Transformer, Bridge Rectifier and 7805 Power Supply: Circuit, Measurements and Online Simulator

To build this Transformer, Bridge Rectifier and 7805 Power Supply circuit you need a 230 V 50 hz mains supply, a 230 V to 12 V transformer, four 1N4007 diodes, a 1000 µF electrolytic capacitor, a 5 V regulator (78xx), a 330 Ω resistor, a green LED, an oscilloscope and a digital multimeter. 230 V mains through a 12 V transformer, a four-diode bridge, a 1000 µF reservoir capacitor and a 7805 regulator: a real 5 V supply, with the ripple on the scope. Make the 20 connections in the wiring table, press Run, and cH1 is the transformer AC, CH2 the rectified, smoothed DC (about 15 V); the multimeter reads the regulated 5 V. Change C to 100 µ to watch the ripple grow while the 7805 still holds 5 V.

Open this circuit in the free Electronics bench simulator

Parts list

QtyPartWhat it does
1230 V 50 Hz mains supplyWall AC: 230 V 50 Hz (India, Europe) or 120 V 60 Hz (US), RMS. Never touch it directly in real life — step it down with a transformer first. The neutral is earthed.
1230 V to 12 V transformerSteps AC voltage by the turns ratio: 230 V in, 12 V out (RMS). The secondary is isolated; CT is its centre tap (half the voltage each side) for a two-diode full-wave rectifier.
41N4007 diodeConducts from A (anode) to K (cathode, the striped end) once about 0.7 V is across it; blocks the other way.
11000 µF electrolytic capacitorA large, polarised capacitor for smoothing supplies: the stripe marks − . Reverse it, or exceed its voltage rating, and it fails.
15 V regulator (78xx)Turns a higher, rough DC into a steady one: IN needs about 2 V more than OUT. Add 0.33 µF on IN and 0.1 µF on OUT.
1330 Ω resistorLimits current. 220 Ω in series with an LED; 10 kΩ as a pull-up or pull-down.
1green LEDLights when A (anode, the bent leg) is high and C (cathode) is low. Use a resistor.
1OscilloscopeTwo channels against earth (GND). Turn TIME/DIV and VOLTS/DIV to fit the wave, set the trigger level to steady it, and read Vpp, RMS and frequency. X-Y mode draws Lissajous figures. Choose a digital (DSO) or phosphor (CRO) screen.
1Digital MultimeterTurn the dial: V (across a part, COM and V), A (in series, COM and A), Ω / continuity / diode (on an unpowered part), Hz. The A range has a 10 A fuse — put it across a supply and it blows.

Wiring

#FromTo
1230 V 50 Hz mains supply L230 V to 12 V transformer P1
2230 V 50 Hz mains supply N230 V to 12 V transformer P2
3230 V to 12 V transformer S11N4007 diode (d1) A
4230 V to 12 V transformer S21N4007 diode (d2) A
51N4007 diode (d1) K1000 µF electrolytic capacitor +
61N4007 diode (d2) K1000 µF electrolytic capacitor +
71N4007 diode (d3) K230 V to 12 V transformer S1
81N4007 diode (d4) K230 V to 12 V transformer S2
91N4007 diode (d3) A1000 µF electrolytic capacitor -
101N4007 diode (d4) A1000 µF electrolytic capacitor -
111000 µF electrolytic capacitor +5 V regulator (78xx) IN
125 V regulator (78xx) GND1000 µF electrolytic capacitor -
135 V regulator (78xx) OUT330 Ω resistor leg 1
14330 Ω resistor leg 2green LED anode (A, long leg)
15green LED cathode (C, short leg)1000 µF electrolytic capacitor -
161000 µF electrolytic capacitor -Oscilloscope GND
17230 V to 12 V transformer S1Oscilloscope CH1
181000 µF electrolytic capacitor +Oscilloscope CH2
195 V regulator (78xx) OUTDigital Multimeter V
201000 µF electrolytic capacitor -Digital Multimeter COM

