Experiment 8 - Heat Generation of the Voltage Regulator II

You can influence the power dissipation through a smart choice of the input voltage. This is due to the fact that the power dissipation is proportional to the difference of the input and output voltage.

Replace the load resistor R1 with 100 Ω, 5 Watt...

Input voltage U_in = 9 V

Circuit diagram heat generation voltage regulator 7805.

Circuit heat generation voltage regulator 7805. (Enlarge)

The power dissipation P_D amounts to...

P_D = (U_in - U_out) × I_out

     = (9 V - 5 V) × 0.05A = 0.20 Watt.

Neither load resistor nor voltage regulator heat up.

Input voltage U_in = 18 V

Circuit diagram heat generation voltage regulator 7805.

Circuit heat generation voltage regulator 7805. (Enlarge)

now the power dissipation P_D amounts to...

P_D = (U_in - U_out) × I_out

     = (18 V - 5 V) × 0.05A = 0.65 Watt.

The voltage regulator heats up, the load resistor remains unchanged.

So if your voltage regulator gets too hot, you should try to lower the input voltage!

However, you cannot lower the input voltage arbitrarily...