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Discuss Could somebody please help me understand this circuit? in the UK Electrical Forum area at ElectriciansForums.net
![[ElectriciansForums.net] Could somebody please help me understand this circuit?](https://electricians.s3.eu-west-1.amazonaws.com/data/attachments/71/71998-a824139b8f80d3e062be8b0bec77a43b.jpg)
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.
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.
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.
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.
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.
So if you have a low power, efficiency isn't an issue, and want low noise, this may still be the best option.
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