Patent ID: 8004284

Claim:
A leak detecting circuit comprising: a current path having one end connected to a conductor housing a device supplied with a direct-current voltage from a direct-current power source, and having another end connected to a negative electrode of said direct-current power source; said current path including a limiting resistance for limiting a current, a switch element having a first electrode, a second electrode, and a control electrode, conduction between said first electrode and said second electrode being controlled, a detecting resistance for detecting a current flowing through said current path, and a variable direct-current power source allowing a plurality of leak detecting reference voltages for detecting a leak to be selected, and having a negative electrode connected to the negative electrode of said direct-current power source; an amplifier for amplifying a voltage across said detecting resistance; and a constant-voltage circuit for making constant a potential difference between a voltage of said control electrode of said switch element and a voltage of a positive electrode of said variable direct-current power source; wherein a leak between said conductor and said direct-current power source is detected on a basis of the voltage across said detecting resistance, the voltage across said detecting resistance being amplified by said amplifier.