1. A constant-voltage circuit comprising: a first constant-current source circuit having a first temperature coefficient; a second constant-current source circuit parallel to said first constant current source and having a second temperature coefficient wherein said second constant-current source comprises: a transistor; a first resistor element connected between the base and emitter of said transistor; and a second resistor element connected in series to the collector of said transistor; and a current conversion element which can convert the sum of the current from said first constant-current source circuit and said second constant current source circuit into a voltage.