The Most Important Circuit for our Electrical Future?! (PFC) EB#55

Summary

Highlights

• A perfect example using a heat gun and an LED strip highlights PFC issues. 🔍
• PFCs minimize reactive power by balancing capacitance and inductance. ⚖️
• GreatScott! shows how to build an active PFC using readily available components. 🛠️
• Emphasis on the future need for PFCs due to regulatory demands. 📜

Key Takeaways

• Power Factor Correction (PFC) helps in reducing reactive power and improving energy efficiency. 💡
• Active and passive PFCs are crucial in making our electrical appliances draw current more efficiently. 🔌
• The video demystifies PFC using simple analogies like the foam-to-drink ratio for real and apparent power. 🥤

Overview

The Most Important Circuit for our Electrical Future?! (PFC) EB#55 Transcription

• 00:00 - 00:30 This heat gun here is pure perfection while this LED strip is straight up garbage! Wait what? The reason why I am saying this, is because when looking at the current consumption of those two loads we can see a a remarkable difference. First off the heat gun, which draws current exactly in phase with our mains voltage and its shape also almost looks like it aka sinusoidal,
• 00:30 - 01:00 lovely. But next we got the terrible LED strip which draws current abruptly and only for a short amount of time near the peak of our mains voltage. OK, so what is the problem here? I mean both devices seem to work perfectly fine. Well, the problem is that the LED strip with its AC to DC power supply draws a lot of apparent power from the power grid because of the weird
• 01:00 - 01:30 current waveform; while the real power it actually requires to do its job of lighting up LEDs is rather small in comparison. That is a huge problem because nowadays we got tons of AC to DC power supplies in our homes and if they would all perform this bad then our power grid will have to face some big challenges in the future. But it doesn't have to be this way and that is why such Power Factor Correction circuits
• 01:30 - 02:00 or PFC for short do exist. And in this video I will show you what they can do, how we can make them and why they are super important for our electrical future. Let's get started This video is sponsored by Mouser Electronics who not only offer a huge selection of electronics components but also development boards. And
• 02:00 - 02:30 I am not talking about microcontroller boards or similar, even though they also have them. No, I am talking about development boards build around the newest ICs and technologies; which also includes functional PFCs that you will see later. If you are curious for more then head over to Mouser Electronics or check the link in the video description. Now let's start off with a popular analogy which is the foam to drink ratio.
• 02:30 - 03:00 You see, the liquid alone represents our real power aka the power that actually gets used to light things up, heat things up or for example charge your phones battery. But as you can see that is not all in our glass which in total represents our apparent power and that is the power your energy provider actually has to deal with in its grid so that
• 03:00 - 03:30 you can get your desired real power. No, we still got the foam which is our reactive power and truth be told completely useless because it only oscillates between the energy provider and hooked up load. Due to it more current flows through the grid than what we actually need for the real power demand and as you might know; for a bigger current flow we need thicker wires, so that things do not get terrible inefficient and
• 03:30 - 04:00 hot and that of course costs lots of money. So keeping the reactive power close to zero is our goal here meaning that apparent power should equal the real power. And in the heat gun example we started with we can actually see such a behaviour that real power equals apparent power meaning it is definitely possible which brings us to the question how such reactive power comes to be?
• 04:00 - 04:30 The most popular examples for that are simply a motor and a capacitive power supply that you can sometimes find in LED lights. Both of them create quite a bit of reactive power in comparison to their real power and the root of all evil for that is like I teased at the beginning their current flow. The power supply ones leads in comparison to the mains voltage and the one from the motor lags in comparison. The reason for that are of course the electrical properties of the capacitor for the power
• 04:30 - 05:00 supply and the inductance for the motor coils. But feel free to watch my previous videos about those topics here so that I can keep the rest of this video short and sweet. Because in a nutshell such phase shifts do create reactive power. And the simple fix here is to add inductance to the capacitance and vice versa capacitance to the inductance to get rid of the phase shift and thus reduce the reactive power and
