Electronic – Pros and cons of low-power integrated series voltage regulators vs. shunt regulators

circuit-designlinear-regulatorvoltage-regulator

TL431 (and equivalent) shunt regulators are jellybean parts nowadays and quite cheap. The same can be said of TL317 (low-power version of LM317) adjustable series regulator.

When applied to supplying power to light loads (<100mA) they are both quite effective and simple to use. Despite their different internal topology, it seems that they can be used in the same role quite interchangeably.

I was wondering what are the pros and cons of using one or the other, or, more generally, what are the pros and cons of using a low-power shunt vs. series linear regulator. What are the design decision that can make a designer choose one over the other?

I'm aware that, for example, series regulators may have considerable drop-out voltage (2.5V for TL317), something that shunt regulators don't have (but may have higher minimum bias/quiescent current, instead). But taking into account LDOs regulators, this doesn't seem to be so compelling nowadays.

In the end, are there conspicuous advantages of one topology over the other (and in which case), especially when powering low-power loads?

Note: direct comparison of the two jellybean parts I've mentioned is appreciated as well as a more general comparison between topologies. You choose. The important thing is I'd like practical considerations based on actual design experience or knowledge on reasonably current products or systems. In other words "why and when a design engineer would use one over the other".

Best Answer

To me the critical difference is how they handle loads with varying power requirements.

A shunt regulator will always take the same power from the supply, even if the current drawn by the load is reduced. In some scenarios this could be a positive feature.

A series regulator will take less power from the supply if the load current drops. In some scenarios this could be a positive feature. This also makes the series regulator more tolerant of sloppy design --- you don't have to know exactly the maximum and minimum power that might be needed by the load in order to design with the series regulator, and your design is not penalized (with extra heat generation) if you overestimate the load's current requirement.