A 12 V DC source is connected through resistor R₁ = 1 kΩ to a node X. From node X to the source’s negative terminal there are two parallel paths: resistor R₂ = 2.2 kΩ, and a silicon diode with its anode at X. Use the constant-drop model with 0.7 V. Find the diode current ID in mA.
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 15 mA.
3 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 25 mA.
An NPN transistor with β = 200 has voltage-divider bias from VCC = 20 V: R₁ = 68 kΩ from VCC to the base and R₂ = 8.2 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–emitter voltage VCE.
A 6.2 V Zener regulator must supply up to 10 mA to a load. The input can drop to 12 V, and the Zener needs at least 1 mA to regulate. Find the largest series resistance Rmax that keeps it regulating.
An NPN transistor with β = 50 switches a 220 Ω load resistor connected between VCC = 5 V and its collector. The emitter is grounded. The base is driven from a 5 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.
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