Could somebody please help me understand this circuit?

[Joshbessant2]

Could someone please explain to me what this circuit is used for? I believe it is a full wave bridge rectifier but I'm unsure as to what the zener diode is used for in this arrangement?

Thanks in advance

 

[DPG]

It's a very basic regulated power supply. Full wave bridge rectifier, as you said, to rectify the incoming AC to DC. A capacitor to smooth the output of the rectifier. Then a zener diodes to regulate the output voltage.

 

[Joshbessant2]

It's a very basic regulated power supply. Full wave bridge rectifier, as you said, to rectify the incoming AC to DC. A capacitor to smooth the output of the rectifier. Then a zener diodes to regulate the output voltage.

Thank you very much!

 

[Simon47]

The magic words to search for are "shunt regulator".
The 100R resistor controls the current available. Any current not taken by the load will pass through the zener diode - Iz+Il is roughly constant. For a fixed AC voltage, the power dissipated will remain more or less constant - some in the resistor, the rest in either the load or the zener. One of the simplest, and least efficient, voltage regulators.

 

[Lucien Nunes]

For which reason it's no longer generally used, and only normally for very low power. It was more common in the days of fully analogue electronics, and before simple, low-cost monolithic regulators and SMPSUs with inherently regulated output were the norm.

 

[Simon47]

One reason I can think of that you may still find it in niche applications - stability and noise. While most stuff is switch mode these days, that brings with it a lot of noise. Analogue series regulators, whether built with discretes or by use of a monolithic chip, typically have some stability limits - though in practice I think they are generally hard to breach with the ones I've used.
So if you have a low power, efficiency isn't an issue, and want low noise, this may still be the best option.