The Importance of Switching Speeds in Transistors
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When it comes to power electronics, the efficiency and speed of transistors are crucial factors to consider. In this article, we'll explore why switching speeds are important and how they impact the performance of transistors.
Why Switching Speeds Matter
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Switching speeds refer to how quickly a transistor can turn on and off. This is particularly important when it comes to power losses. When a transistor switches on, it needs to charge up its gate capacitance, which requires a significant amount of energy. Similarly, when it switches off, it needs to discharge that same capacitance. As the frequency of switching increases, so does the power loss.
To mitigate these power losses, transistors are designed with various features such as small capacitance values and low total gate charge. These design choices enable faster switching speeds, which in turn reduce power losses.
GaN FETs: Faster Switching Speeds
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Recently, Gallium Nitride (GaN) Field-Effect Transistors (FETs) have gained attention for their improved performance over traditional MOSFETs. One of the key advantages of GaN FETs is their faster switching speeds.
To demonstrate this, we built a simple test circuit using a function generator to create a square wave with variable frequency. We connected our oscilloscope probes to the MOSFET and measured its turn-on and turn-off times. The results showed that the turn-on time was around 70ns, while the turn-off time was around 280ns.
When we replaced the MOSFET with a GaN FET, we repeated the measurements and found that the turn-on time decreased to around 30ns, while the turn-off time dropped to around 100ns. This significant reduction in switching speeds is due to the lower total gate charge of GaN FETs.
The Importance of Switching Speeds in Power Supplies
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In a power supply, switching speed is critical for efficiency. A well-designed power supply should aim to minimize power losses by optimizing switching speeds.
To demonstrate this, we built a basic buck converter circuit using both MOSFET and GaN FETs. We compared the input and output powers of both circuits under identical conditions.
The results showed that the GaN FET-based circuit had a slightly lower input power (6.47W) compared to the MOSFET-based circuit (6.67W). This resulted in a higher efficiency (77%) for the GaN FET-based circuit, which is an improvement of 2%.
Conclusion
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In conclusion, switching speeds are crucial for transistors in power electronics. GaN FETs have demonstrated faster switching speeds compared to traditional MOSFETs, leading to improved efficiency and reduced power losses.
While there are more advantages to GaN FETs, such as lower output capacitance and reverse recovery losses, the results of this experiment demonstrate their potential for improving power electronics. As technology continues to evolve, we can expect even more efficient and powerful transistors to emerge.
Stay creative, and I'll see you next time!
WEBVTTKind: captionsLanguage: enSo recently I have been looking for a new power adapter with USB Type-C output because as you might know from one of my previous videos; USB Type-C is awesome. And even though I already own such a power adapter, I wanted another one for simultaneous charging action. What I noticed though while having a closer look at a couple of relatively new products, was that they are advertising with the term GaN which stands for Gallium Nitride. So after doing a bit more research on the internet about this term I realized what all the fuss was about.You see such a power adapter is actually a switched mode power supply and like the name implies it switches a component on and off rapidly with a high frequency in order to basically lower our mains voltage input to a lower voltage output like 5V.The switching component is pretty much always some kind of Field Effect Transistor like for a example a MOSFET about which I already produced 3 videos which you can all binge watch in order to properly understand how this component works. Now traditionally this component was made of silicon but right now the industry is shifting over to Gallium Nitride because it apparently offers many advantages which I will talk about in a couple of minutes. Because in this video I will not only directly compare a GaN power adapter with a more traditional one but I will also test out a proper GaN FET in a switched mode power supply configuration in order to find out whether GaN is truly the way to go for the power electronics industry or whether it is a scam?!Let's get started! This video is sponsored by Keysight University Live. Sign up now for your chance to win some pro-grade test gear – Keysight is giving away over 100 pieces of gear including oscilloscopes, RF, and bench equipment. This online event isn’t just giveaways either, sign up to unlock engineering tips & tricks, and access interviews with industry experts. The event has already kicked off, but it’s not too late! Click the link the description for your chance to win, and subscribe to the Keysight Labs YouTube channel to join the festivities. First off let me tell you that I went with this Kuulaa GaN power adapter that can output 65W which I will compare to my more traditional power adapter that can output 56.5W. So the big question for a comparison is what is most important to consumers when it comes to simply using such power adapters? And my answer is the efficiency which basically describes the relation between how much power the supply outputs and how much power it requires on the input. Of course with a high efficiency you can save money when it comes to your electricity bill which is why I think consumers