Power control circuit

A power control circuit comprising:

• a switching regulator for converting voltage of external electric power into a medium voltage, said switching regulator including a first transistor, a smoothing circuit connected to the first transistor and a first control circuit for controlling switching operation of the first transistor;
• a series regulator for converting the medium voltage to a prescribed voltage of output power to be supplied, said series regulator including a second transistor and a second control circuit for controlling conductivity of the second transistor to regulate voltage of the output power to be constant, an overvoltage detecting circuit for detecting an overvoltage of the medium voltage, and an overcurrent detecting circuit for detecting an overcurrent supplied to said series regulator;
• and
• means for operating one of said switching regulator and said series regulator under a protective condition if one of the overvoltage and overcurrent is detected,
• wherein said means turns off the first transistor if the overvoltage detecting circuit detects voltage higher than a prescribed threshold level and controls the second transistor to limit current flowing through the second transistor if the overcurrent detecting circuit detects current larger than a prescribed current level.