Voltage regulator - unexpected voltage drop, is this normal?
The voltage drop in this regulator circuit from 12V to 4.5V is 7.5 Volts.
For a linear power supply, the power dissipation is \$V_{drop}*I\$.
At 0.2A this will cause the regulator to dissipate 1.5 Watts.
With 50 C/W to ambient this means an 75 degree increase in temperature.

If you did not use a proper heatsink, you're most likely running into the thermal overload protection.