| 摘要 |
PURPOSE:To obtain a constant current circuit possible for selecting an optional and desired temperature coefficient and less in the fluctuation of a power supply voltage by combining two circuits where the temperature coefficient of flowing current has a positive and a negative value. CONSTITUTION:The emitter area of transistors (TR) Q1, Q2 and Q3 is manufactured identically, and that of a TRQ4 is manufactured (n) times that of them. Through the constitution shown in Fig., a current I2 is given as I2=(kT/qR2)ln (n) and on the other hand, a current I3 is expressed approximately as I3 VBE/R3. Since the voltage VBE has a negative temperature coefficient, the current I3 has a negative temperature coefficient. Thus, a constant current output I0=I2+I3 is the sum of currents of the positive and negative temperature coefficients and the temperature coefficient of the current I0 is set bipolar by setting optionally the ratio of the currents I2 and I3. Then the current I2 is independently of a voltage Vcc and the current I3 is affected very slightly of the current I1 depending on the voltage Vcc, then the effect of power supply voltage fluctuation is not almost caused. |
