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 VR = ?3 V20 mA

A white LED with a forward voltage of 3 V runs from a 12 V supply through a series resistor. Find the resistance R that sets the LED current to 20 mA.

Vs = 12 VVF = 3 VI = 20 mA
R = Ω
2.Easy
+−5 VR = ?2.2 V25 mA

A green LED with a forward voltage of 2.2 V runs from a 5 V supply through a series resistor. Find the resistance R that sets the LED current to 25 mA.

Vs = 5 VVF = 2.2 VI = 25 mA
R = Ω
3.Medium
RC​ = 4.7 kΩβ = 100IC​ = ?RE​ = 1.2 kΩVCC​ = 20 VR1​ = 100 kΩR2​ = 12 kΩ

An NPN transistor with β = 100 has voltage-divider bias from VCC = 20 V: R₁ = 100 kΩ from VCC to the base and R₂ = 12 kΩ from the base to ground. The collector resistor is RC = 4.7 kΩ and the emitter resistor is RE = 1.2 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 = 100 kΩR2 = 12 kΩRC = 4.7 kΩRE = 1.2 kΩβ = 100
IC = mA
4.Medium
RC​ = 3.3 kΩβ = 75IC​ = ?VCC​ = 15 VRB​ = 470 kΩ

An NPN transistor with β = 75 is biased by a base resistor RB = 470 kΩ from the supply VCC = 15 V. The collector resistor is RC = 3.3 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 = 15 VRB = 470 kΩRC = 3.3 kΩβ = 75VBE = 0.7 V
IC = mA
5.Hard
V (V)I (mA)0.6320Q = ?

A diode is modelled as 0.6 V in series with 5 Ω (it conducts above 0.6 V). It is in series with a 150 Ω resistor across a 3 V supply. Find the operating current ID where the diode line meets the load line.

Vs = 3 VR = 150 ΩV0 = 0.6 Vrd = 5 Ω
ID = mA
6.Hard
RC​ = 1 kΩβ = 50VCC​ = 9 V5 VRB​ = ?

An NPN transistor with β = 50 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 = 50Vin = 5 VVBE = 0.7 VVCE(sat) = 0.2 V
RB = kΩ

Answer key

  1. 1. R = 450 Ω
  2. 2. R = 112 Ω
  3. 3. IC = 1.094 mA
  4. 4. IC = 2.282 mA
  5. 5. ID = 15.48 mA
  6. 6. RB = 24.43 kΩ

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