Buck inductor calculation: 12V to 3.3V / 5A
This example runs a built-in preset through the existing app calculation engine. Inputs, electrical results and one core-and-winding candidate are shown for review and reproduction.
What does this example verify?
This is a software calculation example with selected basic formulas and loss totals cross-checked. No prototype measurements are included, so it does not establish a percentage accuracy against hardware.
Inputs and constraints
| Item | Value or condition |
|---|---|
| Built-in preset | buck_12v_3v3_5a |
| Input voltage (minimum / nominal / maximum) | 10.8 / 12 / 13.2 V |
| Output | 3.3 V / 5 A |
| Topology / mode / frequency | Buck / CCM / 200 kHz |
| Ripple ratio ΔI / Iout | 25% |
| Ambient / rise limit / cooling | 25°C / 45°C / natural cooling |
| Inductor efficiency target (input) | 95% |
| Inductance tolerance / K_u preset | 20% / 0.4 |
| Winding settings | Round wire, thermal class F, heavy insulation build |
Electrical specification results
| Item | Value or condition |
|---|---|
| Output power | 16.5 W |
| Peak-to-peak ripple current | 1.25 A |
| Target inductance | 9.900 μH |
| Peak / RMS current | 5.625 / 5.013 A |
Core and winding candidate
| Item | Value or condition |
|---|---|
| Core / material / bobbin | E13/6/6.15 / N87 / BE13-1110CPSFR |
| Turns / wire | 10 / AWG 16 |
| Calculated gap | 0.2165 mm |
| Calculated inductance | 9.9000 μH |
| Peak flux density | 0.3257 T |
| Copper / core loss | 0.1124 / 0.0146 W |
| Estimated total loss | 0.1270 W |
| Estimated winding hotspot | 32.72 °C |
| Bobbin fill | 63% |
Scope of this run
The built-in inputs and constraints were retained, with round wire, thermal class F and heavy insulation build. This run checked only the first ten database E cores with Ae between 15 and 60 mm² and their default materials. The illustrated candidate has at least 10 turns, bobbin fill no greater than 65%, and a non-high proximity-risk category. It is not a global optimum or a purchase recommendation.
Independent numerical checks
At the maximum input of 13.2V: L = 3.3 × (1 − 3.3/13.2) / (200000 × 1.25) = 9.9μH. Peak current is 5 + 1.25/2 = 5.625A. RMS current is approximately 5.013A. These values match the engine output.
How close is this to a physical design?
This candidate retains a high-frequency warning and medium proximity-effect risk. The 32.72°C hotspot is a thermal-model estimate, not a thermocouple measurement. A near-zero model inductance error is not a manufacturing tolerance. Gap, material batch, winding layout and cooling still require prototype checks. The 95% input is an inductor efficiency target, not measured converter efficiency.
Reproduction and result record
Load the named preset in the corresponding app version, check the input and winding settings, and run the core-and-winding calculation. Database, version, settings and ranking changes can affect the candidates. The public record includes inputs, selected candidates, versions and source-file hashes; it is not an app-importable project file.
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