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
+−9 VR = ?2.1 V5 mA

A yellow LED with a forward voltage of 2.1 V runs from a 9 V supply through a series resistor. Find the resistance R that sets the LED current to 5 mA.

Vs = 9 VVF = 2.1 VI = 5 mA
R = Ω
2.Easy
+−Vs​24 VR = 1 kΩD​I = ?

A 24 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 = 24 VR = 1 kΩVD = 0.7 V
I = mA
3.Medium
+−9 V270 Ω5.1 V3300 ΩIZ​ = ?

A 5.1 V Zener regulator is fed from 9 V through 270 Ω and supplies a 3300 Ω load. Find the Zener current IZ.

Vin = 9 VVZ = 5.1 VR = 270 ΩRL = 3300 Ω
IZ = mA
4.Medium
RC​ = 2.2 kΩβ = 120RE​ = 1.5 kΩVCC​ = 18 VR1​ = 39 kΩR2​ = 12 kΩ

An NPN transistor with β = 120 has voltage-divider bias from VCC = 18 V: R₁ = 39 kΩ from VCC to the base and R₂ = 12 kΩ from the base to ground. The collector resistor is RC = 2.2 kΩ and the emitter resistor is RE = 1.5 kΩ. Take VBE = 0.7 V and use the Thévenin equivalent of the divider (do not neglect the base current). Find the collector–emitter voltage VCE.

VCC = 18 VR1 = 39 kΩR2 = 12 kΩRC = 2.2 kΩRE = 1.5 kΩβ = 120
VCE = V
5.Hard
RC​ = 330 Ωβ = 100IC​ = ?VCC​ = 9 V3.3 VRB​ = 22 kΩ

An NPN transistor with β = 100 switches a 330 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 = 22 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 = 9 VRC = 330 Ωβ = 100Vin = 3.3 VVBE = 0.7 VVCE(sat) = 0.2 VRB = 22 kΩ
IC = mA
6.Hard
RC​ = 100 Ωβ = 50VCC​ = 5 V3.3 VRB​ = ?

An NPN transistor with β = 50 switches a 100 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 = 100 Ωβ = 50Vin = 3.3 VVBE = 0.7 VVCE(sat) = 0.2 V
RB = kΩ

Answer key

  1. 1. R = 1380 Ω
  2. 2. I = 23.3 mA
  3. 3. IZ = 12.9 mA
  4. 4. VCE = 9.74 V
  5. 5. IC = 11.82 mA
  6. 6. RB = 2.708 kΩ

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