Why is Vout not always exactly D Vin?

D Vin is the ideal continuous-conduction average. In discontinuous conduction the inductor fully demagnetizes each cycle, so the load resistance and inductance change the conversion ratio.

What does the CCM/DCM boundary mean?

At the boundary the inductor valley current just reaches zero. Higher load current or larger inductance keeps current continuous; lighter load or smaller inductance produces an idle part of the switching period.

Buck Converter Ripple

Step-down DC-DC converter: duty cycle, inductor ripple, CCM/DCM boundary, capacitor ESR ripple, and switching waveform sketch.

The model is an ideal asynchronous buck converter with a simple DCM estimate. It omits MOSFET switching loss, diode reverse recovery, core saturation, layout parasitics, control-loop stability, and transient load response.

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About this model

A buck converter steps a DC input down by switching an inductor between the source and the freewheel path. In continuous-conduction mode the ideal average output is Vout ≈ D Vin, while the inductor current ripple is set by the volt-second balance: ΔIL = (Vin - Vout)D/(L fs). At light load or small inductance the current can hit zero and the converter enters discontinuous-conduction mode, where Vout depends on load as well as duty cycle. This simulator estimates CCM/DCM mode, boundary inductance, output capacitor ripple, ESR ripple, and draws the power stage plus one switching-period current waveform.

Who it's for: Power electronics, embedded hardware, robotics, electrical engineering labs, and anyone sizing a DC-DC output filter.

Key terms

Buck converter
Duty cycle
Inductor ripple
CCM
DCM
Output capacitor ripple

How it works

Buck converter calculator for duty cycle, output voltage, inductor current ripple, CCM/DCM boundary, capacitor ripple, and switching waveforms.

Key equations

CCM: Vout ≈ D Vin, ΔIL = (Vin − Vout)D/(L fs)

Boundary: Lcrit = (1 − D)R/(2fs), ΔVout ≈ ΔIL/(8fsC) + ΔIL·ESR

Frequently asked questions

Why is Vout not always exactly D Vin?: D Vin is the ideal continuous-conduction average. In discontinuous conduction the inductor fully demagnetizes each cycle, so the load resistance and inductance change the conversion ratio.
What does the CCM/DCM boundary mean?: At the boundary the inductor valley current just reaches zero. Higher load current or larger inductance keeps current continuous; lighter load or smaller inductance produces an idle part of the switching period.

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Buck Converter Ripple

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About this model

How it works

Key equations

Frequently asked questions

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Live graphs

About this model

How it works

Key equations

Frequently asked questions