Published: August 18, 2025
Today, our lives are surrounded by so many electronic products. The efficient conversion of electricity from your home’s electrical outlets and batteries is essential for the operation of electronic products. This electricity conversion is performed efficiently by converters, also known as switching regulators. There are several types of converters, including DC-to-DC (direct current, hereafter DC/DC) and AC-to-DC (alternating current, hereafter AC/DC).
In this two-part blog series, we will explain a DC/DC converter in an easy-to-understand way.
In this first blog post, we will focus on a buck DC/DC converter, also known as a step-down converter, which is a common type of DC/DC converter. We will briefly explain its configurations, principles, and features. These features include various control methods for generating waveforms, such as pulse-width modulation (PWM) and pulse-frequency modulation (PFM). We will also discuss the differences between rectification methods, such as synchronous and diode rectification.
What Is a DC/DC Converter (DC/DC Switching Regulator)?
Types of DC/DC Converters
Features of a Widely Used Buck DC/DC Converter (DC/DC Switching Regulator)
What Are the Configurations and Operating Principles of a Buck DC/DC Converter (DC/DC Switching Regulator)?
What Are PWM and PFM Controls?
What Are Synchronous and Diode Rectifications?
Various Topologies, a Feature of a DC/DC Converter (DC/DC Switching Regulator)
A DC/DC converter is also commonly referred to as DC/DC switching regulators. Before explaining a DC/DC converter, let us briefly introduce the different types of power management ICs. (See Figure 1.)
There are various types of power management ICs. They can be divided into two categories: linear and switching regulators. Linear regulators, such as low-dropout (LDO) regulators, control their transistors in a linear (analog) manner to regulate the output voltage. Switching regulators, such as DC/DC converters, output a constant voltage by turning switches on and off.
Switching regulators include AC/DC converters, which convert AC voltage (such as those used in households) into DC voltage, as well as DC/DC converters, which generate DC voltages, such as 5V and 3.3V, after AC/DC conversion. They also include DC/DC controllers*1.
*1 A DC/DC controller does not have built-in driver field-effect transistors (FETs); instead, it controls external FETs. In contrast, DC/DC converters, or DC/DC switching regulators, have built-in driver field-effect transistors (FETs).
Figure 1. Types of power management ICs and DC/DC converters (shown in blue)
What types of DC/DC converters are there?
They can be divided in various ways, but when classified by the type of external components used, they can be broadly classified into inductor type, transformer type, capacitor type, etc.
This type of DC/DC converter uses an inductor, or coil, to store and release energy in order to convert voltage. They can be classified by their various methods.
Table 1. Various methods of inductor type
| Conversion Methods | Several methods of energy conversion can be used to convert DC voltage to different DC voltages. The methods include buck (step-down), boost (step-up), inverting, and buck-boost (step-down and step-up). |
| Rectification Methods | The methods include synchronous and nonsynchronous rectification. |
| Control Methods | These refer to techniques for controlling the on and off timing (pulse) of switching elements. The methods include pulse-width modulation (PWM), forced PWM, and pulse-frequency modulation (PFM). |
| Circuit Methods | These refer to control methods other than the pulse control mentioned above. The methods include feedback loop control, which includes voltage mode, current mode, and COT control. |
A transformer type, also known as an isolated type, is a DC/DC converter that completely separates the electrical connections between the input and output. There are three main methods of transformer types.
Table 2. Methods of transformer type
| Flyback Method | This method features a compact and simple structure. During the switching operation, energy is stored in a transformer and released to the output side, thereby converting voltage. This method is primarily used in low-power, low-cost designs and is commonly found in isolated power supplies for home appliances and small electronic products. |
| Forward Method | During the switching operation, this method transmits energy directly to the output side through a transformer. An output filter then stabilizes the power supply. This method is more efficient than flyback method and is ideal for applications such as communication and industrial equipment. |
| Push-Pull Method | This method uses two switching elements that operate alternately to drive a transformer. Since both directions of the transformer can be used, high efficiency and output power can be achieved. This method is used in large industrial equipment and in situations that require high power. It is particularly well-suited for high-efficiency systems. |
A capacitor type, also called a switched capacitor, is an electronic circuit that, like a resistor, limits current or voltage by combining capacitors and switches. The most common power management circuit of this type is called a charge pump.
