[ AETN2201 ] Midterm Question Review

• By Ohm's law, increasing the series resistance reduces the circuit current, which lowers the forward current through the diode and decreases its brightness. Conversely, decreasing the resistance increases the current, making the LED brighter.

Fully explain what happens to the diode current and LED brightness when the resistor is varied

• Reduces voltage ripple by storing electrical energy during voltage peaks and discharging it through the load during voltage dips.

• This "fills in the valleys" of the pulsating waveform, which significantly raises the average DC output voltagecloser to the peak AC value.

What’s the effect of adding a smoothing capacitor to a full wave rectifier?

• Voltage Diode Test (Forward/Reverse Voltage)

• Ohmmeter Diode Test (Forward/Reverse Bias)

What test do you use to test the condition of the diode?

• The circuit regulates because the Zener diode operates in its reverse breakdown region. 

• As long as the resistor values keep the voltage across the diode equal to or greater than the Zener breakdown voltage, it maintains a stable, constant output voltage despite fluctuations.

• Zener continues to regulate as long as the Zener current remains above its minimum knee threshold.

Why does a Zener diode regulate?

• Depending on the load demand (IL = Vz / R), the circuit won’t be able to supply the current it needs because the series resistor would limit the total current.

Describe what would happen if you put a RLOAD of 1Ω across your Zener diode.

• It prevents excessive current from flowing through the Zener diode, protecting it from overheating and burning out.

What is the Series Resistor for?

• The input waveform (Es) gets clipped or "flat-topped" because the 33uF capacitor draws massive current spikes during the peaks of the AC cycle to charge rapidly

What is the effect of adding a capacitor to the circuit?

A half-wave rectifier converts only one half-cycle of an AC input signal into pulsating DC using a single diode, whereas a full-wave rectifier converts the entire AC cycle into pulsating DC using two or four diodes

Difference between Half-Wave and Full-Wave Rectifier

• When a regular (conventional) diode enters the reverse-breakdown region, it experiences a sharp, uncontrolled spike in reverse current, which typically overheats and permanently destroys the device

What happens to a regular diode when it enters breakdown region?

• A half-wave rectifier is inefficient because its maximum theoretical conversion efficiency is only 40.6% and it blocks half of every AC input cycle, meaning a large portion of the supplied energy goes unused.

• The circuit conducts current during only one-half of the AC wave (positive or negative) and blocks the other half entirely. This leaves 50% of the input time domain completely unused for power delivery.

Why is a half-wave rectifier considered inefficient?