Power supply circuit and luminaire

A luminaire comprising:

• a lighting load;
• and
• a power supply circuit configured to supply electric power to the lighting load,
• the power supply circuit including:
• a bridge circuit including at least one switching element and configured to convert a direct-current voltage into an alternating-current voltage according to ON and OFF of the switching element;
• a transformer including a primary winding wire connected to the bridge circuit and a secondary winding wire magnetically coupled to the primary winding wire;
• and
• a rectifying and smoothing circuit configured to convert the alternating-current voltage output from the secondary winding wire into a direct-current output voltage and supply the direct-current output voltage to the lighting load, wherein
• when a number of turns of the primary winding wire is represented as N1, a number of turns of the secondary winding wire is represented as N2, a voltage value of the direct-current voltage supplied to the bridge circuit is represented as VDC, and a lower limit value of the output voltage is represented as Vmin, a turn ratio of the primary winding wire and the secondary winding wire is about N1:N2=(VDC/2):Vmin.