Input circuit includes a constant current circuit

摘要

In aspects of the invention, a zap circuit and a decoder for decoding the output of the zap circuit turn ON only one analog switch in a selector. The selector delivers an electric potential at a node of a dividing resistor selected by the zap circuit. The output of the selector is delivered to the non-inverting input of an operational amplifier, and the output of the operational amplifier is delivered to the gate terminal of a MOSFET. The operational amplifier controls the gate of the MOSFET so that the potential at a current detecting resistor equals the output of the selector. As a result, a current proportional to the input voltage flows through the MOSFET. Because the current through a dividing resistor is also proportional to the input voltage, the total current is eventually proportional to the input voltage.

主权项

1. An input circuit comprising:
an input voltage detecting circuit that is connected to an input terminal, detects and input voltage, and delivers a detected voltage; and a constant current circuit that is connected to the input terminal and generates electric current flow corresponding to the detected voltage, wherein the generated electric current flow is proportional to the input voltage over a predetermined temperature range, wherein the input voltage detecting circuit is a dividing resistor, and wherein the constant current circuit comprises:
a MOSFET,a current detecting resistor connected between a source of the MOSFET and a base potential,an operational amplifier, a non-inverting input terminal of the operational amplifier being connected to a divided output of the dividing resistor, an inverting input terminal of the operational amplifier being connected to a source of the MOSFET, and an output terminal of the operational amplifier being connected to a gate of the MOSFET; and a drain of the MOSFET is connected to the input terminal.