Table 3. Charge pump types and features
| Step-Down Charge Pump | Series-connected capacitors are charged by the input voltage. Then, they are reconfigured in parallel, which divides the voltage. Switching between these configurations produces a lower output voltage. |
| Step-Up Charge Pump | Parallel-connected capacitors are charged by the input voltage. Then, they are reconfigured in series, which adds the voltage. Switching between these configurations produces a higher output voltage. |
| Inverting Charge Pump | Capacitors are charged by the input voltage. Then, they are reconfigured in reverse, which inverts the voltage. Switching between these configurations produces an inverting output voltage. |
This blog will focus on inductor-type DC/DC converters among the various types of DC/DC converters.
As mentioned above, DC/DC converters are regulators that use a switching method to convert a DC voltage to a constant DC voltage, also known as DC/DC switching regulators. The most commonly used of these is generally a buck DC/DC converter, which stably outputs a voltage lower than the input voltage. A buck DC/DC converter has several advantages over a linear regulator which also operates in buck mode.
- High efficiency
- Large current flow
- Low heat generation
etc.
Figure 2. Features of a DC/DC converter
Why are these advantages associated with a DC/DC converter? We will explain its configurations and operating principles in the next section.
We will use a buck DC/DC converter as an example.
Figure 3 shows a basic circuit configuration. It consists of two switching elements (hereafter referred to as “switches”), an inductor (or a coil), and a capacitor.
Figure 3. Circuit diagram of a buck DC/DC converter
Figure 4 shows how the operation works.
In response to the input voltage (the left side of Figure 4), switches called high-side and low-side are controlled and turn on and off alternately, resulting in a pulse waveform (center of Figure 4, “Output Voltage of Switches”).
The waveform is smoothed*2 by an LC circuit, or low-pass filter, consisting of an inductor (L) and a capacitor (C). This produces a constant voltage on the output side (right side of Figure 4, “Output Voltage”). Figure 3 shows an LC circuit enclosed by the dashed line.
*2 Smoothing is achieved with an LC circuit. The inductor (L) and capacitor (C) play the following roles:
The inductor (L) works to slow down the change in current, and when a pulsed current passes through the inductor, the rapid change in current (ripple) is suppressed and the output current is smoothed.
The capacitor (C) stores an electric charge to suppress voltage fluctuations. Thus, the output voltage is stabilized by the current flowing from the inductor into the capacitor.
Figure 4. Voltage waveforms of a buck DC/DC converter
The key to regulating the output voltage is the ratio of the time that the high-side switch is on to the total time. This ratio is called a duty cycle.
The formula for duty cycle is as follows:
Duty cycle = Ton / (Ton + Toff),
where Ton is the duration that the high-side switch is on, and Toff is the duration that the low-side switch is on. The total time of Ton and Toff is considered one period.
The larger the duty cycle (i.e., the longer the high-side switch on time), the higher the output voltage. Conversely, the smaller the duty cycle (i.e., the shorter the high-side switch on time), the lower the output voltage. Essentially, the output voltage (Vout) remains constant if the input voltage (Vin) and duty cycle are determined.
Vout = Vin × duty cycle
Voltage and current are supplied from the input side only while the high-side switch is on. When the high-side switch is off, the supply of voltage and current stops. The inductor plays a role in supplying current when the high-side switch is off.
Inductors play a crucial role in a DC/DC converter by storing and releasing energy. This process is illustrated in Figures 5 and 6, which show Steps 1 and 2, respectively.
Figure 5 (Step 1) shows that the high-side switch is on, and the low-side switch is off. The load connected to the output side is supplied with the required current from the input side (Vin) through the inductor. As the current flows through the inductor, energy is stored as magnetic energy.
Figure 5. Step 1: Energy storage when the high-side switch is on and the low-side switch is off
Figure 6 (Step 2) shows that the high-side switch is off, and the low-side switch is on. Although the high-side switch turns off, the inductor tries to maintain the current flow. This releases the inductor’s stored energy as a current to the output side. Thus, a current is provided to the output side even when the high-side switch is off.
Figure 6. Step 2: Energy release when the high-side switch is off and the low-side switch is on
The above illustrates the operating principles of a buck DC/DC converter.
Next, we will take a closer look at two control methods that are representative features of a DC/DC converter: PWM and PFM.
