Dimmer apparatus

A dimmer apparatus, comprising:

• an oscillation circuit operable to change an on/off duty ratio thereof in response to one of input voltage from a rheostat light control and a variable resistor;
• a driver circuit including at least one output power transistor cyclically switched in response to an output of said oscillation circuit;
• at least one dimmer lamp being lit up by said driver circuit;
• protecting means for protecting said output power transistor when said lamp becomes short-circuited, said protecting means comprising:
• a detecting circuit for detecting short circuit current flowing through said lamp while said lamp is short-circuited, said detecting circuit including an operational amplifier responsive to a power source voltage;
• a holding circuit including a first comparator for holding said output power transistor in an off-state after a first predetermined time period in response to a detection signal of said detecting circuit;
• and
• a timer circuit including a second comparator for releasing said off-state of said output power transistor to an on-state after a second predetermined time period has passed since said output power transistor was turned off when said lamp is no longer short-circuited;
• said protecting means functioning to repeat said detecting of said short circuit current and said holding of said output power transistor in an off-state if said lamp is short circuited until said lamp is no longer short-circuited, operation of said apparatus being resumed automatically when said lamp is no longer short-circuited.