EE 2115-01 - Lec 13 - 2026_09_23

Overview

Hiren Trada reviews Zener diodes as reverse-biased voltage regulators: with a series current-limiting resistor, a 4.7 V Zener can hold the output near 4.7 V once the supply exceeds its breakdown voltage, while diverting excess current. He then analyzes two 4.7 V Zeners connected back-to-back, showing how their 4.7 V breakdown plus roughly 0.7 V forward drop clips an AC waveform near +5.4 V and −5.4 V; the planned Schmitt-trigger topic is deferred.

Key takeaways

A reverse-biased 4.7 V Zener can regulate an output near 4.7 V once the supply exceeds breakdown, provided a series resistor limits current.
A Zener shunt regulator stabilizes voltage by taking more current as the supply rises; it does not inherently hold load current constant.
Two 4.7 V Zeners in series opposition clip at approximately 5.4 V because each conducting path includes one 4.7 V reverse breakdown and one roughly 0.7 V forward drop.
For a 10 V-peak AC input, back-to-back Zeners produce symmetric clipping near +5.4 V and −5.4 V.
Series-connected diode drops add, whereas parallel branches share voltage and their currents combine; analyzing each AC half-cycle identifies the forward-biased and reverse-breakdown diodes.

Chapters

0:00 Zener Diodes: Reverse-Bias Breakdown and Voltage Regulation

Zener diodes are designed to conduct in reverse bias at a specified breakdown voltage, with examples ranging from about 2 V to 200 V.
In forward bias, a Zener behaves like a conventional diode; in reverse breakdown, its voltage remains nearly constant as current changes.
The lecture’s planned Schmitt-trigger discussion is postponed because the Zener limiter review takes the class period.

3:00 A 4.7 V Zener Regulator and Its Current-Limiting Resistor

The regulator places a series resistor between supply voltage VS and the output, with the reverse-biased Zener connected across the output.
For a 4.7 V Zener, when VS is below 4.7 V the diode is off and the output follows the supply; above breakdown, the output is held near 4.7 V.
The series resistor limits current as VS rises, while the Zener shunts the excess current; the diode and resistor must remain within their current and power ratings.

11:00 Zener Shunt Current, Load Protection, and Surge Limiting

When supply voltage increases beyond the Zener rating, the Zener conducts more current to keep the output voltage near its breakdown value.
The intended benefit is protecting a load from excess voltage, but the regulator does not independently guarantee constant load current.
Trada gives surge suppression as an application and emphasizes that Zeners provide a path for excess current while clamping voltage.

14:00 Back-to-Back 4.7 V Zeners Set an AC Clipping Threshold

Two 4.7 V Zener diodes are connected in series opposition across a sinusoidal input with a 10 V peak.
On either half-cycle, one diode is forward-biased at about 0.7 V while the other enters reverse breakdown at 4.7 V, producing a clipping threshold near 5.4 V.
Because the diodes are in series, their voltage drops add; reversing the half-cycle swaps which diode is forward-biased and which is in breakdown.

24:00 Symmetric ±5.4 V Clipping and the Output Waveform

Below a magnitude of about 5.4 V, both series-opposed diodes are off and the output follows the input.
Above +5.4 V or below −5.4 V, the diodes conduct and clip the output near the corresponding threshold.
The resulting waveform has both peaks flattened; the circuit is a voltage clipper and can limit excess AC voltage, while comparator material is scheduled for a later class.

Summary, takeaways, and chapters were generated by AI from the video's transcript and may contain errors. The video belongs to its creator, Hiren Trada.