Buck Converter
Calculate buck converter duty cycle and inductance from input voltage, output voltage, switching frequency, and ripple current. Free DC-DC step-down converter calculator for electronics design.
About This Calculator
The Buck Converter Calculator helps electronics engineers, hobbyists, and students design and analyze DC-DC step-down switching regulators. A buck converter is a type of switched-mode power supply (SMPS) that efficiently converts a higher DC voltage to a lower DC voltage with minimal power loss, making it essential for battery-powered devices, computer power supplies, LED drivers, and solar systems.
The calculator computes the duty cycle D = Vout / Vin and the required inductance L = (Vin − Vout) × D / (fsw × Iripple), where fsw is the switching frequency and Iripple is the maximum inductor ripple current. It also provides the switch on-time (Ton) and off-time (Toff) for a complete timing picture.
Proper inductor selection is critical for buck converter performance — too low an inductance causes excessive ripple current and output voltage ripple, while too high an inductance increases size, cost, and slows transient response. The switching frequency selection balances efficiency, component size, and electromagnetic interference (EMI). Typical switching frequencies range from 100 kHz to 3 MHz depending on the application.
Regional Notes
Worldwide: Buck converter design follows the same electrical engineering principles globally. Input voltages vary: 12V DC is common in automotive (US/UK/IN), 5V for USB, 19-20V for laptop adapters, 48V for telecom and PoE applications. Output voltages are typically 1.2V-5V for ICs, 3.3V for logic, or 12V for peripherals. Always use the standard SI units (volts, kHz, amperes) for calculations.
Frequently Asked Questions
What is a buck converter and how does it work?
A buck converter is a DC-to-DC step-down converter that efficiently reduces a higher input voltage to a lower output voltage using a switching regulator. It works by controlling the energy transfer from input to output through a transistor switch, an inductor, a diode, and capacitors. The switch turns on and off at a high frequency (typically 100 kHz to 3 MHz), and the duty cycle determines the output voltage ratio.
How do you calculate the duty cycle of a buck converter?
The duty cycle D of a buck converter is calculated as D = Vout / Vin, where Vout is the desired output voltage and Vin is the input voltage. For example, with Vin = 12V and Vout = 5V, the duty cycle is 5/12 = 41.67%. Always ensure Vout is less than Vin as a buck converter only steps down voltage.
What is the formula for buck converter inductance?
The inductance L for a buck converter is calculated using L = (Vin - Vout) × D / (fsw × Iripple), where Vin is input voltage, Vout is output voltage, D is the duty cycle, fsw is the switching frequency in Hz, and Iripple is the maximum ripple current in amperes. The result is typically expressed in microhenries (µH).
How do I choose the switching frequency for a buck converter?
Switching frequency selection balances efficiency, component size, and performance. Use 100 kHz to 500 kHz for low-power applications, 1 MHz to 3 MHz for compact component designs, and above 3 MHz for lightweight high-efficiency designs. Higher frequencies allow smaller inductors but increase switching losses.
Can a buck converter step up voltage?
No, a buck converter is designed only as a step-down converter and cannot step up voltage. The output voltage will always be lower than the input voltage. To step up voltage, you need a boost converter, which uses a different circuit topology to produce a higher output voltage than the input.
What is the difference between continuous and discontinuous conduction mode in a buck converter?
In Continuous Conduction Mode (CCM), the inductor current never falls to zero during the switching cycle, providing lower ripple and better efficiency at higher loads. In Discontinuous Conduction Mode (DCM), the inductor current falls to zero before the next cycle, which typically occurs at light loads. CCM is preferred for most designs due to better regulation and efficiency.
Why is the duty cycle important in a buck converter?
The duty cycle directly determines the output voltage ratio and affects overall circuit efficiency. High duty cycles (above 80%) can lead to increased conduction and inductor losses, reducing efficiency. Moderate duty cycles around 30-70% typically offer the best balance between efficiency, thermal performance, and component stress.
What are typical applications of buck converters?
Buck converters are widely used in battery-powered devices (laptops, smartphones), solar panel MPPT systems, LED lighting drivers, computer power supplies (VRM for CPUs/GPUs), data center equipment, electric vehicles, USB power delivery, and any application requiring efficient voltage step-down from a higher DC voltage to a lower DC voltage.