What Is a Buck (Step-Down) Converter?
A buck converter (step-down converter) is a DC-DC converter that steps the input voltage down to a lower voltage with high efficiency.
How Does It Work?
A transistor switches on and off fast (PWM). While on, the inductor stores energy; while off, it releases that energy to the output through a diode/synchronous transistor. The larger the on-time (duty cycle), the higher the output voltage.
Duty Cycle and Output
In an ideal buck, Output ≈ Input × Duty Cycle. For example, a 25% duty cycle at 12 V input gives about 3 V output.
| Property | Value |
|---|---|
| Function | Steps the voltage down |
| Efficiency | 85-95% |
| Output | Lower than input |
When Instead of an LDO?
If the input-output difference is large and the current is high, a buck heats up far less than an LDO; where battery life and heat are critical, a buck is preferred.
Where Is It Used?
Common in producing 5V/3.3V from 12V, processor core voltages, vehicle electronics and LED supply.
Continuous and Discontinuous Mode
A buck runs in continuous conduction mode (CCM) if the inductor current never falls to zero, and in discontinuous mode (DCM) if it dips to zero at light load. CCM is more efficient at high load, while at light load DCM or pulse-skip mode reduces idle consumption.
Common Mistakes
- Inductor choice: a wrong inductance/current rating ruins efficiency and stability.
- Poor PCB layout: switching noise increases.
- Low input: if the input is very close to the output, clean step-down is difficult.
Frequently Asked Questions
Can a buck raise the voltage?+
What is a synchronous buck?+
Search parts related to "What Is a Buck (Step-Down) Converter?"
Find the right part by comparing price, stock and distributors.