might be interested in that. To measure the input power I can use my Energy Multimeter which measures and then calculates the real power input without any problems. And to measure the output power I can use such a constant load circuit that basically draws a constant current while measuring the voltage which I then can use to calculate the output power. Of course we will also need such a USB Type C Power Delivery trigger board in order to switch between all available voltage levels of the power adapters. And with the theory out of the way, I continued by spending around 1 hour taking all the measurement at 1A,2A and 3A of output current with all voltage levels for both power supplies. And here you can see the results in this efficiency chart. As you can see the more traditional power adapter outperforms the GaN power adapter at 5V, 9V and half of 12V but then at 15V and 20V the GaN power supply performs better and reaches the best efficiency of both power supplies with almost 90%. So does this test prove that GaN is more efficient? Well, not really since we are comparing two completely different power supply circuits which come with way more components than just the switching component. Those can of course all be different and thus introduce different power losses which means next we should isolate our GaN FET for some more professional testing. And yes I actually opened up the GaN Power adapter in order to see whether it truly uses a GaN FET and to my own surprise it seems like the label of the transistor points me to a more traditional MOSFET.So I am not sure whether this power adapter lied to me or not but nevertheless; next I searched for a proper GaN FET on Mouser and immediately realized that they are damn expensive. That is why I settled for this relatively cheap one and used its maximum current and voltage limits as a guideline in order to look for a more traditional MOSFET with similar ratings and ultimately I went with this one.Now what tests do we have to do to properly compare these two transistors.The first one would be the resistance test meaning how much resistance the Drain Source path comes with when the transistor is fully turned on. For that I simply used 12V at the Gate, let exactly 1A of current flow through the Drain Source path and measured the voltage drop across it. As you can see the MOSFET features 160mV while the GaN FET comes with 119mV which equals a resistance difference of 41mΩ, not bad.That means the GaN FET wastes less power through heat and thus is more efficient, at least according to its resistance. Because when it comes to power losses then it is also very important how fast a transistor can switch on and off meaning how fast its drain source voltage can go down to almost zero and how fast it can go up to the supply voltage.To find that out I came up with this simple test circuit which basically uses a function generator to create a square wave with variable frequency, a gate-drive transformer to drive the gate and the transistor itself with a 16ohm load that will draw a current of roughly 356mA at 12V.And if you are wondering I also had to add an RC snubber to the transistors in order to decrease voltage peaks for the GaN FET to a value of 17V which would otherwise have reached values of around 117V. And with that being said, I set the frequency of the square wave to 500kHz and started by connecting my oscilloscope probes to the MOSFET in order to measure its turn on and off times. It seems like the turn on time is around 70ns while the turn off time is around 280ns. And while I replace the MOSFET with the GaN FET in order to repeat the measurements let me tell you why switching speeds are important. As you probably know the Gate of the Transistor acts like a capacitance which we always have to charge up in order to turn the Transistor on and discharge in order to turn it off. And because of that the capacitance value goes hand in hand with the switching speed. With a small capacitance, we only have to add a small charge to the gate to turn it on which is obviously quicker to do than with a big capacitance and a big charge. And since this charge is also a power loss that obviously increases proportional with the frequency it is best to have a very small value in order to switch fast and save power. And if we have a look in the datasheet of both transistors then we can see that the GaN FET Total Gate Charge is almost 5 times lower than the MOSFET one. So it is no wonder that while measuring the turn on and off times of the GaN FET, that they turned out quite a bit shorter.So far that means that the GaN FET switches faster and features a lower resistance which both means it wastes less power than the MOSFET. But just to be on the safe side and prove my point I built up this basic buck converter circuit which takes a 12V input voltage and converts it down to 5V. Now with the MOSET being used while outputting 5V and 1A on the output, the input power was around 6.67W which equals an efficiency of around 75%And while repeating this exact same setup with the GaN FET, the input power was only around 6.47W which equals an efficiency of around 77%. The difference is of course not very big but it is definitely there and if you build up a switched mode power supply not as horribly constructed as mine then you will notice the difference more easily.Of course there are more advantages of GaN FETs like the lower output capacitance and lower reverse recovery losses due to the non existence of a body diode but if you want to learn more about that I highly recommend checking out some more professional articles about the subject.But nevertheless the verdict of this video is that GaN FETs are certainly not a scam and will improve power electronics slowly over time. And with that being said I hope you enjoyed this video, if so don't forget to like, share, subscribe and hit the notification bell.Stay creative and I will see you next time.
