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Use a transformer to step down the 220V mains. Rectify it to DC with a bridge rectifier or full-wave rectifier. Filter the output with a large bulk capacitor and use a 7818 to keep the output regulated. You can also use an LM317. Make sure the regulator is mounted on a large enough heatsink. This method using a linear regulator is simple but inefficient. If you need an efficient approach, use a switching regulator.
Now in all the supplies you will find, it's likely that none is 18V / 1A. You might find some
spitting 18V, some other 1A capable, but both conditions reduce the probability of finding
the right one. So you may need to calculate it yourself.
1. Buy a transformer. For 18V output, you need at least 18 / root(2), let's say 13V after the
diodes, so if you add the diodes' 0.7V, you need 14.4V. Buy a 15V , 20VA transformer and
you will be safe.
2. Buy a diode bridge and a capacitor. For the diode bridge, chose one that rates more than
1A. Say 2A will be a good choice. As for the capacitor, you will have to choose it so that
it does not discharge lower than, say, 18.5V.
At the peak, you will have 15 * root(2) = 21V.
And when you discharge these 21V at 1A, it should not become lower than 18.5V after 10 ms.
3. Add a regulator (for example a 7818). And 2 other caps.
You're done.
Byt the easiest way is probably to buy a 18V adaptor, you can have a switched one for about
10 Euros and which is better smaller, more efficient, etc than anything you will do by yourself.
thanks friend what is the best method switching or regulated?
i hope to drive 2 stepper motors by using this
doraemon can you please send a circuit diagram of your circuit
In terms of efficiency, heat, etc. switching is better. But for simple and cheap, linear is better. Don't confuse "linear" with "regulated", as switching regulator also provides regulated output. Switching regulators and linear regulators just regulate the output with different methods.
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