Electronics > Projects, Designs, and Technical Stuff
Capacitive dropper power factor correction
OM222O:
Hello
I have seen the classic capacitive dropper, followed by a bridge rectifier used in a ton of consumer electronics (such as led lights that use mains).
They also have a TERRIBLE power factor, best ones are in the order of 10%! I was wondering if there is a way to fix that issue with an inductor somehow (the logic being that capacitors are used to correct power factor of inductive loads, so doing the reverse should be possible). I'm not sure if it affects the performance of the circuit or even if it's possible (the capacitive dropper works by creating a phase shift, correcting that probably makes the dropper useless?) I'm not really sure but if anyone knows the answer, please answer down below. Thanks.
jbb:
Well, the thing with a capacitive dropper is that they are normally used for low power applications. That means that the total VArs developed by the capacitor aren’t very high.
Also, many loads are inductive (eg non electronic motors), so having some capacitive VArs about is not a bad thing.
In principle, you could calculate the VArs generated by the capacitor during operation, and then fit an inductor between line and neutral which consumes approx that number of VArs. But you would need quite a large inductor.
Siwastaja:
The idea for such a circuit is the ultimately low cost; the inductor to store the required energy at line frequency would be too large for such small benefit.
If high power factor is any kind of priority, using a proper switch-mode active PFC quickly becomes more affordable. This is an already solved problem, with highly integrated cheap and small ICs available.
Zero999:
The inductor would need to be as large as a small transformer, so why just use a transformer based power supply?
OM222O:
Well what if the mains is rectified first (no smoothing caps), then dropped and smoothed? I'm assuming that would help with the value of the inductor? The problem with switching supplies is that they also require beefy inductors and capacitors, now add in the cost of all the ICs and protection features and I'm not sure it will be more affordable than and simple inductor to correct the power factor?
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