Constant current bias generating circuit


PURPOSE: To avoid the effect of the variation of the power supply voltage by constituting a constant current bias generating circuit with four transistors and two resistances and to secure the specific conditions for the relation between the emitter areas of said transistors. CONSTITUTION: A constant current bias generating circuit consists of transistors (TR) Q 1 ∼Q 4 and resistances R 1 and R 2 . The TRs Q 1 ∼Q 4 have the same emitter area and the TRQ 4 has its emitter area which is (n) times as much as those of other TRQs. It is decided that the current value of the R 1 and TRs Q 1 and Q 2 is equal to I 1 and the current value of TRs Q 3 and Q 4 and the R 2 is equal to I 0 respectively as long as the current amplification factor of each TR is satisfactorily large. The relation shown by an equation I is obtained since the saturated current value is proportional to the emitter area, where (k), T and (q) show the Boltzmann constant, absolute temperature and electronic charge respectively. In the equation I the output current I 0 has no relation with the output current I 1 . Therefore it is possible to obtain a stable constant output current I 0 regardless of the power supply voltage and the resistance R 1 . COPYRIGHT: (C)1985,JPO&Japio




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