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The figure illustrates a DC current regulator circuit which is specially useful in an automatic DC line current regulator for telephone line couplers.
English (United States)
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Automatic DC Current Regulator Circuit
The figure illustrates a DC current regulator circuit which is specially useful in
an automatic DC line current regulator for telephone line couplers.
The input current Iin to be regulated is mainly divided into currents I1 and I2
which enter two parallel paths and regulate each other.
A variation delta 11 of current I1 causes current I2 to vary by
an amount, delta 12, whose value is given by
delta I2 = r/R6 delta I1
where r is the dynamic resistance of a diode.
As resistance r is much smaller than R6, current I2 can be considered to
have a constant value. Transistor T4 works with a constant load and its base-
emitter voltage, Vbe, is maintained at a constant value which maintains a
constant voltage across resistor R5, thereby maintaining current I1 at a constant
Current I1 is selected to be much greater than current I2. Resistor R5, which
is a low value resistance, defines the value of current I1. Transistor T1 and
resistor R6 define current I2 value. To dissipate the power lost in the regulator,
current I1 is divided into two equal currents by means of identical transistors
T2,T3 and resistors R1,R2,R7,R8. Resistors R3 and R4, high value resistances,
are start-up resistors. Diode D3 protects transistor T4 against lightning surge
effects. Zener diode DZ1 protects the regulator circuit against those effects and
shunts any overcurrent caused by an overvoltage.
The regulation coefficient depends on the R3 and R4 resisto...