Power supply

A power supply, comprising:

• a step-down chopper unit which includes a choke coil and a switching element to step down a DC voltage from a DC power source by switching ON/OFF of the switching element such that a voltage required for lighting is applied to a light source;
• a dimming control unit which controls driving of the switching element based on a dimming signal, and dims the light source by alternately repeating a switching ON period during which a drive signal having a frequency higher than that of the dimming signal is supplied to the switching element and a switching OFF period during which the supply of the drive signal to the switching element is stopped;
• an inrush current prevention unit which includes a parallel circuit of a thermistor having a positive temperature coefficient and a thyristor using as a drive voltage an induced voltage of a secondary winding of the choke coil, and prevents an inrush current occurring when the DC power source is turned on;
• and
• a compensation unit which applies a drive voltage to the thyristor in the switching OFF period.