DC to DC Buck converter working principle

This is a DC to DC Buck converter working principle. We often use it as a step-down DC to DC converter circuit. Because it is a switching mode power supply.

It works by switching on and off. So it can get a much higher power efficiency than a linear power supply.


It steps down the input voltage from high to a low voltage output. While it will step up output current to load.

DC to DC Buck converter working principle

So, the switch mode power supply is very popular. Because it is the power-saving circuit.

Learn more: How it works and types

Do you think that a switching supply is hard? especially beginner or an electronics hobbyist.


But wait, try to read this. It may change your mind.

We can try to play or real use. We do not need to use expensive parts or too complex. You already have the pieces of equipment exactly.

The main principle of Buck DC to DC converter

See in the simple block diagram. Most DC to DC converters operate as the switching mode power supply. Its input is DC unregulated supply. The output is DC regulated voltage that stable.

Block Diagram of DC to DC Converter

Simply said, the DC to DC converter will change the voltage source. To higher or lower or something else. By the purpose of the designer or our circuit ideas.

When we see a basic buck converter circuit as Figure 2. It is easy to understand:

  • Vin is an input voltage as popular as the United States. And “Uin” for the European country.
  • Vout is an output voltage of the United States. And “Uout” in European countries.

In this circuit, it consists of 3 main components only.

  • S is a switch, in the real circuit, we use a transistor.
  • D is a diode.
  • L is a coil or an indictor.
  • C is a Capacitor.
Basic Buck converter circuit diagram
Basic Buck converter circuit diagram

Figure 2: Buck converter working principle

Figure 2 is a basic buck converter circuit. It powers a certain output voltage. Other converter systems may call that a step-down.

Step by step process

First, the Vin charges into the capacitor until full. Its voltage is the same as the power supply input.

Next, switch closed into the circuit. Therefore the positive voltage to drop across the coil L.


Energy stored in coil

Recommended: Is it hard?  Learn the power supply circuit

The current flow through the coil to increase up in linear rate. While there is energy stored in the coil.

Then, the S opens up. So, the current of L flow to the output capacitor.

And it flows through Diode (D). It makes the voltage drop across the coil L in backward (negative).

Energy stored in the output Capacitor
Energy stored in the output Capacitor

And, the current through the coil reduces in linear. The energy stored at the output capacitor.

When the switch (S) connected to the circuit again. The system started working on the new one. To be able to supply the load continuously.

You may like to learn others

In Practice, It is difficult to control the switch(S). It will make the energy to the output. How to do it?

3 types of DC converter current-mode

Figure 3 Three types of current mode

Note: See example circuits

I see you sleepy. Because reading boring working principles, me too. Sure, we like to see circuit and circuit. We have imagined making a great project, right? But learning is so important. When we learn this, we can do these circuits see below.

  1. DC to DC Buck converter working principle
  2. Switch mode LED driver circuit (Save energy)
  3. USB 5V to 12V DC-DC Step-Up Converter circuit
  4. Simple 12V transistor switching power supply
  5. 1.5V to 5V boost converter circuit for microcomputer
  6. 5V to +/- 12V boost converter circuit or higher using transistor

You should read all for more understanding.

By the way, we continue to learn the principle of a buck DC converter.

In normal principle, the electricity flows in 3 modes. As shown in Figure 3.

  • Continuous mode (CM): When the switch is closed. Then, the current is continuously flowing in the coil. See Figure 3A
  • Discontinuous mode (DM): But if we control times to switch on-off.
  • CM/DM boundary: This mode, the switch turn-on immediately, if a current of coil drop to zero.

There are too many principles to control the switches ON-OFF. But we do not need to use all principles in one working. Because our some project use a few principles only. We do want to know what we learn just one only.


Let’s see a true circuit. To tell the story. It is the best solution. We would like to actually get into the next circuits.

Learn Next: Switch mode LED driver circuit

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