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
+−5 VR = ?2.1 V20 mA

A yellow LED with a forward voltage of 2.1 V runs from a 5 V supply through a series resistor. Find the resistance R that sets the LED current to 20 mA.

Vs = 5 VVF = 2.1 VI = 20 mA
R = Ω
2.Easy
+−Vs​12 VR1​ = 1 kΩR2​ = 470 ΩID​ = ?

A 12 V DC source is connected through resistor R₁ = 1 kΩ to a node X. From node X to the source’s negative terminal there are two parallel paths: resistor R₂ = 470 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 = 12 VR1 = 1 kΩR2 = 470 ΩVD = 0.7 V
ID = mA
3.Medium
RC​ = 1.2 kΩβ = 80IC​ = ?VCC​ = 15 VRB​ = 150 kΩ

An NPN transistor with β = 80 is biased by a base resistor RB = 150 kΩ from the supply VCC = 15 V. The collector resistor is RC = 1.2 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 = 150 kΩRC = 1.2 kΩβ = 80VBE = 0.7 V
IC = mA
4.Medium
RC​ = 1.5 kΩβ = 150IC​ = ?VCC​ = 12 VRB​ = 390 kΩ

An NPN transistor with β = 150 is biased by a base resistor RB = 390 kΩ from the supply VCC = 12 V. The collector resistor is RC = 1.5 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 = 12 VRB = 390 kΩRC = 1.5 kΩβ = 150VBE = 0.7 V
IC = mA
5.Hard
V (V)I (mA)0.6627.27Q = ?

A diode is modelled as 0.6 V in series with 20 Ω (it conducts above 0.6 V). It is in series with a 220 Ω resistor across a 6 V supply. Find the operating current ID where the diode line meets the load line.

Vs = 6 VR = 220 ΩV0 = 0.6 Vrd = 20 Ω
ID = mA
6.Hard
RC​ = 150 Ωβ = 100VCC​ = 5 V3.3 VRB​ = ?

An NPN transistor with β = 100 switches a 150 Ω load resistor connected between VCC = 5 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 = 5 VRC = 150 Ωβ = 100Vin = 3.3 VVBE = 0.7 VVCE(sat) = 0.2 V
RB = kΩ

Answer key

  1. 1. R = 145 Ω
  2. 2. ID = 9.811 mA
  3. 3. IC = 7.627 mA
  4. 4. IC = 4.346 mA
  5. 5. ID = 22.5 mA
  6. 6. RB = 8.125 kΩ

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