Zero Background Knowledge Required: This will help you understand Buck and Boost Converter
A technical article for non-technical readers, and engineering-to-be students
If you have a background in electrical engineering or power electronics, you most definitely heard about the power converters. Even if you do not have such experience, you must have seen different voltage levels of battery, i.e. 1.5V AA battery or 9V battery, and voltage ratings of electronics.
Why are there so many different voltage levels?
The different electronics operate at various voltage levels. For example, anything has a USB cable, like an iPhone charger, Kindle charger, or USB light. They operate at 5V. Anything powered by AA or AAA batteries, like RC cars and remote controls. They operate at 3V or 6V depending on the number of batteries required.
Just like city roads, paths are always intertwined with intersections. A voltage conversion methodology for different voltage level electronics is a must.
The power converter is the magic behind translating one voltage to another. Two basic topologies are the buck converter for bringing down voltage and the boost converter for boosting up the voltage.
HEY! Before you close this article and say, “oh, this is one of those technical articles full of jargon, and only electrical engineers could understand. I am bored”.
I want you to know: You are wrong, and I promise you this would be a different approach to technical articles.
I often got frustrated by technical abbreviations and knowledge assumptions during my study of engineering. From time to time, on a textbook or from a class, I experienced countless times where the knowledge was assumed to be easily comprehensible and was not explained in regular English. Furthermore, the curriculum goes on and introducing more sophisticated concepts, making the subject increasingly confusing.
It’s time to try something different: no abbreviation nor ambiguous technical jargon. Let me hold your hand and walk you through some incredible circuits on modern personal electronics. In a way, anyone, with or without an electronics background, would understand.
Terminology Converting
The buck converter and the boost converter can shift voltage level up and down. How do they work? To understand what these are, let’s draw an intuitive picture by substituting a subject we can’t see, into something we can see and use every day: substitute electrons with water particles by imaging the electrical system as a water pumping system. That is, let’s picture electrical current as water current.
Here is when I slap a table onto you for quick referencing before I keep talking about it. The following table is to demonstrate how the electrical system translates into our water analogy.
Here is an excellent video explaining what is the electrical voltage. I suggest you check out more video create by this channel and learn more about the basic of electronics:
Critical Parts
Three essential parts play significant roles in both the buck and the boost converter. Let’s have a basic understanding of those before we dive deeper. Below is a buck converter simplified circuit diagram to pleasing your eyes and act as a reference to the following section.
Input Voltage Source
First, you have the voltage source “Vs” is your water source. This will provide you with a constant pressure of water supply. Ideally, it would not drop pressure no matter how much water you demand it to give. As you might know, nothing is ideal in this world. In circuitry, if the source is a battery, with a discharge of current, its voltage will drop as well. The existing battery technology still can’t consume its mass to keep generating electrons. Therefore, its voltage will drop unavoidably when discharged.
Same as our water system, the pressure of the water depends on how much water you compressed together. More water compress in a container, more pressure builds up in that container. Naturally, when you release those compressed water, the pressure will drop. To keep the pressure in the tank, the outflow amount of water has to equal to the inflow amount.
But for now, let’s keep it simple and say the source can provide infinite water without losing its pressure.
Output Capacitors and Load
The electrical load could be anything like a light bulb or a stove. In our analogy, it would be a single house or an industrial building. It needs to be operated at a specific pressure. It could be less pressure than our pump pressure, or it could be higher. The water consumer only needs or cares about two things: constant water pressure and enough water coming out when it is required.
To maintain the pressure and throughput, we need a reservoir water tank big enough to provide sufficient water when is required, making the pressure drop unnoticeable to the consumer. That is what an output capacitor “C” does.
The Star of the Show: The reluctant Inductor
The inductor is the most crucial part of the power converter. To say it is the star of the show would not be exaggerating.
This is a device reluctant to any change (of electrical current). Its stubbiness involved with energy conversion between electrical current and magnetic fields. It just doesn’t like to change.
In our water analogy, we can see the inductor as the inertia of the water. A moving body of water cannot be stopped immediately. It will keep going toward its original direction. Vice versa, It would like to stay at the same place when starting from stationary. This is also known as Newton’s first law of motion.
All the power converters use this property to achieve a higher voltage or maintain a lower voltage level. We will talk about more about how it works in the following section.
The Story of a Water Supply Company
Let us be entrepreneurial and put our analogy in practice by opening a water supply company!
First, let’s figure out how to deliver water to different customers using buck and boost converter topologies.
Our new customers want us to supply their common household water. However, our pump station provides a higher water pressure than our customers can handle. What infrastructure (circuit) can we implement to meet our customers’ requirements? The answer is a buck converter.
Buck converter
As we discussed earlier and showed in the previous diagram is a simplified buck converter. The two components on the right are the load and the output capacitor. The component on the left is the voltage source. Now, there are two additional parts in this buck converter. One is the switch, and one is a diode. But before we explain how they play in our water pumping business, let us go through how are we bring down the water pressure to our customers.
