DC-DC Converter

DC/DC converter is a switching power supply chip, which refers to the use of the characteristics of capacitors and inductors to store energy, through the controlled switch (MOSFET, etc.) to carry out high-frequency switching action, the input electrical energy is stored in capacitors (inductors), and then when the switch is disconnected, the electrical energy is released to the load to provide energy. Its ability to output power or voltage is related to the duty cycle (the ratio of the time the switch is on to the entire period of the switch). Switching power supplies can be used for boosting and bucking.

Simply put, DC-DC converter is an electronic circuit that converts one level of direct current (DC) voltage into another. This transformation can involve stepping up (boosting), stepping down (buck), or inverting the voltage level depending on application needs.

DC-DC Converter Working Principle

The output voltage is compared with the reference voltage through a voltage divider resistor, thus creating a feedback. When the output voltage decreases and falls below the reference voltage, the comparator output flips and triggers the oscillator circuit to start working. The oscillator outputs a fixed time pulse, which is used to control the conduction of the MOS tube. Conversely, the MOS tube will be cut off. The on-state is controlled by the oscillator and the cut-off time depends on the load. In this way, the output voltage can be controlled.

Here’s a simplified explanation of how they work:

Core Process:

• High-speed Switching: A semiconductor switch (like a MOSFET) rapidly turns on and off using PWM (Pulse Width Modulation).
• Energy Storage: When the switch is on, energy is stored in components like inductors or capacitors.
• Energy Transfer & Output Filtering: When the switch is off, stored energy is transferred to the load and output is smoothed via capacitors.

This switching method allows efficient energy conversion (typically >85%) and supports compact designs with minimal heat dissipation compared to linear regulators.

Types of DC-DC Converters

• Buck Converter: Also known as a step-down converter, the buck converter reduces a higher input voltage to a lower output voltage. It maintains the same polarity between input and output and is widely used due to its high efficiency and simple topology. This type is ideal for applications where electronic components require a lower voltage than the main power source, such as microcontrollers, processors, and digital circuits.
• Boost Converter: The boost converter, or step-up converter, increases the input voltage to a higher output voltage while preserving polarity. It is commonly used in scenarios where the available input voltage is too low for the load, such as in battery-powered systems, LED drivers, or solar-powered devices. Boost converters are compact and efficient, but their output current is typically lower than the input current.
• Buck-Boost Converter: This converter can both step up and step down the input voltage, making it highly versatile. It is particularly useful when the input voltage can be both above and below the desired output voltage. Depending on the topology, the output polarity can be the same or inverted. Buck-boost converters are common in battery-operated devices where the battery voltage varies significantly during discharge.
• SEPIC Converter: The Single-Ended Primary Inductance Converter (SEPIC) allows both step-up and step-down conversion with the same output polarity as the input. It offers improved voltage regulation and lower output ripple, which makes it suitable for noise-sensitive applications. SEPIC converters are often found in automotive systems and consumer electronics that require a stable voltage supply across a wide input range.
• Cuk Converter: The Cuk converter also supports both voltage step-up and step-down functionality, but with an inverted output polarity. One of its key advantages is the continuous current at both the input and output, which reduces electromagnetic interference (EMI). It is commonly used in analog and audio systems where clean power delivery is important, although its design is more complex than other non-isolated converters.
• Flyback Converter: Flyback converters are isolated DC-DC converters that can provide either higher or lower output voltages relative to the input, with the added benefit of galvanic isolation. They are suitable for low to medium power applications and can generate multiple output voltages from a single input. This topology is often used in industrial power supplies, AC-DC adapters, and low-cost isolated systems.
• Forward Converter: Similar to the flyback converter but designed for higher power applications, the forward converter also provides electrical isolation between input and output. It offers better efficiency and faster response to load changes. Forward converters are often used in telecommunications and industrial applications where power levels are moderate to high.
• Push-Pull Converter: The push-pull converter is an isolated topology that uses two transistors switching alternately, providing symmetrical power delivery. It is capable of delivering higher power and is more efficient than single-ended converters at moderate power levels. Push-pull converters are used in applications such as communication equipment, medical power supplies, and onboard DC-DC systems.
• Half-Bridge / Full-Bridge Converters: These high-efficiency, high-power isolated topologies are used in demanding environments such as server power supplies, electric vehicle (EV) chargers, and power inverters. They provide balanced power delivery and are suitable for converting high voltages at high frequencies with minimal loss. While complex and costly, they are essential in systems requiring precision and power density.

Comparison of DC-DC Converter Types

How to Select a DC-DC Converter

• Input Voltage Range: Start by identifying the minimum and maximum input voltages your system will encounter. A suitable DC-DC converter must be able to operate reliably across this entire range. For example, if your input source is a battery that varies from 9V to 16V, the converter should function without issues throughout that range. Choosing a converter with a slightly wider tolerance adds robustness against voltage dips or spikes.
• Output Voltage and Current Requirements: Define the exact voltage and current your load needs. This includes both the nominal values and possible peak demands. Some applications require tight voltage regulation, especially in digital electronics, while others—such as motors—might tolerate minor fluctuations. Make sure the selected converter can supply the maximum required current without exceeding thermal or electrical limits.
• Efficiency: Efficiency is critical, especially in battery-powered or thermally constrained systems. Higher efficiency translates into less heat generation and longer battery life. Switching converters typically offer efficiencies ranging from 85% to over 95%, depending on the topology and load. Evaluate efficiency under your specific load conditions—not just at peak efficiency points.
• Topology Selection: Choose the appropriate converter type (Buck, Boost, Buck-Boost, etc.) based on the relationship between input and output voltage. If input is always higher than output, a buck converter suffices. If input is lower, choose boost. For fluctuating input or complex requirements, buck-boost or SEPIC may be better suited. Isolation needs also affect topology: flyback and forward converters are common isolated types.
• Isolation Requirements: For safety-critical systems, medical devices, or noisy industrial environments, isolation between input and output is often required. Isolated converters like flyback or forward topologies provide this separation, protecting users and sensitive circuits from faults or surges on the input side.
• Control Features and Protections: Modern converters offer various features like soft start, enable/disable pins, under-voltage lockout (UVLO), over-current protection (OCP), and thermal shutdown. Choose a converter that offers the right balance of functionality and cost, based on the complexity and criticality of your application.

Application