How to save as .PNG file as default in Photoshop CS3?

by default it saves as .psd how do i change it to .png by default because its buggin to change each and every time !!

Solution 1:

The PNG format can not hold the minimum information that is contained in an image in Photoshop, even if it's a single layer RGB image. For example, the PNG format doesn't support color profiles, and an image in Photoshop always has a color profile.

So, saving as PNG is really exporting. When you load the image into Photoshop again, there is no guarantee that all settings are the same.

Solution 2:

Saving a Photoshop document as PNG is a data-loss operation. There's a specific menu to save images for the web. Good old "Save" menu is normally use for the native format.