Step by step

  1. Open the electronics bench. Open the BitForBytes Embedded Lab in your browser. A circuit with no microcontroller runs on the analog bench: no install or account is needed.
  2. Add the parts. Add a 230 V 50 hz mains supply, a 230 V to 12 V transformer, four 1N4007 diodes, a 1000 µF electrolytic capacitor, a 5 V regulator (78xx), a 330 Ω resistor, a green LED, an oscilloscope and a digital multimeter from the parts palette (Instruments, Power, Passive and Semiconductors).
  3. Wire 1. Connect 230 V 50 Hz mains supply L to 230 V to 12 V transformer P1.
  4. Wire 2. Connect 230 V 50 Hz mains supply N to 230 V to 12 V transformer P2.
  5. Wire 3. Connect 230 V to 12 V transformer S1 to 1N4007 diode (d1) A.
  6. Wire 4. Connect 230 V to 12 V transformer S2 to 1N4007 diode (d2) A.
  7. Wire 5. Connect 1N4007 diode (d1) K to 1000 µF electrolytic capacitor +.
  8. Wire 6. Connect 1N4007 diode (d2) K to 1000 µF electrolytic capacitor +.
  9. Wire 7. Connect 1N4007 diode (d3) K to 230 V to 12 V transformer S1.
  10. Wire 8. Connect 1N4007 diode (d4) K to 230 V to 12 V transformer S2.
  11. Wire 9. Connect 1N4007 diode (d3) A to 1000 µF electrolytic capacitor -.
  12. Wire 10. Connect 1N4007 diode (d4) A to 1000 µF electrolytic capacitor -.
  13. Wire 11. Connect 1000 µF electrolytic capacitor + to 5 V regulator (78xx) IN.
  14. Wire 12. Connect 5 V regulator (78xx) GND to 1000 µF electrolytic capacitor -.
  15. Wire 13. Connect 5 V regulator (78xx) OUT to 330 Ω resistor leg 1.
  16. Wire 14. Connect 330 Ω resistor leg 2 to green LED anode (A, long leg).
  17. Wire 15. Connect green LED cathode (C, short leg) to 1000 µF electrolytic capacitor -.
  18. Wire 16. Connect 1000 µF electrolytic capacitor - to Oscilloscope GND.
  19. Wire 17. Connect 230 V to 12 V transformer S1 to Oscilloscope CH1.
  20. Wire 18. Connect 1000 µF electrolytic capacitor + to Oscilloscope CH2.
  21. Wire 19. Connect 5 V regulator (78xx) OUT to Digital Multimeter V.
  22. Wire 20. Connect 1000 µF electrolytic capacitor - to Digital Multimeter COM.
  23. Run and measure. Press Run. CH1 is the transformer AC, CH2 the rectified, smoothed DC (about 15 V); the multimeter reads the regulated 5 V. Change C to 100 µ to watch the ripple grow while the 7805 still holds 5 V.

Lab sheet

// Electronics bench: a linear power supply from the wall
//
// 1. Transformer: 230 V to 12 V RMS (about 17 V peak), isolated from the mains.
// 2. Bridge rectifier: four diodes turn both halves of the AC positive (two diode drops, about 1.4 V).
// 3. Reservoir capacitor: holds the peak (about 15.5 V) between the 100 Hz charging pulses.
// 4. 7805: drops whatever is left to a steady 5.00 V (it needs about 2 V of headroom).
//
// Ripple = I / (2 · f · C): more current, or a smaller C, means more ripple.

What to try

Press Run. CH1 is the transformer AC, CH2 the rectified, smoothed DC (about 15 V); the multimeter reads the regulated 5 V. Change C to 100 µ to watch the ripple grow while the 7805 still holds 5 V.

Frequently asked questions

How do I wire the Transformer, Bridge Rectifier and 7805 Power Supply circuit?

Make 20 connections: 230 V 50 Hz mains supply L to 230 V to 12 V transformer P1; 230 V 50 Hz mains supply N to 230 V to 12 V transformer P2; 230 V to 12 V transformer S1 to 1N4007 diode (d1) A; 230 V to 12 V transformer S2 to 1N4007 diode (d2) A; 1N4007 diode (d1) K to 1000 µF electrolytic capacitor +; 1N4007 diode (d2) K to 1000 µF electrolytic capacitor +; 1N4007 diode (d3) K to 230 V to 12 V transformer S1; 1N4007 diode (d4) K to 230 V to 12 V transformer S2; 1N4007 diode (d3) A to 1000 µF electrolytic capacitor -; 1N4007 diode (d4) A to 1000 µF electrolytic capacitor -; 1000 µF electrolytic capacitor + to 5 V regulator (78xx) IN; 5 V regulator (78xx) GND to 1000 µF electrolytic capacitor -; 5 V regulator (78xx) OUT to 330 Ω resistor leg 1; 330 Ω resistor leg 2 to green LED anode (A, long leg); green LED cathode (C, short leg) to 1000 µF electrolytic capacitor -; 1000 µF electrolytic capacitor - to Oscilloscope GND; 230 V to 12 V transformer S1 to Oscilloscope CH1; 1000 µF electrolytic capacitor + to Oscilloscope CH2; 5 V regulator (78xx) OUT to Digital Multimeter V; 1000 µF electrolytic capacitor - to Digital Multimeter COM.

What parts do I need for the Transformer, Bridge Rectifier and 7805 Power Supply?

A 230 V 50 hz mains supply, a 230 V to 12 V transformer, four 1N4007 diodes, a 1000 µF electrolytic capacitor, a 5 V regulator (78xx), a 330 Ω resistor, a green LED, an oscilloscope and a digital multimeter.

Can I simulate the Transformer, Bridge Rectifier and 7805 Power Supply online for free?

Yes. The BitForBytes Embedded Lab solves the circuit in time, the way SPICE does (nodal analysis with real diode, transistor and capacitor models), and gives you a bench power supply, function generator, oscilloscope and multimeter to measure it — free, in the browser.

What does this circuit show?

230 V mains through a 12 V transformer, a four-diode bridge, a 1000 µF reservoir capacitor and a 7805 regulator: a real 5 V supply, with the ripple on the scope.

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