We have a water reservoir tank “C”, which provides water to our customers when there is a water usage surge. We cannot directly connect our supply to this tank “C”. If we do that, the tank “C” will have the same pressure as our supply, and our customer’s faucets would explode.
Here we need a way to reduce the pressure while still maintain the output water flow. A combination of inductor and switch would serve our cause.
Remember, the inductor would be a representation of inertia of the water: It will maintain the flow of the water or maintain the stillness of the water. Once we connect our pump supply to the inductor, the other side (customer side) does not instantaneously experience the water pressure. The inductor will provide buffered water flow and let the customer side pressure increase slowly.
However, with time, once water flow becomes constant, the inductor would become a regular pipe, and the customer will eventually reach the same pressure of our supply. So we are not done yet. We still haven’t brought down the pressure.
Switch
By adding a switch to control the ON and OFF of our “Vs” water supply to the system, we can reduce the pressure with additional help from our inductor. Instead of having our supply connects to the system all the time, we connect it for some time and then off. This is a similar concept compares to Pulse Width Modulation (PWM) control.
However, In this case, we turn ON and OFF of the water source to regulate the amount of water going through the inductor. Due to the reluctance nature of the inductor, the consumer side will see a lower average pressure.
Diode
As you can see, there is a Diode D. What is a diode, and why is that there? Remember, we are saying the inductor represents water inertia. Once we cut off water supply “Vs”, the water still trying to move forward in the system. But, there is no more water pushing behind them. But it is still moving, so what’s behind them now? Nothing! We have created a vacuum near the switch.
This phenomenon is both dangerous in water pipes and in electrical systems. In a pipe system, it will cause atmosphere pressure pushed onto the pipe and damage it. In the electrical system, the voltage on the left side of the inductor, near the switch will drop significantly and cause damage to our switch.
The diode is a one-way valve. It only allows water to go from one way, not the other. Therefore, when the switch is off while the inductor is still moving water forward, the diode starts to work, providing extra water from the return pipes to maintains pressure in the piping system. That is why the diode is there.
Please note, here I assume are water analogy is a close system. The water gets circulated within the system. Therefore, not all water is used on the consumer side. Some of them will come back to the source. Return pipes in our analogy are equal to the ground in the electrical circuit. For the definition of ground in the electrical system, please see here.
To maintain the water pressure while providing enough water flow into our customer’s home, combine the switch using PWM with the inductor, we can create a dynamic system that will make our customers happy and willing to pay.
Boost Converter
Now, what if we need to provide water supply to a factory where higher water pressure is required than our supply? We can then use the same parts from our buck converter but in a different order to increase the water pressure.
Now we put the inductor near our supply and the diode behind a switch connecting to the ground. The output tank “C” is still at its original position. This topology is called the boost converter.
During Turn-On state, we let the water start to flow through an inductor. When there is a lot of water flowing through, we turn off the switch. Remember, the inductor is reluctant to change. Therefore, when the switch is off, it will push the already flowing water to the diode. The diode will allow water to keep going forward and pushing water in the output water tank “C”. The inertia of water will eventually die down, and water flow would be zero. At this point, water tank “C” and supply will have the same pressure. Again, this is an extreme case. We need to take action before this happens.
Therefore, on the next cycle, we turn on the switch again and start let the water flowing speed build up again. Due to the diode blocking water flow backward, our water tank “C” is still providing water to the output and pressure would dropping a little (if the water tank “C” is significantly bigger than the output demand). Once again, we have a lot of water flowing through the inductor. Now we open the switch and let those water flash into the capacitor. With more and more water pumping to the water tank “C”, the pressure will build up again.
Naturally, water flows from high pressure to low pressure. However, since we have a diode as a one-way valve, which prevents water from flow backward, the pressure on the water tank “C” will only become higher than the supply due to water keeps rushing in from the inductor.
With the combination of buck and boost converter, our water supply company has income both from residential and industrial customers!
Last But Not the Least
There is a combination of both buck and boost converter, which require a more sophisticated control method. You can learn this here.
Of Course, another type of power converter that dominates household electronics: the Flyback converter. I can say this: without the flyback converter, we would not have so many personal electronics nowadays. From phone laptop charging to household appliances, flyback is the cornerstone of the boom of electrical devices. I will have another article coming up to talk about what I learn from one of my IoT projects. It will address specifically about flyback converter design.
Conclusion
Hopefully, this article helps you understand more intuitively about buck and boost converter. Please be mindful, this article solely introduced a basic level of knowledge in power converters. If you are genuinely intrigued by the topic I have presented, I encourage you to research more on electrical fundamentals to strengthen your understanding. I have an excellent video for you. In this video, it shows a fantastic animation of how buck and boost converter works. I recommend you go check it out.
Originally published at https://www.linkedin.com.
