Patent ID: 7084638

Claim:
An electronic monitoring circuit for monitoring one of at least two series-connected capacitor units in an intermediate circuit in order to detect short-circuiting of said one of said capacitor units, said monitoring circuit ( 16 ) comprising: means for deriving a reference voltage ( 14 ) from an intermediate-circuit voltage (L(+).L(−)) applied across said at least two series-connected capacitor units ( 1 , 2 ); means for generating a control signal consisting of a voltage difference between said reference voltage ( 14 ) and a junction voltage at a junction ( 13 ) between two of said capacitor units ( 1 , 2 ); and means for generating an error signal when said control signal falls below or exceeds an activation threshold voltage thus indicating that said one of said capacitor units ( 1 . 2 ) has been short-circuited; wherein said means for generating said error signal when said voltage difference falls below or exceeds said activation threshold voltage comprises a zener diode ( 15 ) and said activation threshold voltage corresponds to a breakdown voltage of said zener diode.