bananasiong said:
but do u know that, i pick it from the bonzana's book? try to respect others.
Just because it was in a book doesn't mean it's any good!, and it's still a VERY poor circuit, and doesn't deserve any respect!.
The example I gave the link to is from a magazine robot called Cybot, it's not intended to be copied 'as is' but as an example of how an H-bridge works. I wouldn't say it's a great example, but it is considerably better than the NPN only example!.