Can I use 2 LM317 cascaded?
You can chain regulators as you suggest BUT the lower voltages will incur large inefficiencies &amp; also large power dissipation in the regulators.
Efficiency can be improved with switching regulators.
This (10 year old!) SE answer of mine to &quot;My linear voltage regulator is overheating very fast&quot; should be useful.
Linear regulator dissipation can be greatly reduced at lower voltages by using a series input resistor sized to provide adequate voltage at max current.
eg providing the 5V regulator with a resistor feed from 27V, if you assume a headroom of say 3V is needed and the regulator takes 1.25v for itself then
R = Vdrop / Imax
= (27 - 3 - 1.25 - 5)/Imax
~= 17V/Imax.
eg for say 0.5A max at 5V R = 17/0.5 &lt;= 34 Ohm.
Resistor power dissipation will be Imax^2 x R or in this case 8.W watts.
A 10 Watt resistor would be very marginally suitable and a 20 W one advisable.
Use of air cooled resistors allows use without heatsinks.
Use of series resistors also allows substantial reduction of regulator heatsinks.