Awesome discussion guys. I have a bunch of constant current drivers that are very efficienct but have a poor power factor ~.5. I was thinking about connecting a capacitor in parallel to move the circuit closer to parity. Is that what this plug (above) does, active power factor correction?
EMI/ RFI Filters :
(...)Within switch-mode power supplies, a high dc voltage is chopped or switched at a high frequency that
can range from 50 kHz to 1 MHz.This high-speed switching process is intrinsic to switch-mode power supplies and provides its improved efficiency and reduced size when compared to linear power supplies.
However, as a side effect, this switching generates unwanted EMI. Infact, most conducted EMI within switch-mode power supplies originates from the main switching MOSFETs,transistors, and output rectifiers.
In either power supplies or electronic equipment, it is the function of the EMI filter to keep any internally generated noise contained within the device and to prevent any external ac line noise from entering the device. EMI filters usually comprise a network of passive electronic components including capacitors and inductors that form L-C circuits.
Since unwanted EMI is at much higher frequencies than normal signals, the EMI filter works by selectively
blocking or shunting unwanted higher frequencies. Basically, the inductive part of the EMI filter is designed to act
as a
low-frequency pass device for the ac line frequencies
and a
high-frequency blocking device.Other parts of the EMI filter use capacitors to
bypass or shunt unwanted
h i g h - f r e q u e n c y noise away from the sensitive circuits. The net result is that the EMI filter significantly reduces or attenuates any unwanted noise signals from entering or leaving the protected electronic device.(...)
http://us.tdk-lambda.com/ftp/other/all_about_emi_epmag.pdf
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Also ,an EMI filter serves as a " high current /surge protection "..
If a high current spike comes from the mains line towards the leds ,firstly
it will have to enter the led light fixture/circuit through the EMI filter ..
Which has a nominal operating current ...
The device's components (coils/capacitors) will fry ,almost instantly ...
Thus reducing or completely blocking ,the incomming current spike ,from rushing to led drivers
and from there to led(s)....
Passive PFC :
(...)
Passive PFC
The simplest way to control the harmonic current is to use a filter: it is possible to design a filter that passes current only at line frequency (50 or 60 Hz). This filter reduces the
harmonic current, which means that the non-linear device now looks like a
linear load. At this point the power factor can be brought to near unity, using capacitors or inductors as required. This filter requires large-value high-current inductors, however, which are bulky and expensive.
A passive PFC requires an inductor larger than the inductor in an active PFC, but costs less.
This is a simple way of correcting the nonlinearity of a load by using capacitor banks. It is not as effective as active PFC. One example of this is a
valley-fill circuit.
The Valley -fill circuit ...
(...) At start-up, the rectified line voltage is applied across C1 and C2, as they are both charged via D3 and R1, until C1 and C2 are each charged up to approximately half of the peak line voltage. When the line voltage falls into the "valley" phase, Vout begins to fall toward half of the peak line voltage. At this point, C1 and C2 begin to discharge into the load at Vout, via D1 and D2 respectively.An advantage of this design is that it is rather simple. A disadvantage is that the
ripple voltage can still be 50% of peak, and have
total harmonic distortion (THD) of 35%, which is rather high.
(...)
From what I understand the emi filter is at the AC side ..
While the PFC is on the DC side ...
Still it seems that the EMI filter does some Power Factor correction ,also ...
