Voltage Regulator Op Amp Circuit with Foldback current limiting

A voltage regulator circuit is analyzed in this Op Amp BJT circuit design example. This regulator is designed with operational amplifier, Zener Diode, Darlington transistor pair and a set of PNP-NPN BJT as foldback current limiter. For more Analog and OpAmp circuit examples including Analog Computers and signal conditioning please see    • Electrical Engineering, Analog, Digit...  
Note that the unregulated voltage supply at the input of this regulator is varying considerably between 14 to 20 volts. The low power 6 volt Zener diode (for example 1N5233 or MMBZ52xxBLT1G Zener Voltage Regulators) sets the reference voltage (like a bandgap) and the non-inverting op amp circuitry enforces a scaled version of the reference voltage at the output that can be adjusted by the value of the potentiometer (aka adjustable resistor). The presented voltage regulator circuit analysis shows that the regulated output voltage can be programmed between 6 to 12 volts. The minimum acceptable resistor load and the current limiting high power feedback resistor are computed as well. The Foldback current limiter functionality is explained by analyzing the roles of the set of PNP and NPN bipolar junction transistors in the current limiter feedback path that steers away op amps current when limiting output current of regulator is required. The power consumption and dissipation of the power BJT transistor in the Darlington pair is also computed.