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​15 VR = 3.3 kΩD1​D2​I = ?

A 15 V DC source drives current through a 3.3 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 = 15 VR = 3.3 kΩVD = 0.7 V
I = mA
2.Easy
+−24 VR = ?3 V20 mA

A white LED with a forward voltage of 3 V runs from a 24 V supply through a series resistor. Find the resistance R that sets the LED current to 20 mA.

Vs = 24 VVF = 3 VI = 20 mA
R = Ω
3.Medium
+−24 VR = ?3 × 3.2 V5 mA

3 blue LEDs (forward voltage 3.2 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 = 3.2 Vn = 3I = 5 mA
R = Ω
4.Medium
RC​ = 470 Ωβ = 120VCC​ = 9 VRB​ = 270 kΩ

An NPN transistor with β = 120 is biased by a base resistor RB = 270 kΩ from the supply VCC = 9 V. The collector resistor is RC = 470 Ω and the emitter is grounded. Take VBE = 0.7 V and assume the transistor is in the active region. Find the collector–emitter voltage VCE.

VCC = 9 VRB = 270 kΩRC = 470 Ωβ = 120VBE = 0.7 V
VCE = V
5.Hard
RC​ = 680 Ωβ = 50VCC​ = 9 V3.3 VRB​ = ?

An NPN transistor with β = 50 switches a 680 Ω 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 = 680 Ωβ = 50Vin = 3.3 VVBE = 0.7 VVCE(sat) = 0.2 V
RB = kΩ
6.Hard
RC​ = 1 kΩβ = 100IC​ = ?VCC​ = 12 V5 VRB​ = 220 kΩ

An NPN transistor with β = 100 switches a 1 kΩ load resistor connected between VCC = 12 V and its collector. The emitter is grounded. The base is driven from a 5 V logic output through a base resistor RB = 220 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 = 12 VRC = 1 kΩβ = 100Vin = 5 VVBE = 0.7 VVCE(sat) = 0.2 VRB = 220 kΩ
IC = mA

Answer key

  1. 1. I = 4.121 mA
  2. 2. R = 1050 Ω
  3. 3. R = 2880 Ω
  4. 4. VCE = 7.266 V
  5. 5. RB = 10.05 kΩ
  6. 6. IC = 1.955 mA

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