On the problem of LED lamp replacing incandescent lamp

The output of 50W transformer is AC rectified and filtered,12 *1.4-1.4 =15.4v, which must be stabilized.

3W can be used, 5W 78 12 needs heat dissipation, and the power of the transformer is insufficient, so a larger transformer needs to be replaced (because the power factor is too low). I have done 3W, and the transformer 50W is very hot.