Click here to see our lineup of Buck DC/DC converters (DC/DC switching regulators).
As mentioned above, one feature of a DC/DC converter is adjusting the voltage based on the ratio of the high-side switch on time (hereafter, on time). There are two ways to adjust the ratio.
One approach is to adjust the on time (pulse width) within one period while keeping the on and off switching period (i.e., switching frequency) constant. Another approach is to keep the on (or off) time constant and adjust the on and off switching period (i.e., switching frequency). The former is called PWM control, and the latter is called PFM control.
PWM stands for pulse-width modulation.
As mentioned above, the on time (pulse width) within one period is adjusted while keeping the switching frequency constant.
Because the switching frequency remains constant in PWM control, it is easy to suppress the noise that occurs when the switches turn on and off. PWM control also features a high level of responsiveness to load current fluctuations. However, PWM control is less efficient at light loads than that of PWM control.
Figure 7. Pulse-width modulation (PWM) method using a constant switching period and adjustable on time
On the other hand, PFM stands for pulse-frequency modulation.
In PFM control, the switching frequency is adjusted according to the operating conditions of the load device. Therefore, the switching frequency is lower at light loads, which results in lower switching losses. On the other hand, it has a disadvantage meaning that taking countermeasures against noise is difficult because the frequency of switching noise changes depending on changes in the switching frequency.
Figure 8. Pulse-frequency modulation (PFM) method using a constant on time (or off-time) and adjustable switching frequency
In recent years, some products that can automatically change their control methods have emerged. These products switch between PWM control for normal operation and PFM control for light loads. In any case, the important thing is to define the operating conditions of your application and select a DC/DC converter with an appropriate switching method.
Click here for buck DC/DC converters that can automatically change between PWM and pulse-PFM control.
A DC/DC converter has another feature that includes two methods: synchronous rectification and diode rectification, also known as nonsynchronous rectification.
Figure 3 in the section “What Are the Configuration and Operating Principles of a Buck DC-DC Converter (DC-DC Switching Regulator)?” illustrates a circuit diagram of a DC/DC converter with synchronous rectification. The high-side and low-side switches shown in Figure 3 are implemented using transistors, such as field effect transistors (FETs). The high-side and low-side switches turn on and off alternately with a switch control circuit. This method is called synchronous rectification because the timing of when the high-side and low-side switches turn on and off is synchronized.
On the other hand, Figure 9 shows an example of a buck DC/DC converter with diode rectification. Here, the low-side switch from Figure 3 is replaced with a diode that performs the same function. The diode rectification method is relatively easy to control because it only requires consideration of when a single switch turns on or off. However, the diode itself consumes power, which is disadvantage in terms of power conversion efficiency. Therefore, a Schottky barrier diode, which has a low forward voltage (Vf) drop, is used to minimize power consumption when the diode is on.
Figure 9. A buck DC/DC converter with diode rectification method
At first glance, one might think the synchronous rectification method has more advantages since it doesn’t require external components. However, this method also has disadvantages.
Specifically, it requires an additional circuit to control the timing of the two switches turning on and off. This circuit tends to be more expensive than the diode rectification method.
Turning on the high-side and low-side switches simultaneously creates a short-circuit path from the input to ground. The resulting current could cause a DC/DC converter to destroy itself. Therefore, an additional control circuit is needed to prevent this risk.
Therefore, it is necessary to evaluate them based on various aspects, such as efficiency and cost, and use them accordingly.
What is the difference between diode rectification and synchronous rectification?
So far, we have discussed several features of a buck DC/DC converter. This is the end of the first part.
The main feature that distinguishes a DC/DC converter from a linear regulator is that a DC/DC converter has various topologies*3, meaning they can operate in buck, boost, buck-boost, and inverting modes. In contrast, a linear regulator can only operate in buck mode.
*3 In electric circuits, “topology” refers to the state of the connections between components. In this context, however, the term refers to the type of circuit operation resulting from different connection states of the circuit.
In the next post, Part 2, we will discuss operation modes other than buck, such as boost, inverting, and buck-boost. We will also compare a DC/DC converter and a linear regulator, as well as discuss its various protection functions.
Click here for our lineup of our DC/DC converters (DC/DC switching regulators).
Note: You’ll find it around the middle of the page.