Patent ID: 7199647

Claim:
A constant current circuit in which a bias voltage of a field effect transistor is set, the bias voltage enabling a constant drain current to be supplied to a load connected to a drain of the field effect transistor irrespective of fluctuations in a drain-source voltage, comprising: a bias circuit which sets, as the bias voltage, a gate-source voltage corresponding to an intersecting point between an ID-VGS characteristic curve at arbitrary first temperature and an ID-VGS characteristic curve at arbitrary second temperature which is different from the first temperature in the ID-VGS characteristic of the drain current to a gate-source voltage of the field effect transistor, wherein the bias circuit is comprised of a plurality of semiconductor resistors having substantially similar temperature coefficients so as to be able to transmit heat to each other, wherein the plurality of semiconductor resistors construct a D/A converter which generates the bias voltage, wherein the bias voltage is set on the basis of a voltage supplied from a band gap constant voltage source.