Abstract: A circuit for protecting an electric load against reverse polarity is provided by using a MOSFET (metal oxide semiconductor field-effect transistor), wherein: the circuit is connected on the input side to a voltage supply and on the output side to the load; the source connection of the MOSFET is connected to the voltage supply; the drain connection of the MOSFET is connected to the load; the circuit has dynamic behavior similar to a diode and at the same time low power loss; the gate of the MOSFET is connected to the collector of a first bipolar transistor; the source of the MOSFET is connected to the emitter of the first bipolar transistor; the base of the first bipolar transistor is controlled by a control current; and the control current is derived from the voltage at the drain of the MOSFET.

Abstract: Power source, in particular for use in a databus in public means of transportation, wherein the power source has a first transistor (T2), and wherein in a normal operating mode of the power source the current (IA) which is conducted through the first transistor (T2) is determined by a first resistor (R3) at the emitter of the first transistor (T2), is characterized with respect to safe operation accompanied by the smallest possible space requirement and lowest possible manufacturing costs in that a temperature-dependent resistor (RV1) is thermally coupled to the first transistor (T2) and that the temperature-dependent transistor (RV1) is connected to the power source in such a way that when the temperature of the first transistor (T2) is rising the temperature-dependent resistor (RV1) influences the voltage across the first resistor (R3) and thereby brings about a reduction in the output current (IA) of the power source.

Abstract: A circuit for protecting an electric load from overvoltages has an n-channel MOSFET (metal oxide semiconductor field-effect transistor) (T1) and a means for producing a reference voltage in order to achieve the most effective overvoltage protection possible by means of the cheapest and most compact circuit possible, wherein the means for producing a reference voltage is connected to the gate of the MOSFET (T1), wherein a supply voltage is applied to the circuit on the input side and wherein the gate is supplied with a voltage greater than the supply voltage using an auxiliary voltage source in such a way that the MOSFET (T1) is turned on.

Abstract: Power source, in particular for use in a databus in public means of transportation, wherein the power source has a first transistor (T2), and wherein in a normal operating mode of the power source the current (IA) which is conducted through the first transistor (T2) is determined by a first resistor (R3) at the emitter of the first transistor (T2), is characterized with respect to safe operation accompanied by the smallest possible space requirement and lowest possible manufacturing costs in that a temperature-dependent resistor (RV1) is thermally coupled to the first transistor (T2) and that the temperature-dependent transistor (RV1) is connected to the power source in such a way that when the temperature of the first transistor (T2) is rising the temperature-dependent resistor (RV1) influences the voltage across the first resistor (R3) and thereby brings about a reduction in the output current (IA) of the power source.

Abstract: A circuit for protecting an electric load against reverse polarity is provided by using a MOSFET (metal oxide semiconductor field-effect transistor), wherein: the circuit is connected on the input side to a voltage supply and on the output side to the load; the source connection of the MOSFET is connected to the voltage supply; the drain connection of the MOSFET is connected to the load; the circuit has dynamic behavior similar to a diode and at the same time low power loss; the gate of the MOSFET is connected to the collector of a first bipolar transistor; the source of the MOSFET is connected to the emitter of the first bipolar transistor; the base of the first bipolar transistor is controlled by a control current; and the control current is derived from the voltage at the drain of the MOSFET.