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 V15 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 15 mA.

Vs = 5 VVF = 2.1 VI = 15 mA
R = Ω
2.Easy
+−Vs​6 VR = 1 kΩD1​D2​I = ?

A 6 V DC source drives current through a 1 kΩ resistor in series with two forward-biased silicon diodes. Use the constant-drop model with 0.7 V per conducting diode. Find the current I in mA.

Vs = 6 VR = 1 kΩVD = 0.7 V
I = mA
3.Medium
+−15 V470 Ω5.6 V2200 ΩIZ​ = ?

A 5.6 V Zener regulator is fed from 15 V through 470 Ω and supplies a 2200 Ω load. Find the Zener current IZ.

Vin = 15 VVZ = 5.6 VR = 470 ΩRL = 2200 Ω
IZ = mA
4.Medium
RC​ = 3.3 kΩβ = 100IC​ = ?RE​ = 1.2 kΩVCC​ = 20 VR1​ = 39 kΩR2​ = 4.7 kΩ

An NPN transistor with β = 100 has voltage-divider bias from VCC = 20 V: R₁ = 39 kΩ from VCC to the base and R₂ = 4.7 kΩ from the base to ground. The collector resistor is RC = 3.3 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 = 39 kΩR2 = 4.7 kΩRC = 3.3 kΩRE = 1.2 kΩβ = 100
IC = mA
5.Hard
+−≤ 15 V330 Ω5.1 V

A 5.1 V Zener regulator has a 330 Ω series resistor. The input can rise to 15 V, and the load may be disconnected. Find the largest power PZ,max the Zener must dissipate.

Vin,max = 15 VVZ = 5.1 VR = 330 Ω
PZ,max = mW
6.Hard
RC​ = 1 kΩβ = 150VCC​ = 9 V3.3 VRB​ = ?

An NPN transistor with β = 150 switches a 1 kΩ 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. 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 = 150Vin = 3.3 VVBE = 0.7 VVCE(sat) = 0.2 V
RB = kΩ

Answer key

  1. 1. R = 193.3 Ω
  2. 2. I = 4.6 mA
  3. 3. IZ = 17.45 mA
  4. 4. IC = 1.157 mA
  5. 5. PZ,max = 153 mW
  6. 6. RB = 44.32 kΩ

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