Abstract: In a multiplex system for automotive vehicles, battery (+V) current is supplied to each load (70, 71) connected to a non-intelligent slave unit (20) via a power switch (TR) in the slave controlled by a capacitor (CT) which is charged or discharged in an assigned time slot by high or low voltage (A,C) applied on a low current signal line from a remote intelligent unit (10). If a load (70, 71) goes open-circuit then a voltage source (TR1, Z1) in the slave provides low current via a resistor (R2, R3) and the forward direction of a zener diode Z to charge the capacitor CT to an intermediate voltage which is detected at the remote intelligent unit (10) during an assigned load driving time slot.

Abstract: In a multiplex system for automotive vehicles, battery (+V) current is supplied to a load (70) connected to a non-intelligent slave unit (20) via a power switch (TR) in the slave controlled by a capacitor (CT) which is charged or discharged in an assigned time slot by high or low drive voltage applied on a low current signal line (42) from a remote intelligent unit (10). If the load (70) goes short-circuit then a thyristor (TH) adjacent the power switch (TR) turns on to turn off the power switch (TR) and provide a discharge path for the capacitor (CT) via the load (70), this discharged condition being detected at the remote intelligent unit during an assigned load driving time slot. Thus a dedicated extra channel (time slot) is not required at the slave unit for short-circuit testing of the load.

Abstract: A battery (+V) operable information handling and control system, for example for an automotive vehicle electrical system, has a central unit (10) and a number of remote units (20) each connected to the central unit (10) by a respective signalling link (40). The central unit (10) includes processing and control circuitry (13) and power supply circuitry (11) which are turned on to operate the processing and control circuitry (13) in an active mode of the system and are turned off in a sleep mode of the system. During the active mode the processing and control circuitry (13) applies a clock pulse voltage to a data line (41) in each signalling link (40). One of the clock pulse lines (41) is connected to power supply control circuitry (12) in the central unit (10) and to activation voltage drive circuitry (80) in the respective remote unit (20).

Abstract: A manually operable electrical toggle switch (60) is connected in a low current signalling link (40) via a non-intelligent slave unit (20) in a time slot assignment multiplex system for automotive vehicles to an intelligent master unit (10) which in response to a binary input from the switch (60) provides an output signal on such a signalling link (40) to control high current to a load (70) connected to a slave unit (20). The switch (60) has conductive plastics contacts (63) to avoid oxide corrosion problems and may be all plastics. The binary input from the switch (60) is provided by one of two resistances (R2or R3) which are distinguishable in the master unit (10) from each other and from both a short circuit and an open circuit in the signal line (42) of the link (40).

Abstract: A switching circuit has a solid state power switch (9) which is either a PNP or NPN transistor or a VMOS p- or n-channel device. Three individual sensing circuits (2, 3, 4) are set to indicate whether a predetermined operating characteristic of the switch (9) is greater or less than a given threshold value and thus to indicate if a fault is present in the switch (9) or the load (L) it supplies. Digital logic circuit means comprising three logic circuits (5, 6, 8) produce two digital signals from the output signals of the sensing circuits respectively indicating if a fault exists and if it is a serious fault or not. A circuit (7) comprising gating means disables the switch (9) in the event of a serious fault and a delay circuit (33, 34) is provided associated with the logic circuit means to prevent current surges due to short circuit faults being confused with normal operating current surges in switch on.