Buck circuit: Structure, operating principle, and application

Buck circuits are widely used in various electrical devices. So what is the structure of the Buck circuit and its operating principle? Follow the article below to find out!

What is the Buck circuit?

Buck circuit, low voltage Buck circuit, or Buck converter, is the common name used to refer to a common type of DC-DC converter circuit today. In the basic Buck circuit, there will be four basic electronic components: a diode, an electronic switch, a coil, and a capacitor.
This circuit is used to convert high voltage to low voltage extremely efficiently. At the same time, the Buck circuit also helps convert energy, prolongs battery life, reduces heat generation during operation, and allows for the construction of smaller utilities.

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Structure

The construction of the Buck circuit is very simple, with the MOSFETs turning on and off. There will be a control chip in the Buck circuit that uses a closed feedback loop to regulate the output voltage. In the Buck circuit, the DC transfer function is related to the input voltage, output voltage, and duty cycle of the Buck circuit.

In the Buck circuit, there are also capacitors and inductors, which are connected together to form a low-pass filter that smooths the MOSFET switching operation and makes the DC voltage smoother and more stable.

The formula for calculating the Buck circuit is as follows:

Vout = Vin * EASY

In there:

• Vout is a symbol representing the output voltage of the circuit.
• Vin is the symbol representing the input voltage of the circuit.
• D is the duty cycle or percentage of the time the MOSFET is turned on when the circuit is running.

Buck circuits also have another variant called synchronous buck circuits. The structure will be more different than the usual Buck circuit; that is, the MOSFET will be replaced by a DIODE, making the circuit able to transmit 2-way signals more easily. If you let the Buck circuit run in reverse, it will become a Boost circuit, and then you just need to add a converter IC.

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Working principle

Buck circuits work on the principle of pulse hashing, that is, using circuit keys that implement electronic switching MOSFETs. It is also possible to use a BJT to connect the load to the source for a certain period of time according to cycle T. At this time, the output voltage of the circuit will change according to the period T and the real-time of switching the switch.

The requirement when operating a Buck circuit is that the DC output voltage must always be lower than the DC input voltage. The output voltage can be taken directly from the AC source through any DC supply, for example, a diode bridge, filter capacitor,… Specifically, the principle of operation of the Buck circuit is as follows:

• Bringing current through semiconductor electronic components and inductors, electric coils perform charging for the capacitor, and when charging is complete, it will maintain the current through the load.
• The current through the coil and the charging current into the capacitor will increase slowly, and at the same time, the output voltage on the load will also gradually increase. At this point, the diode will not conduct electricity because it is reverse-biased.
• When the current through the load is turned off, the diode will automatically program the current through the main load, ensuring the protection of semiconductor components from damage due to reverse voltage when the current is cut off and limiting the situation of semiconductor components dying as soon as possible. Reverse voltage is generated by the inductor and the power supply increases.

Application

USB On The Go

The Buck circuit is used in USB On The Go. This is a device that draws power from the USB port on the phone and allows you to connect the keyboard, mouse, and other peripherals to the smartphone.

In the USB On The Go structure, the Buck circuit plays the role of regulating power transmission in both directions. When you leave your phone plugged into the charger, the circuit acts like a regular switch to charge the lithium battery in the phone. If you leave a peripheral plugged in, the Buck circuit will turn into a Boost circuit to generate 5V from the lithium battery.

POE adapter for PCs and laptops

A POL converter is also known as a voltage regulator module or load point converter. Usually, PC or laptop processors run at very low voltages, so the application of Buck circuits in POL converters will help transfer power more efficiently to higher current loads.

Battery charger

Usually, when using a fast battery charger, it inevitably heats up the plugged-in devices. To limit the heating of the device when charging, manufacturers have applied Buck circuits in battery chargers. The Buck circuit will adjust the voltage, reducing heat generation during the charging process of the phone battery.

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Above are the structure and operating principles of the Buck circuit. Hopefully, through this article, people will have a better understanding of this type of circuit. If you have any further questions, do not hesitate to contact a reputable distributor of soldering materials and electronic components, Thetech, for answers!