Emergency stand by supply controller for ultra-fast changeover - takes derivatives of primary supply signal and reference signal and continuously compares to give changeover in less than 200 microseconds

Solid state switches exchange an electric load from the normal electric supply (51) to an emergency standby supply (52) providing high speed changeover by generating a derivative of the primary supply signal. A derivative of the reference signal is also produced, and the signals are continuously compared to provide changeover in less than 200 microseconds if the primary signal falls below the reference. Interface circuits (1,3) isolate the supplies from the changeover control circuit. The primary supply (s1) interface (11) supplies a circuit producing a reference signal (sdt). The interface also supplies a second circuit (6) which gives a derivative signal (sdv) from the primary supply signal. These two signals are compared (8). The selection of the logic signal (17,18) to determine which solid state switch is closed onto the load is determined by a logic circuit (16) in response to input signals (15,42, 21,27). DANS LE PROCEDE ON GENERE UN SIGNAL DERIVE REEL SDV QUI EST LA DERIVEE REELLE DU SIGNAL REEL S1 GENERE PAR LA PREMIERE SOURCE NORMALE S1; ON GENERE OU UTILISE UN SIGNAL DERIVE DE REFERENCE SDT; ON COMPARE LE SIGNAL DERIVE REEL ET LE SIGNAL DERIVE DE REFERENCE; SI L'ECART ENTRE LES DEUX SIGNAUX DEPASSE UNE LIMITE FIXEE, ON COMMANDE LA COMMUTATION DE LA CHARGE DE LA PREMIERE SOURCE ELECTRIQUE SUR LA SECONDE SOURCE ELECTRIQUE.