Protection circuit protecting against voltage irregularities

Protection circuits ( 1 ) to be located between power supplies ( 2 ) and further circuitries ( 20,30 ) for protecting further circuitries ( 20,30 ) against voltage irregularities and comprising main transistors ( 7 ) coupled to switching circuits ( 10 ) for rendering main transistors ( 7 ) operative/non-operative can be made more allround by providing them with comparators ( 11 ) for controlling gate voltages of main transistors ( 7 ) via switches ( 12,13 ) to get protection against small negative voltage pulses and voltage fluctuations. Said switches ( 12,13 ) comprise two switches ( 12,13 ) for interrupting a reference voltage generated by a reference voltage source and for supplying a nearby ground voltage to said gate. A diode ( 14 ) between switch ( 13 ) and gate allows negative voltages at said gate for simplifying the introduction of further stages. Thick oxide transistors ( 15 ) protect further circuitries ( 20,30 ) and main transistors ( 7 ) against large negative voltage pulses. Capacitors ( 16 ) and resistors ( 17 ) coupled parallelly to thick oxide transistors ( 15 ) protect against large negative voltage pulses and reverse polarity. Serial transistors ( 21 ) are coupled anti-serially to main transistors ( 7 ) to get protection against large positive voltage pulses.