. From node X to the source’s negative terminal there are two parallel paths: resistor R₂ = 680 Ω, 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 = 15 VR1 = 1.5 kΩR2 = 680 ΩVD = 0.7 V
ID = mA
3.Medium
+−24 VR = ?4 × 2.1 V5 mA

4 yellow LEDs (forward voltage 2.1 V each) are connected in series with a resistor to a 24 V supply. Find the resistance R that sets the current to 5 mA.

Vs = 24 VVF = 2.1 Vn = 4I = 5 mA
R = Ω
4.Medium
RC​ = 4.7 kΩβ = 75VCC​ = 15 VRB​ = 1000 kΩ

An NPN transistor with β = 75 is biased by a base resistor RB = 1000 kΩ from the supply VCC = 15 V. The collector resistor is RC = 4.7 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 = 15 VRB = 1000 kΩRC = 4.7 kΩβ = 75VBE = 0.7 V
VCE = V
5.Hard
V (V)I (mA)0.65919.15Q = ?

A diode is modelled as 0.65 V in series with 25 Ω (it conducts above 0.65 V). It is in series with a 470 Ω resistor across a 9 V supply. Find the operating current ID where the diode line meets the load line.

Vs = 9 VR = 470 ΩV0 = 0.65 Vrd = 25 Ω
ID = mA
6.Hard
RC​ = 470 Ωβ = 150IC​ = ?VCC​ = 9 V5 VRB​ = 3.3 kΩ

An NPN transistor with β = 150 switches a 470 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 = 3.3 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 = 470 Ωβ = 150Vin = 5 VVBE = 0.7 VVCE(sat) = 0.2 VRB = 3.3 kΩ
IC = mA

Answer key

  1. 1. IR = 87 mA
  2. 2. ID = 8.504 mA
  3. 3. R = 3120 Ω
  4. 4. VCE = 9.959 V
  5. 5. ID = 16.87 mA
  6. 6. IC = 18.72 mA

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