--- title: "Choppers; single-phase full bridge inverter" subject: "Advanced Electronics" chapter: 7 key: "semester_4/advanced_electronics:choppers-full-bridge-inverter" source: https://www.bctengineer.com/q/semester_4/advanced_electronics/choppers-full-bridge-inverter site: BCT Engineering --- # Choppers; single-phase full bridge inverter Advanced Electronics · Chapter 7: Introduction to Power Electronics - Asked in: 2071 Chaitra, 2+5 marks; 2069 Chaitra, 2+5 marks (asked 2 times) - Video: [Single Phase Full Bridge Inverter (Basics, Circuit, Working, Waveforms & Applications) Explained](https://www.youtube.com/watch?v=-WU3BxOxvII) — Engineering Funda - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_4/advanced_electronics/choppers-full-bridge-inverter - Whole chapter: https://www.bctengineer.com/md/semester_4/advanced_electronics/chapter-7 ## Question What are choppers? Explain the working principle of single phase, full bridge inverter with necessary circuits and waveforms. ## Short answer Choppers are DC-DC converters that vary average output by high-frequency switching (Vo = k·Vs). A single-phase full-bridge inverter uses four switches (S1–S4); alternately firing S1&S2 and S3&S4 produces a ±Vs square wave across the load. RMS output is Vs, fundamental component is 0.9Vs, and antiparallel diodes handle reactive energy. ## Answer #### Choppers A **chopper** is a static DC-to-DC converter that converts a fixed DC voltage into a variable DC voltage by switching a semiconductor device ON and OFF at high frequency. The average output is Vo = k·Vs (step-down), where k = Ton/T is the duty cycle. Choppers are used in DC motor drives, battery vehicles and SMPS. #### Single-phase full-bridge inverter A full-bridge inverter uses four switches (S1–S4, SCRs/IGBTs with antiparallel diodes D1–D4) and one DC source Vs to produce an AC square wave of ±Vs across the load. ```text +Vs +---+-----------+ | | | | S1 D1 S3 D3 | | LOAD | | A---[ R ]---B | | | | S4 D4 S2 D2 | | | +---+-----------+ 0 (−) ``` **Working:** 1. **0 < t < T/2:** S1 and S2 are ON. Current flows +Vs → S1 → A → load → B → S2 → negative. vAB = +Vs. 2. **T/2 < t < T:** S3 and S4 are ON. Current flows +Vs → S3 → B → load → A → S4 → negative. vAB = −Vs. 3. Switches in the same leg (S1–S4 or S3–S2) are never ON together, or the supply would be short-circuited. 4. With an **RL load**, current lags; when switches change over, the stored energy returns to the source through the diodes (D3, D4 or D1, D2) before the current reverses. These are **feedback diodes**. **Waveforms (resistive load):** ```text gate S1,S2 |‾‾‾‾‾|_____|‾‾‾‾‾|_____ gate S3,S4 |_____|‾‾‾‾‾|_____|‾‾‾‾‾ 0 T/2 T vo +Vs +-----+ +-----+ | | | | 0 ---+-----+-----+-----+---> t | | | | −Vs +-----+ +--- ``` **Output relations:** - Output is a square wave of amplitude Vs (twice that of a half-bridge with the same supply). - RMS output voltage Vo = Vs. - Fourier series: vo = Σ (4Vs/nπ) sin nωt for n = 1, 3, 5, …; fundamental RMS = 4Vs/(√2·π) = 0.9·Vs. - Frequency is set by the switching rate; output voltage can be varied by PWM. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is a chopper? A. An AC-to-DC rectifier B. A DC-to-DC converter that gives variable DC from fixed DC by switching ON and OFF C. A DC-to-AC converter D. An AC voltage regulator Answer: B. A chopper switches a device at high frequency; Vo = k·Vs for step-down. (Key point: Chopper definition) 2. In a full-bridge inverter, which switches conduct in the first half cycle to give +Vs? A. S1 and S4 B. S3 and S4 C. S1 and S2 D. All four switches Answer: C. S1 and S2 ON gives vAB = +Vs; S3 and S4 ON gives −Vs. (Key point: Conducting switches) 3. Why must S1 and S4 (same leg) never be ON together? A. It would reverse the load current twice B. It would double the output frequency C. It would turn off the feedback diodes D. It would short-circuit the DC supply Answer: D. Both switches in one leg conducting directly connects +Vs to ground. (Key point: Same-leg rule) 4. What is the role of feedback diodes with an RL load? A. Return stored inductive energy to the source while the current is still lagging B. Block the reverse supply voltage C. Increase the output frequency D. Limit the supply voltage to Vs/2 Answer: A. After switching, load current continues through the diodes before reversing. (Key point: Feedback diodes) ## Related in Advanced Electronics - [Chopper definition; single-phase half bridge inverter](https://www.bctengineer.com/question.md?key=semester_4%2Fadvanced_electronics%3Achopper-half-bridge-inverter) — Advanced Electronics, chapter 7 - [Full bridge inverter; dc-dc output power control](https://www.bctengineer.com/question.md?key=semester_4%2Fadvanced_electronics%3Afull-bridge-inverter-dc-dc-control) — Advanced Electronics, chapter 7 - [Boost regulator working principle](https://www.bctengineer.com/question.md?key=semester_4%2Fadvanced_electronics%3Aboost-regulator-principle) — Advanced Electronics, chapter 8, asked 2× - [Variable inverter output; SCR full-wave average](https://www.bctengineer.com/question.md?key=semester_4%2Fadvanced_electronics%3Ainverter-variable-output-scr-fwr) — Advanced Electronics, chapter 7 ## Related in other subjects - [Single-phase full-wave inverter with 5 Ω load](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_electronics%3Afull-wave-inverter-5ohm) — Power Electronics, chapter 5 - [Three-phase bridge inverter, 120° conduction](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_electronics%3Athree-phase-inverter-120-conduction) — Power Electronics, chapter 5 - [Full-bridge inverter RLC load to fifth harmonic](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_electronics%3Afull-bridge-inverter-rlc-155uf) — Power Electronics, chapter 5 - [Full-bridge inverter RLC load, THD](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_electronics%3Afull-bridge-inverter-rlc-112uf) — Power Electronics, chapter 5