• 05:00 - 05:30 get a power factor of almost one. By the way the Power Factor is simply the real power divided by the apparent power and thus one means real power equals apparent power which is what we are after. Now like I said; one solution is adding capacitance or inductance to the power grid to decrease the phase shift and that is actually the first type of a power factor correction circuit and it is called a passive one.
• 05:30 - 06:00 Of course, there is also an active one that I already presented to you at the start. And to understand why we need it, let's go back to the current draw of a common power supply I found in my shelf. As you can see the more DC current I draw from its output, the bigger the current pulse on the input near the peak of the mains voltage gets. And by doing my usual measurements next, we
• 06:00 - 06:30 can see that this current draw creates kind of a lot of reactive power which is easily noticeable through the low power factor. But there is no phase shift, so how does that work? Well, the problem here is that this current waveform can be depicted as a sum of lots of current waveforms with different frequencies. Most importantly of course is the 50Hz fundamental frequency which is our mains voltage frequency
• 06:30 - 07:00 and it obviously does not feature a phase shift. But then there are also 150Hz, 250Hz, 350Hz and so on parts which are called third, fifth, seventh and so on current harmonics and they do kind of feature a phase shift that creates the reactive power. By using my oscilloscope we can actually see how much they matter in comparison to the fundamental 50Hz frequency and let's just
• 07:00 - 07:30 say that they are pretty dominant on the screen here. So what we can do to fix this problem is basically convert this small current pulse to an even sinusoidal one. And like I said before a circuit that can do that is an active PFC for which I looked for on Mouser Electronics. And I found a promising looking IC that only requires a few external components to function.
• 07:30 - 08:00 But before creating a whole PCB for it which requires lots of time, I firstly wanted to do some initial tests with a similar IC, for which Mouser luckily offered a development board. After powering its low voltage side with my lab bench power supply, I next prepared a proper mains voltage wire for it and this break might be a good opportunity to state that working with all the mains voltage show in in this video can be dangerous and you
• 08:00 - 08:30 should only do that if you are a professional. OK, with that out of the way I plugged the circuit into mains voltage and was very happy to find out that nothing exploded. On its output I measured a voltage of around 400V DC which means the circuit works correctly. And before I start explaining here why this high voltage and how it is made and whatnot; let's rather keep it practical and crack open the power supply that came with the horrible
• 08:30 - 09:00 current draw. After removing its full bridge rectifier, I simply connected the output of the PFC to the input of the power supply and by once again plugging in mains voltage, nothing blew up and the power supply seems to work correctly as well. This time though the input current does follow the mains voltage shape a lot more when drawing more current on the output.
• 09:00 - 09:30 That not only means that the current harmonics are mostly gone, but also that the reactive power of the system decreased while the power factor increased, awesome. I think you can see the difference with and without a PFC pretty clearly in this chart here which now brings us to the question how such an active PFC pulls this off? Well, in a nutshell it does so by increasing the changing mains input voltage into a constant
• 09:30 - 10:00 higher DC voltage that the power supply then uses; because yes, an active PFC is basically just a glorified boost converter. You see the problem of normal AC to DC power supplies is that they only draw current near the voltage peak of the mains voltage because that is when the utilized capacitors voltage drops beneath the input voltage and thus can get charged up again. But by supplying a constant boosted voltage
• 10:00 - 10:30 this problem basically disappears. Of course creating such a stable boosted DC voltage from a varying input voltage is not that easy because you need to monitor the input and output voltage as well as the flowing current and then turn on or off the boost converters MOSFET switch accordingly so that always the right amount of energy gets transferred to the output. When having a look at our practical example
• 10:30 - 11:00 than the MOSFETs switching pattern looks something like with a bigger duty cycle at low input voltages and a smaller duty cycle at higher input voltage which corresponds with the theory. So all in all such active PFCs are pretty awesome. And considering that there are already regulations in place that limit the created current harmonics from appliances, they will sooner or later become mandatory.
• 11:00 - 11:30 So if you are shopping for a new beefy power supply, maybe next time consider getting one with a built in PFC. With that being said I hope you enjoyed this video and learned something new. As always don't forget to like, share, subscribe and hit the notification bell. Stay creative and I will see you next time.