The ?Basic Linear Shunt Regulator is similar to the basic linear regulator ?with a few differences. The main difference is that the Linear regulator ?uses a series pass transistor for a cont

The  Basic Linear Shunt Regulator is similar to the basic linear regulator  with a few differences. The main difference is that the Linear regulator  uses a series pass transistor for a control component, while the Basic  Linear Shunt Regulator uses a transistor in a parallel with the load for  its control component. There are 4 main parts to this type of regulator  which are; a reference voltage, error detection, a control element (the  shunt), and a sample circuit. 

R1 is placed in series with the load, and works like a series  regulator but instead regulates by regulating the current passing  through the control element (Q1). When the value of the output goes to  decrement due to the change in input voltages or load current made from  the variation in the load resistance it can be observed from resistors  R3 and R4. The resultant voltage decreases the op-amp output to decrease  its collector current value while the collector voltage rises. This  allows for the variation in voltage to be overcome and keep the value of  the output steady and constant. 

H. (2021, January 30). Introduction to Linear Shunt Regulators – The Engineering Knowledge. The Engineering Knowledge. https://www.theengineeringknowledge.com/introduction-to-linear-shunt-regulators/