I need to reduce the voltage at the input of the L7812 in order to reduce the power dissipation on this component. I am using as power supply a 18Vac transformer, 8A bridge rectifier and 3x 4700uF/35V. The minimum average voltage at the output of the filter capacitor (3x 4700uF) when using the soldering station is about 20V.
I think about a resistor connected after D1 (in series with D1, on the K of D1) in order to reduce the voltage at the input of the 7812. The problem is that I cannot mount the regulators on a bigger heatsink, because I don't have any more space in the case and this is why I am asking about introducing a resistor.
I calculated that using a 33R/2W resistor should work. The average current through 7812 is about 0.12A.
I am waiting for your opinion. Thank you.