I wan to know can i provide 5v , 1.5 amp output from transformer to atmel 328p ic of arduino uno...??
You can power the UNO with regulated 5 volts on the 5V pin, NEVER AC from a transformer without rectification and regulation.
ya currently i am using 500 ma , 12v transfoemer, then rectification circuit along with 7805 voltage regulator ,then i provided regulated output to atmel328 ic, but i want more current in output... so can use 1.5 amp output transfomer, along with rectifcation circuit, then provided output to controller?
outsider:
You can power the UNO with regulated 5 volts on the 5V pin.
Just curious if the onboard voltage regulator is happy with 5V fed into its output?
Personally I would use the Vin pin; but in that case the 5V rail is no longer 5V (more like 4V).
// Edit
The Arduino spec states that it can be powered by a 7-12 V power supply. So a 12V transformer, rectifier and 7809 (or similar) might be a better option. Do not forget to cool that 7809.
Source: https://www.arduino.cc/en/Main/ArduinoBoardUno
Operating Voltage 5V
Input Voltage (recommended) 7-12V
Input Voltage (limit) 6-20V
@sterretje
Put my ear to the board & didn't hear it crying 
.
Seriously though, I've done it more than once and never had a problem, do you think it may be harmful?
Hi,
Why do you need more output current.
If it is for external components that will be supplied directly from the supply, then that is okay.
If you are going to have more than 500mA through the Arduino UNO Board then it is not okay.
I think you need to read up on current and voltage, the power supply is regulated to 5V ALL the time as long as your load draws up to BUT NOT exceeding 500mA
Changing your supply to 5V and 1.5A, will still provide 5V ALL the time as long as your load draws up to BUT NOT exceeding 1.5A.
If you increase the capacity of the transformer you will have to increase the capacitors and fit a heat sink to the regulator.
Check the spec of the regulator to see what its maximum output current is rated at as well as your rectifier.
Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?
Tom... 
Reply 6 +:
Yes, the circuit board traces are designed for the current the onboard regulator can supply/allow, trying to push more than that through it could damage or destroy it.
outsider:
@sterretje
Seriously though, I've done it more than once and never had a problem, do you think it may be harmful?
The voltage regulator does not get power on its input so it might very well be a high-impedance output in which case there is no issue. But I'm always very reluctant to connect an output (voltage regulator) to an other output (power supply).
You can power it directly on 5v. However, you should probably not connect it to USB when it's connected that way (there's some disagreement on how critical this is - some say the fears are overblown, others say you must not ever let USB and external 5v be connected at the same time.). One common recommendation is to put 5v input in through a USB cable, instead of the 5v line, which thus physically prevents you from connecting both power sources at once.
What else are you powering with 5V? A motor? Power motors and servos separately.