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Short note: Regulated power supply

Short answer

A regulated power supply maintains constant DC output despite input or load variations, typically using a transformer, rectifier, filter capacitor and a three-terminal IC regulator like 7805. The IC provides fixed voltage (e.g., +5V) with built-in current limiting and thermal protection, simplifying design.

Write a short note on regulated power supply (using IC).

A regulated power supply gives a constant DC output voltage even when the AC input voltage or the load current varies. An IC regulator (a fixed three-terminal 78xx for positive or 79xx for negative output) is the simplest way to do this.

Block diagram

 AC --[Transformer]--[Rectifier]--[Filter C]--[IC 7805]-- DC out
 mains  (step down)  (bridge)     (smoothing)  regulator   +5 V

Circuit with IC 7805

             +-----------------+
 Vin ---+----| IN   7805   OUT |----+--------+---- Vout = +5 V
 (7-25V)|    +--------+--------+    |        |
        C1           GND            C2      Load
     0.33uF           |           0.1uF      |
        |             |             |        |
 -------+-------------+-------------+--------+---- GND
  • The transformer steps the 220 V mains down to a lower AC voltage.
  • The bridge rectifier converts AC to pulsating DC, and the capacitor filter smooths it.
  • The 7805 holds the output at a steady 5 V as long as the input is at least 2 to 3 V above the output (about 7 to 25 V).
  • C1 and C2 improve stability and remove high-frequency noise.

The 78xx series gives fixed outputs such as 5, 6, 8, 9, 12, 15 and 24 V, at up to 1 A. The LM317 gives an adjustable output. Advantages: simple, cheap, with built-in current limiting and thermal shutdown.

✓ Answer checked by Claude Opus 5.5 (high effort)

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