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Since LM317 is protectedagainst short-circuit, no fuse is necessary. Thanks to automaticthermal shutdown, it will turn off if heating excessively. All in all,a very powerful (and affordable!) package, indeed.
Although voltage regulator LM317 is capable of delivering up to 37V, the DC power supplyoutput circuit here is limited to 25V for the sake of safety andsimplicity. Any higher output voltage would require additionalcomponents and a larger heat sink.
Make sure that theinput voltage is at least a couple of Volts higher than the desiredoutput. It's OK to use a trim-pot if you're building a fixed-voltagesupply.
Problems:
Follow all the safety precautions when working with mains voltage. Insulate all connections on the transformer.