You can export .psb images to .png format directly in Adobe Photoshop, which essentially covers psb to png conversion. However, by doing this you will lose any layer and other special data used by Photoshop and get a simple bitmap image.
This works only for smaller files; users will have trouble with exporting large .psd files to standard images, because of Photoshop's limit of 30k pixels. Unfortunately, we do not know about any other program that can convert psb to png or about any online psb to png converter.
Updated: April 6, 2017