How do I convert a 240V AC to 12V DC?
Well there are many ways in converting 240 V AC supply to DC supply. Simple method would be using a Full - Wave Rectifier. A Full-wave rectifier is a circuit designed to convert AC supply to DC supply using diodes , then filtered using capacitor to eliminate the noise in the circuit.
this is a simple diagram of how a convertor works. You can eliminate the capacitor and LM2904 if needed as they are purely used in this circuit to eliminate noise and to stabilize the output to desired DC voltage.The above can be tried in practical to obtain DC voltage. The primary components needed are :
1.Tranformer ( Step-Down) 220V / 12V 1 Amp ( to design a 12 watt DC power supply).
2. IN4007 Diode 1 Amp ( Higher the output power required , higher would be the ampere rating of the diode).
3.Filter Capacitor - Polarized( Based on output wattage,you may select the amount of voltage the capacitor can be).
Optional Components : LM 2904 / 7812 to have pure 12 volts supply , 7805 to have pure 5 volts power supply.
Also , the transformer rating , diode rating , capacitor ratings must match with the output power ie , you cannot use a small 1 amp transformer with 1/4 watt diode to run a DC motor or light a series of bulbs that consume more than 1/4 wattage of DC power.
In order to have a high power output , you may either use 3/5/10 amps transformer , 10 amps diode to have a high DC power output.
Modern phone adapters ( 50 watt charger , 100 watt charger ) use different technique to obtain DC power. Instead of using transformer to reduce (Step-down) the AC supply from 220 to 12 Volts) they use diode ( 5 amps / 10 amps ) to directly convert 220 V AC to 220 V DC supply . Then using opto isolators and opto couplers and a inductive transformer circuit , they convert the AC supply to 5 volts , 10 amps DC supply . This technique is only used to charge and no motor or heavy loads can be powered using this circuit.These types of circuits are generally used in laptop chargers , display adapters and other computer parts.
The another method is using power electronics , using thyristors one can convert the AC to DC just by switching the thyristors at desired angle. These are used in rail engines and other high powered drives that are essentially used to convert high power AC to high power DC supply.These are generally preferred upon all as they are the most-efficient conversion circuits.
There is also an another method (which is considered a lossy method).This method is least considered as it has the lowest efficiency in conversion.This method is where a AC motor’s rotor is coupled with a gear system ( similar to bike’s gear system where-in as we increase the gear , the output rotor’s speed is increased ). This output ( mechanical ) ie the rotor from the gear mechanism is then connected to a DC motor. Now when AC motor starts to run , the rotor in turn provides mechanical output which is fed as input to a DC motor . Now the DC motor acts as a generator ( as all DC motors acts as generator when a mechanical input is fed to its rotor ) . Now the DC motor generates desired DC power. The varying DC voltage can be then altered using the gear mechanism ( lowest gear produces low DC voltage , highest gear produces high DC voltage
So , there are these many ways in conversion of AC power to DC power . These are purely used only based on load and how much power and dynamic currents the load requires . Ex : Starting a DC motor generally consumes high starting current.Thus opting for power electronics would be a better solution in order to avoid circuit over-heat and reduced efficiency.