Circuit for generating a reference voltage that varies as a function of temperature, in particular for regulating the voltage at which a battery is charged by an alternator

A regular for regulating the voltage at which a battery is charged by an alternator, comprising means for comparing a voltage output by said alternator with a reference voltage and for controlling accordingly an excitation current of said alternator, and a circuit for generating said reference voltage so that it varies with the temperature at least in a selected temperature range, wherein said circuit for generating said reference voltage comprises:

• a source of voltage that is fixed regardless of temperature;
• a pair of first and second bipolar transistors provided in an integrated circuit, the bases of which are interconnected and the number of emitters of which are different from each other so as to have different temperature behaviors of the base-emitter junctions,
• a pair of current sources for applying constant currents to said pair of bipolar transistors, respectively,
• a first resistor connected between the emitters of said pair of bipolar transistors, so that the current through said first resistor varies as a function of the temperature to which said pair of bipolar transistors are exposed,
• a second resistor connected between said source of fixed voltage and an output for said reference voltage, and through which a shifting current may flow,
• a third transistor connected between said output for said reference voltage and one terminal of said first resistor, and through which said shifting current may flow, said shifting current being equal to the current required in addition to the current supplied by one of said current sources when the current through said first resistor increases due to an increase of the temperature to which said pair of bipolar transistors are exposed above a selected critical temperature,
• whereby said reference voltage is shifted from said fixed voltage by a value equal to the voltage drop caused by said shifting current in said second resistor and varies as a function of said temperature.