It is a Vo control circuit by passing part of the load current (output current) through the control component connected in parallel with the load. This type of regulator is usually used for variable loads, if the load is light it means it requires a small current so that the load voltage (Vo) tends to increase and if the load is heavy it means the opposite.
Regulator Concept
In parallel voltage regulator, some of the current from the input voltage (Vi) is also passed to the control element (Ish) sampled and given to the load (IL) if there is a change in load (IL up/down) then the output voltage also tends to change, this change is felt by the sampling circuit and will then provide a feedback signal. To the comparator based on the feedback signal and reflection voltage will provide a feedback signal to the controller so that it can flow the Ish current according to needs, thus providing a stabilizing effect on the Vo voltage.
Basic Regulator
Transistor Q1 functions as a control element that passes some of the load current to stabilize Vo. The reference voltage is obtained from V2, if RL drops then the VbE voltage drops, so that the transistor conducts less, therefore I (+) also drops and the load current increases, thus the transistor tries to increase the output voltage (so that it becomes stable).
Vo = Vz + VbE
To get better stabilization, an Op-Amp IC can be added, then the load changes will be felt by the sampling circuit in the form of a voltage divider R1 and R2, then this feedback signal is compared with the reference voltage by the Op-Amp to then be used as a control signal for transistor Q1. The magnitude of the output voltage can be calculated.
Vo = { I+ (R1/R2) } (Vz)
Power Supply Regulator Case Study, Scheme 1
Op-Amp and Zener Diode as Stabilizer
DTMF Switching Multiplexer
| | C1 | C2 | C3 |
|----|----|----|----|
| R1 | 1 | 2 | 3 |
| R2 | 4 | 5 | 66 |
| R3 | 7 | 8 | 9 |
| R4 | * | 0 | # |