Means for increasing the reliability of electronic circuits incorporating zener diodes

Claim 1

In an electrical network situated in a location difficult of ready access and normally dependent for its proper functioning on the voltage-regulating properties of a Zener diode which is subject to malfunction thereby exposing other components of the network to damage by virtue of unregulated potential excursions, the improvement which comprises: apparatus for increasing the operating life expectancy of said network, said apparatus including: a plurality of Zener diodes arranged in at least two parallel paths both of which interconnect the potential points across which voltage regulation is desired, each of said paths containing at least two Zener diodes arranged in cascade, all of said diodes having essentially equal voltage drops thereacross, whereby the plurality of diodes in each path provide effective redundancy against a malfunction of any one diode in a shorted mode, and whereby the plurality of parallel paths provide effective redundancy against a malfunction of any diode in an open circuited mode, the number of diodes in each of said parallel paths being selected so that the overall voltage variation in each path occasioned by failure in a shorted mode of any one diode in that particular path does not exceed an amount which can be tolerated by other components of said network without damage thereto and does not exceed an amount which would result from the failure in a shorted mode of any other diode in that path.