bforu_gs:
My transformer is 1 A, 12 volts.By 3/4/5 I mean 3 or 4 or 5 amp circuit which i can replace in my existing power supply circuit.
Thanks for clearing that up. So we have a transformer rated for 12 W on the secondary side, which in turn limits the total power available to 12 W. So theoretically we could get a maximum of 2.4 A at 5 VDC and that's assuming no power is lost during the conversion from 12 VDC to 5 VDC. In reality you could expect efficiency to be above 85%, even a bit over 90%, but not 100%.
You need to get more power from the electrical mains, at least double (24 W total). Your situtation will determine what's most practical but the basic options are; put more than one of the same type of transformer in parallel with the transformer presently in use, replace the current transformer with one that can output more current (while the main criterion is the power on the secondary side, you probably don't want to increase the voltage level), or getting a pre-made AC to DC power supply (and in this case you might as well get one in the 40 to 60 Watt range). Once you figure out which option works best for you, then you determine the method to step-down the voltage while ensuring enough current.