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Just came here from the LED flickering video, and considering it's 1AM in the states, this is gonna be my bedtime reading for tonight :)

I can't add these annotations links until the video is finished processing. And if the video goes live while I'm asleep, well, it can take some time to add them. And yes, sometimes I just plain forget too.

I love your idea of bedtime reading Dave!

Speaking of bedtime reading. I've watched one or more of your videos before bed most days for the past few months.

You are my bed time reading! Thx!

Great video, I kinda miss the older videos you made (the reason I started watching), the ones with the mini white board and easy to understand explanations. I respect your knowledge of the subject.Anyone can open something up and wave a camera around inside, but yourself (and Mike's elec) add that extra level of understanding. It might just be me but the later videos are somewhat dumb down a little? I guess it attracts a wider audience? but it's slippery path to smashing up tv's to get views! ;)

I thought I might be a little bit nerdy but this night time topic puts you way above me :D

i would love if you could somehow plot the input volt and amp curves on a device with a poor power factor. (seeing that sag) and perhaps multi channel to see the difference the chip actually made, side by side.. or do a video on different methods of active PFC, how they work, etc.

The on time remains constant. The reason they use a bridge rectifier followed by a boost PFC converter is to allow PFC. It would be too much trouble and bulk going with a transformer, not to mention you lose PFC capability. With power factor correction, you're able to draw the minimum line current for the maximum output power. There are standards like the EN 61000-3-2 that dictate the maximum current harmonic content you can produce and without PFC, you wouldn't be able to meet this requirement

Motorola is a multi-department corporation. Each department takes a different sector of manufacturing. Motorola spun off two companies from their semi-conductor branch, one being ON Semiconductor, and the other being Freescale. The reason for spinning off these other companies can vary, but it usually ends up being cheaper for them.

I think you did right to separate this part from the other video. Whoever searches for PFC will find it (like me) and get a huge chunk of pointers on how to design their own DC PSU circuits. As an electrician in an industrial company in Germany I know how dirty a power grid can get if machine suppliers are not careful, waveform wise that is. The choice of the type of VFD can make a huge difference in that regard.

Thank you so much for this interesting video

Dave, good overview mate.

I worked for KW Controls which had UPS system from .5 kva to 1000kva They had TUPPS system transistor uninarutable power system . I was trained to work on all the systm including QA testing which includes power factors on all the systems . This was the late 80s I worked there for 6 years . They also had Piller systems

Relatively stressful, yes, but you'd just spec suitable components to handle it of course. RU-vid doesn't allow links in comments, it has to be obfuscated.

I was wondering what will happen if we replace the AC input with DC one , for e.g instead of 240v AC we supply 345v DC , how would this circuit will response ?

Great vid as always! 5:48 -> In the notes it says to let n = 0.92 for low line operation. What is low line operation? Trying to grasp but AC fluctuates so confused to what low line, or high line would be? Where are they deriving n from? Is n the efficiency of the chip, or the entire pfc stage?

Because APFC circuit is designed to work with rectified sinusoidal voltage.

Hah, after watching the last video I went straight for the MC34262 data sheet to figure out how the PFC scheme works. Nice choice of topics ;).

This is the *real* eevblog stuff I come for. :)

Just discovered this. I’ve also read some abstracts on using synchronous rectification and using that to control pf too in a more simplified design. Have you done a video on that? Couldn’t find anything.

What happen to spinning power meter if the load are just half wave rectifier with capacitor power supply. Will the disc still spinning since the current form is just on one side or DC.

bridge rectifier into caps is nice and efficient, but not for the power company, and maybe also for their consumption metering / billing systems... I'll stick with the old ways unless theres a real need for anything else that improves the equipment in use.

I think a video on why we need power factor correction would have been good to have before this one.

Love your videos!

If you listen carefully, most professional announcers have a big bass component and a matching treble component. The two sound great together, but if you put it through a lo-fi path (POTS line), these roll off at both ends and you can barely recognize the speaker. Dave's probably has a big mid-to-high-freq peak, so he's tailored for those 99-cent earbuds. Just the thing for iPod listeners and utilitarian comm channels. :-)

Hi Dave I sometimes notice power factor is low at low power consumption, why this happens?

Dave, you sometimes add these "click here" texts in the video, but you always seem to forget to add a clickable annotation over the text.

Why do they rectify first, then use a DC to DC converter? To me it would be easier to use an transformer to bring the voltage down, then rectify. I am sure there is a reason why it is done the way it is but I was wondering why.

Sir can I get the MATLAB simulation of this pfc...

OK thanks.

I love his voice :D

Money is the reason. With a big transformer, you need uh, a big transformer. That's lots of iron and copper. The DC-DC starts by generating AC at 100KHz or whatever, which allows little transformers to be used. It's also smaller and lighter, allowing more product to be jammed into a container, which is important because it all comes from China. If you are going to have regulation ckts anyway, might as well have them doing the DC-DC thing at the same time.

Yet another video that fails to reveal the magic smoke. Problem statement: A simple rectifier into capacitor power supply draws current only when the incoming sine wave happens to have a higher voltage (plus 2 diode drops) than the capacitor. At that moment, the capacitor starts charging and its effective resistance nearly zero thus current demand is very high, but only for a few milliseconds. Solution statement: Find a way to spread out that spike that happens 120 times per second; find some way to extract energy from the entire sine wave not just the peaks. Complicating factor: The filter (bulk) capacitor already has 300 volts on it. At the moment the incoming sine wave is 20 volts. How are you going to step up that 20 volts to 300 so it will impart some energy to the capacitor? You cannot just use a 15 to 1 step up transformer; if you do that, watch the smoke happen at the peak of incoming voltage! The magic is a FLYBACK regulator; known here as a boost regulator but it depends on the flyback effect of the inductor. This is the same phenomenon that generates the spark in your gasoline powered internal combustion engine. Inductor charging half-cycle: For a few microseconds, the inductor is *shorted to ground* which seems like a bad thing but while shorted to ground it is building a magnetic field. Then you suddenly open that path to ground. Capacitor charging half cycle: The magnetic field starts to collapse. It wants to push electric current in the same direction that it has been flowing. What is special is that it does not care about voltage; it will push X number of electrons up a very steep hill if necessary. So, even though the capacitor already has 300 volts on it, and you charged the inductor at a moment where the incoming sine wave had only 20 volts, when you interrupt the ground path, the inductor will push 20 volts no matter what; making a spark if it needs to. It pushes that 20 volts right onto the 300 volts already on the capacitor and THAT is how you glean energy from the 20 volt (or any volt) portion of the incoming sine wave and scoop it up on top of your storage capacitor. Detailed nuance: We don't actually fully charge the inductor, that would be bad, and we don't completely dump the charge either. So we "top off" the capacitor with these little impulses and in that manner spread out the consumption of CURRENT from the source so that the current approximately follows in shape and phase with the source voltage. It is by its very nature current limited since the thing that charges the main storage capacitor is the FLYBACK impulses from the inductor. You doubtless notice an interesting phenomenon; at the source peak voltage, the duty cycle on the inductor pulse width modulation is LEAST. That's because it only takes a few microseconds of high voltage to "charge" the inductor; but as the voltage goes down following the sine wave, the pulse width will expand in order to maintain the magnetic field charge on the inductor. It will expand across all cycles as the load increases.

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