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Series regulators vs shunt regulators..

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randolfo

New Member
I am bit confused on the following choices, which one statement about series regulators is correct ?

1) Series regulators are inherently less efficient than shunt regulators because the current through the shunt regulator flows through the load.
2) Series regulators are inherently more efficient than shunt regulators because the current through the shunt regulator flows through the load.
3) Series regulators are inherently less efficient than shunt regulators because the current through the shunt regulator does not flow through the load.
4) Series regulators are inherently more efficient than shunt regulators because the current through the shunt regulator does not flow through the load.

I am inclined to choose no. 2, I don't know I am confused between no. 2 and no. 4 , do you have any idea or comments about series regulators vs shunt regulator ? Am I getting it right ? Please help . :)
 

crutschow

Well-Known Member
Most Helpful Member
Have you looked at a schematic for a shunt regulator? You would then know where the current flows and could answer the question.
 

MrAl

Well-Known Member
Most Helpful Member
Hi there,


I hope you do take the time to look at the circuits for both series and shunt, but
i also hope that the following doesnt confuse you even more...

"Efficiency" is not the only issue concerning series and shunt regulators, and
is not always the determining criterion for deciding what kind of regulator to use.
Sometimes shunt regulators end up being the better choice, and sometimes
series regulators end up being the better choice. It depends a lot on the actual
application it will be used in and not always on the efficiency. Other things like
input-output differential and nominal output load current and even total available
power often make the deciding choice.
 

bountyhunter

Well-Known Member
I am bit confused on the following choices, which one statement about series regulators is correct ?

1) Series regulators are inherently less efficient than shunt regulators because the current through the shunt regulator flows through the load.
2) Series regulators are inherently more efficient than shunt regulators because the current through the shunt regulator flows through the load.
3) Series regulators are inherently less efficient than shunt regulators because the current through the shunt regulator does not flow through the load.
4) Series regulators are inherently more efficient than shunt regulators because the current through the shunt regulator does not flow through the load.

I am inclined to choose no. 2, I don't know I am confused between no. 2 and no. 4 , do you have any idea or comments about series regulators vs shunt regulator ? Am I getting it right ? Please help . :)

I'll tell you that your assumption is not correct:

I am inclined to choose no. 2
 

RCinFLA

Well-Known Member
A shunt requlator must be designed to match the worse case load delta. Another way to say it is input supply to shunt regulator always draws same constant (maximum) current regardless of what load actually needs. Current either goes into load or dissipated in shunt regulator.

4) is best answer.
 

crutschow

Well-Known Member
Most Helpful Member
Last edited:

colin55

Well-Known Member
Answer 4 may be correct but it is a very bad question.
It is a bit like saying "woman are the best because they wear high heel shoes." - because the current through the shunt regulator does not flow through the load. It should include: it is wasted current. That's the real explanation.

The answer should be:
Series regulators are sometimes more efficient than shunt regulators.
That is ALL YOU CAN SAY.
The previous poster provided a very good, detailed description, of all the complexities of a shunt vs series regulator.
That's why questions like this are not really educating the beginner - they are confusing him.
 

MrAl

Well-Known Member
Most Helpful Member
Hi again,


I would have to agree that it's better to say 'sometimes' because that's just
about what it comes down to.
Although series regulators allow the current to flow to the load, the actual
efficiency depends on the voltage input to output differential, and with the
shunt regulator it depends a lot on the source resistance as well as
input output differential.

Maybe a better way to look at this is to say that the series regulator works
best when the efficiency is higher than that which could be attained when
using a shunt regulator, and vice versa (not a joke, but is kinda funny huh?).

If the series regulator pass element absorbs more power than a shunt regulator
shunt element(s) in the same application for the same operating conditions
and the operating conditions are stable, then the shunt regulator is a better
choice, and if not then the series regulator is.

Also, sometimes the power available is not enough to power both the load
and the series regulator, so a shunt regulator designed just right has to be
used.

All this means that there is no direct answer to the original question, and may
involve the following list of considerations:

1. Input to output differential.
2. Total power available vs total power output.

Feel free to add to the list.

In some slightly more elementary texts, the answer yes would be #4 but they
usually constrain the class of regulators and power demands and stuff like
that, where in the real world there are actually more possibilities.
The only reasoning then usually ends up being something like:
"The series regulator is more efficient than the shunt regulator because the
current flows though both the regulator AND the load, whereas the shunt
regulator shunts some of the current away from the load".
That might be considered a 'normalized' statement about the two types of
regulators, but unfortunately it's not always true as we all know.


The real tug of war between the two regulators can be summed up as
a consideration of the voltage drop of the series regulator vs the amount
of current actually shunted by the shunt regulator. Which one causes the
least power loss in the expected operating environment? That's the best one.
 
Last edited:

colin55

Well-Known Member
It also depends on the variation in LOAD. In other words, if the load varies a small amount, the shunt regulator can be more efficient, but if the load is very heavy for only 10% of the time, a series regulator may be the best solution.
It's very complex and the answer is to work out both cases and decide after a complete assessment. But to give a question like the one above is absolutely absurd and steers the beginner in the wrong direction.
 

MrAl

Well-Known Member
Most Helpful Member
Hi Colin,


Oh yes good point. It's also interesting that although the series regulator is
used most, every person reading this thread (well almost) is using a shunt
regulator even if they dont realize it if they have an ATX power supply in their
computer :)
 

Bella749

New Member
Sorry to dig up an old thread, but hoping someone could help me out. I am far from an electronics genius, but I do understand basic electrical theories and principles.

I'm looking to replace the voltage regulator on a Ducati superbike. The OEM regulator is a diode shunt type, and fail regularly. My options for replacement are MOSFET shunt or series regulator.

The charging system is 480w, 3-phase. The bike's electrical demand is typically about 75w @14v with street lighting on; maximum demand is probably about 250w for short periods if both radiator fans happen to be running.

Which regulator type would be the better choice? As I understand, the series regulator will be easier on the stator and can free up some power at the crank (albeit not much ~.5hp), due to less current draw than the MOSFET. The regulator will be operating in a hot environment, if that is a consideration.

Thanks in advance!
-Matt
 
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