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
+−Vs​3 VR = 1 kΩD​I = ?

A 3 V DC source drives current through a 1 kΩ resistor in series with a forward-biased silicon diode. Use the constant-drop model with 0.7 V per conducting diode. Find the current I in mA.

Vs = 3 VR = 1 kΩVD = 0.7 V
I = mA
2.Easy
+−5 VR = ?3.2 V20 mA

A blue LED with a forward voltage of 3.2 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 = 3.2 VI = 20 mA
R = Ω
3.Medium
+−15 V150 Ω9.1 V2200 ΩIZ​ = ?

A 9.1 V Zener regulator is fed from 15 V through 150 Ω and supplies a 2200 Ω load. Find the Zener current IZ.

Vin = 15 VVZ = 9.1 VR = 150 ΩRL = 2200 Ω
IZ = mA
4.Medium
+−12 VR = ?2 × 3 V5 mA

2 white LEDs (forward voltage 3 V each) are connected in series with a resistor to a 12 V supply. Find the resistance R that sets the current to 5 mA.

Vs = 12 VVF = 3 Vn = 2I = 5 mA
R = Ω
5.Hard
V (V)I (mA)0.666Q = ?

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 1000 Ω resistor across a 6 V supply. Find the operating current ID where the diode line meets the load line.

Vs = 6 VR = 1000 ΩV0 = 0.6 Vrd = 20 Ω
ID = mA
6.Hard
RC​ = 680 Ωβ = 200IC​ = ?VCC​ = 5 V3.3 VRB​ = 1 kΩ

An NPN transistor with β = 200 switches a 680 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 = 1 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 = 5 VRC = 680 Ωβ = 200Vin = 3.3 VVBE = 0.7 VVCE(sat) = 0.2 VRB = 1 kΩ
IC = mA

Answer key

  1. 1. I = 2.3 mA
  2. 2. R = 90 Ω
  3. 3. IZ = 35.2 mA
  4. 4. R = 1200 Ω
  5. 5. ID = 5.294 mA
  6. 6. IC = 7.059 mA

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