Buck Inductor Ripple⚠ unverified
Electrical / Power Electronics · Compute the peak-to-peak inductor current ripple in a buck converter
Parameters
| Input | Symbol | Unit | Default | Description |
|---|---|---|---|---|
| Vin | Vin | V | 1.0 | Input voltage |
| Vout | Vout | V | 1.0 | Output voltage |
| L | L | H | 1.0 | Inductance |
| f | f | Hz | 1.0 | Switching frequency |
| D | D | — | 1.0 | Duty cycle (dimensionless). Default is None, in which case it is computed from ``buck_converter_duty(Vin, Vout)`` |
| Output | Symbol | Unit | Description |
|---|---|---|---|
| result | ΔI | A | Peak-to-peak inductor current ripple, in amperes (A) |
The science & history
Understanding the Parameters
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$V_{in}$, $V_{out}$ — the on-state inductor voltage is $V_{in}-V_{out}$. Larger step-down (high $V_{in}$, low $V_{out}$) increases the ramp rate and thus ripple for fixed $L$ and $f$.
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$L$ — larger inductance slows $di/dt$ and reduces $\Delta I$ (at the cost of size, cost, and slower transient response).
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$f$ — higher switching frequency shortens the on interval, cutting ripple proportionally (until core/switching losses dominate).
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$D$ — on-time fraction. For an ideal buck in CCM, $D = V_{out}/V_{in}$ (see Buck Converter Duty Cycle); the registry treats $D$ as an independent input so you can use a measured or commanded duty.
Derivation (Approaching a Proof)
While the high-side switch is on for time $t_{on} = D/f$, the inductor sees approximately constant voltage $V_L = V_{in} - V_{out}$ (ideal switch and diode/sync-FET drops neglected). From $v = L\,di/dt$,
$$\Delta I = \frac{V_L}{L}\,t_{on} = \frac{(V_{in} - V_{out})}{L}\cdot\frac{D}{f} = \frac{(V_{in} - V_{out})\,D}{L\,f}.$$
During the off interval the current ramps down by the same $\Delta I$ (steady state: volt-second balance). The triangular ripple sits on the DC load current $I_{out}$; continuous conduction requires $I_{out} > \Delta I/2$.
Check with ideal $D$: substituting $D = V_{out}/V_{in}$ gives the common form $\Delta I = V_{out}(1-D)/(L f) = V_{out}(V_{in}-V_{out})/(V_{in} L f)$.
History
Inductor ripple sizing has been standard buck-converter design practice since early switch-mode regulators. Modern point-of-load modules still quote $\Delta I$ targets (often 20–40% of $I_{out}$) as a rule of thumb balancing size, efficiency, and transient response.
Related Concepts: Buck Converter Duty Cycle, Output Voltage Ripple, Inductor Stored Energy, Conduction Loss
Notes: Registry calculator buck-inductor-ripple (unverified). Ideal CCM; ignores DCR, switch
drops, and discontinuous mode. Units: $L$ in H, $f$ in Hz → $\Delta I$ in A.