Diodes & transistors worksheet with answers

A blue LED with a forward voltage of 3.2 V runs from a 12 V supply through a series resistor. Find the resistance R that sets the LED current to 5 mA.

A 10 V DC source is connected through resistor R₁ = 330 Ω to a node X. From node X to the source’s negative terminal there are two parallel paths: resistor R₂ = 680 Ω, and a silicon diode with its anode at X. Use the constant-drop model with 0.7 V. Find the diode current I_D in mA.

An NPN transistor with β = 80 has voltage-divider bias from V_CC = 12 V: R₁ = 39 kΩ from V_CC to the base and R₂ = 8.2 kΩ from the base to ground. The collector resistor is R_C = 2.2 kΩ and the emitter resistor is R_E = 1 kΩ. Take V_BE = 0.7 V and use the Thévenin equivalent of the divider (do not neglect the base current). Find the collector current I_C in mA.

An NPN transistor with β = 120 is biased by a base resistor R_B = 270 kΩ from the supply V_CC = 9 V. The collector resistor is R_C = 470 Ω and the emitter is grounded. Take V_BE = 0.7 V and assume the transistor is in the active region. Find the collector–emitter voltage V_CE.

A diode is modelled as 0.65 V in series with 5 Ω (it conducts above 0.65 V). It is in series with a 150 Ω resistor across a 6 V supply. Find the operating current I_D where the diode line meets the load line.

An NPN transistor with β = 150 switches a 330 Ω load resistor connected between V_CC = 12 V and its collector. The emitter is grounded. The base is driven from a 5 V logic output through a base resistor R_B. Take V_BE = 0.7 V and V_CE(sat) = 0.2 V. Find the largest base resistor R_B, in kΩ, that still drives the transistor just into saturation.