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
+−24 VR = ?3.2 V15 mA

A blue LED with a forward voltage of 3.2 V runs from a 24 V supply through a series resistor. Find the resistance R that sets the LED current to 15 mA.

Vs = 24 VVF = 3.2 VI = 15 mA
R = Ω
2.Easy
+−15 V100 Ω6.2 VIR​ = ?

A 6.2 V Zener diode is fed from 15 V through a 100 Ω resistor, with no load connected. Find the current IR in the resistor.

Vin = 15 VVZ = 6.2 VR = 100 Ω
IR = mA
3.Medium
+−24 VR = ?2 × 2 V5 mA

2 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 5 mA.

Vs = 24 VVF = 2 Vn = 2I = 5 mA
R = Ω
4.Medium
RC​ = 4.7 kΩβ = 120IC​ = ?VCC​ = 9 VRB​ = 820 kΩ

An NPN transistor with β = 120 is biased by a base resistor RB = 820 kΩ from the supply VCC = 9 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 current IC in mA.

VCC = 9 VRB = 820 kΩRC = 4.7 kΩβ = 120VBE = 0.7 V
IC = mA
5.Hard
+−≤ 19 V680 Ω5.1 V

A 5.1 V Zener regulator has a 680 Ω series resistor. The input can rise to 19 V, and the load may be disconnected. Find the largest power PZ,max the Zener must dissipate.

Vin,max = 19 VVZ = 5.1 VR = 680 Ω
PZ,max = mW
6.Hard
RC​ = 100 Ωβ = 100VCC​ = 24 V3.3 VRB​ = ?

An NPN transistor with β = 100 switches a 100 Ω load resistor connected between VCC = 24 V and its collector. The emitter is grounded. The base is driven from a 3.3 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 = 24 VRC = 100 Ωβ = 100Vin = 3.3 VVBE = 0.7 VVCE(sat) = 0.2 V
RB = kΩ

Answer key

  1. 1. R = 1387 Ω
  2. 2. IR = 88 mA
  3. 3. R = 4000 Ω
  4. 4. IC = 1.215 mA
  5. 5. PZ,max = 104.3 mW
  6. 6. RB = 1.092 kΩ

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