Question

i want to take a 12vac input voltage and convert it to 20vdc , 12vdc+, 12vdc-, 5vdc+

How can i do that using a full bridge rectifier, zener diodes, diodes, capacitors. Cannot use a voltage rectifier chip.

Answer 1

Things you need

1. 230/20v and 230/12v and 230/5v transformer (use one transformer according to output )
2. 7812
3. IN4001 (4)
4. Capacitor 1000uF
5. Dot board/ bread board/ PCB board.
6. Connecting wires (As required)
7. Power chord

Circuit Diagram

Steps to do

• First connect primary side of transformer with free end of power chord.
  • to identify which side is primary follow either any one of these steps
    • Always red colour wire end will be primary and black colour wire end will be secondary.
    • if you have multi meter check the resistance, primary side will have higher resistance and secondary will have lower resistance (Sometimes you may not notice the difference as you might be using transformer for smaller size)
    • or else if possible supply lower AC voltage on either side and check the output on other side. By that you can identify which side is stepping down.
  • DO NOT forget to cover the joints with insulation tape, as this going to interface directly with 230V AC.
• connect secondary sides to bread board (or to which ever you using).
• Arrange the IN4001 as shown in figure.
  • The cathode (n) is identified by a bar on diode case. The other terminal is the anode (p)

• connect the capacitor across two wire outs from didoe.
• connect the wire out from diode after capacitor to 7812.
  • it has three pins, in, gnd, out.

• Take the wire from out and gnd from 7812 and use wherever you want.
• That has voltage 12V and amp rating of which ever transformer you used.
• if we want -12 v than change the output terminal.
• we want 20 v than use 230/20 v transformer.
• if we want 5 v than use 230/5 v transformer.