(efficient) current limiting add on.

[goffery]

Dear Friends,
I purchased a simple step-up converter (2.5-5V in, %V out) with USB output socket. My intention was to use it with 3 AA batteries for portable, on-time extender or charger for smartphone. This is the simplest circuit with no protections of any kind. When I used it, hooked to my HTC, it did the job: the phone was charging. However, after several minutes the batteries, as well as the converter became VERY hot. I'd guess that the phone draws too much current, although the DCDC converter is rated to 1 A.
Now, what I would have liked to do is to add a simple, though energy efficient (if possible) current limiter. I don't know it it will be wiser to hook such a limited after the battery pack and before the converter, or after the converter, before feeding the USB. I found some interesting circuits based on L200C regulator, but I have no idea how to harness it to my needs. I thought of limiting the current to 800 or 700 mA, but I will have to tweak it for best results. Maybe better off to go simpler and add serial resistor, and loose bit energy.
I will be happy to hear your comments and suggestions, of any kind.
Best regards,
Yossi