Series feedback voltage regulator

Other Hardware General Electronics
1

Hello, below I will have a schematic of a series feedback voltage regulator.
Here is what I know about the circuit. ( If the output increases)..

If the output increases, the sampling voltage across the resistor voltage dividers increases which increases the base voltage of Q1, this causes a large collector current in Q1 and causes more current to flow through R3, which causes Q2 to conduct less, therefore, decreasing the output of the circuit and this works vice-versa if the output decreases.

Here is what I don't get, how does an increase collector current in Q1 cause Q2 to conduct less? is it because more current is flowing from the positive input through R3 and through Q1 and through the zener diode ( reverse bias) to the ground, and that cause less current to flow into Q2?
Also are both transistors biased to both be on in a steady state ( like if the output voltage or load is steady) and then compensate once changes start to happen in the circuit?
Lastly, i understand the zener diode in operating in reverse bias and acts as a reference voltage, but how does this work? Is it used as a reference voltage because it has a known zener voltage that will not change? Thanks series voltage regulator.png

series voltage regulator.png

2

Q1 and R3 form a voltage divider. If Q1 conducts more, it means the same as if Q1 was a resistor of lower value, therefore the center voltage of the divider drops, and therefore Q2 gets less base current and conducts less.

3

GalFisk:
Q1 and R3 form a voltage divider. If Q1 conducts more, it means the same as if Q1 was a resistor of lower value, therefore the center voltage of the divider drops, and therefore Q2 gets less base current and conducts less.

Perfect explanation. Thank you

4

Q1's current and R3 set the base voltage of Q2. Q2's emitter follows this voltage.

A more practical circuit (that isn't just a voltage regulator chip) is to use an opamp instead of Q1,
then you can get very good regulation due to the large amounts of feedback. The emitter follower
then acts to boost the available current well beyond what an opamp can provide - acting as
a current gain stage (current buffer).

Internally a linear regulator chip is really just an opamp, an output transistor, some current limiting and
over-temperature protection circuitry.