--- title: "Unregulated dc supply with bridge rectifier" subject: "Electronics Devices and Circuit" chapter: 6 key: "semester_3/electronics_devices_and_circuit:unregulated-bridge-power-supply" source: https://www.bctengineer.com/q/semester_3/electronics_devices_and_circuit/unregulated-bridge-power-supply site: BCT Engineering --- # Unregulated dc supply with bridge rectifier Electronics Devices and Circuit · Chapter 6: Power Supplies, Breakdown Diodes, and Voltage Regulators - Asked in: 2072 Kartik, 2 marks - Video: [Design of Unregulated DC Power Supply (Basics Electronics) BE/Btech 1st year](https://www.youtube.com/watch?v=dc2U_gjV81A) — Gautam Varde - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_3/electronics_devices_and_circuit/unregulated-bridge-power-supply - Whole chapter: https://www.bctengineer.com/md/semester_3/electronics_devices_and_circuit/chapter-6 ## Question Draw unregulated dc voltage power supply using bridge rectifier. ## Short answer A step-down transformer reduces mains AC. A bridge rectifier of four diodes converts it to full-wave pulsating DC. A filter capacitor smooths the output to an unregulated DC voltage: Vdc ≈ Vm - 1.4 V, with peak-to-peak ripple Vr(p-p) ≈ IL/(2fC). ## Answer ```text 230 V ac +---------+ +---------+ +--------+ mains o--->| Step- |--->| Bridge |-->| Filter |--> unregulated | down | | rectif. | | C | dc output | T/F | |(4 diode)| +--------+ to load +---------+ +---------+ ``` Circuit: ```text T1 D1 D2 230 V o--+ +--A--+---|>|---+---|<|---+--B--+ ac ) || ( | | | | mains ) || ( | (+) | | ) || ( | | | o--+ +--+ | (−) | | | | | | | | +---|<|---+---|>|---+ | | D3 D4 | +----------------------------+ Filter and load, connected to the bridge output: (+) o----+--------+----o +Vdc (unregulated) | | [C] [RL] | | (−) o----+--------+----o GND ``` - A step-down transformer reduces the 230 V mains to the required ac voltage. - The bridge rectifier (four diodes D1 to D4) converts the ac to pulsating dc (full-wave): D1 and D4 conduct in one half-cycle, and D2 and D3 in the other. - A filter capacitor C charges to the peak and discharges through the load between peaks, smoothing the output. Ripple voltage: Vr(p-p) ≈ IL/(2fC). - The output Vdc ≈ Vm − 1.4 V is unregulated: it changes when the mains voltage or the load changes. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is the correct order of blocks in an unregulated bridge power supply? A. Bridge rectifier, transformer, filter, load B. Step-down transformer, bridge rectifier, filter capacitor, load C. Filter, bridge rectifier, transformer, load D. Transformer, filter, bridge rectifier, load Answer: B. The transformer lowers the mains first, the rectifier makes pulsating dc and the filter smooths it. (Key point: Block order) 2. What does the filter capacitor do? A. Charges to the peak and discharges through the load between peaks, reducing ripple B. Converts ac to dc C. Steps the voltage down D. Holds the output voltage constant for any mains change Answer: A. The output is still unregulated; ripple is Vr(p-p) ≈ IL/(2fC). (Key point: Role of filter) 3. Why is the output called unregulated, and what is Vdc approximately? A. It is constant; Vdc ≈ Vm + 1.4 V B. It is constant; Vdc ≈ Vm - 0.7 V C. It varies with mains and load; Vdc ≈ Vm - 1.4 V D. It varies only with temperature; Vdc ≈ Vm/2 Answer: C. Two diodes conduct in each half-cycle, giving 1.4 V drop, and nothing stabilises the output. 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