| 摘要 |
PURPOSE:To prevent a feed resistance from increasing even if a supplying current is decreased by changing a current supplying resistance magnification factor for an area where the supplying current is large and the area where it is small. CONSTITUTION:First and second feed circuits 1, 2 regulate the bias point of a transistor, and when the supplying current iL is large, the first supplying circuit 1 operates, and when the supplying current iL is small, the second supplying circuit 2 operates. Because the current supplying resistance magnification factor N2 of the second feed circuit 2, which operates at the time of the small supplying current iL, is set smaller than the current supplying resistance magnification factor N1 of the first supplying circuit 1, the current supplying resistance can be suppressed to be small even when iL is small. In addition, when an operation shifts from the first supplying circuit 1 to the second supplying circuit 2, a constant current circuit 2a is always allowed to operate. Thus, the parallel operation of the currrnt supplying circuits 1, 2 can be avoided.
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