MONITOR CIRCUIT USED FOR LAMP CIRCUIT MONITOR, ETC

摘要

PURPOSE: To monitor a light circuit properly at all times by producing an alarm signal when a voltage across the terminals of a sensing resistance series- connected to a load such as an external light of an automobile is lowered to below a specified value and when it is raised to above a specified value larger than that specified value. CONSTITUTION: A sensing resistance 16 for producing a small potential across both terminals when a power is supplied is installed between two external lights 10 and a control switch 12 of an automobile, and connection points of each resistance 16 to the lights 10 and the connection points of each resistance 16 to the switch 12 are connected to the terminals 14 to 16 of an integrated circuit 24. The terminals 14 to 16 are connected to the emitters of transistors 50 and 52, and produce an alarm signal when the potential is reduced to a small constant value or less. Also the terminals 15 and 16 are connected through a protective resistance 151 to the emitters of a multiple emitter transistor 150 having the same number of emitters as the light 10 so as to produce an alarm signal when a voltage across the terminals of the resistance 16 is raised to a constant value or higher which is larger than the above-mentioned small constant value.