Sub-regulators for biasing circuits

The sub-regulators for biasing circuits represent a further development of Zener-diode voltage regulators. The line resistor is substituted by a line transistor which is controlled by the current in the Zener-diode equivalent circuit. Introducing this control link one obtains a feedback circuit which preserves the current in the Zener-diode equivalent. This approach improves rejection of power supply voltage variations in the output voltage. It also reduces the output impedance of the regulator which, in turn, reduces the influence of load variations. Introducing the feedback requires attention to the circuit stability, and the proposed electronic circuit provides a simple elimination of the stability problem. The example of sub-regulator design is given, and the simulations confirm the validity of the approach.