Inductor DCR Current-Sense Calculator
Design a lossless inductor DCR current sensing network for buck converters. Solves R and C for L·R/C·DCR = 1 matching.
How to Use
- Enter inductor L, DCR (DC resistance), and pick RC time constant = L/DCR.
- Tool computes R and C values with 1% matching.
Show Work
Formulas
History of Lossless Current Sensing
DCR current sensing emerged in the 2000s as CPU voltage regulator module (VRM) designs pushed above 100 A load current, where I-squared-R loss in a 5-milliohm sense resistor (~5 W) became unacceptable. Intersil (now Renesas) and Linear Technology pioneered the matching-RC-network technique in controller ICs like the ISL6559 and LTC3731. By 2010 every multiphase CPU VRM and server buck converter used DCR sensing; the technique also moved into motor drives and battery management.
About This Calculator
Enter inductor L, DCR (milliohms, from datasheet), sense cap C (typically 100 nF-1 µF), and load current for V_sense estimation. The tool solves R = L/(DCR·C) such that the RC time constant matches L/DCR — producing a capacitor voltage proportional to inductor current.
V_sense = I·DCR; pick the sense amp input range accordingly. For ±1% accuracy over temperature, add a thermistor voltage-divider for DCR compensation. Modern PWM controllers (ISL, TPS, MAX series) have built-in DCR sense networks with digital trim. Everything runs client-side.
About the Inductor DCR Current-Sense Calculator
Need a hand with electronics and circuit design? The Inductor DCR Current-Sense Calculator does the work for you — free, and right here in your browser. Design a lossless inductor DCR current sensing network for buck converters. Solves R and C for L·R/C·DCR = 1 matching.
How it works
Type your numbers into the boxes. The answer shows up right away — you do not have to press a button. If you change a number, the answer changes too. So you can try different numbers and watch what happens, or check an answer you worked out yourself. Just make sure each box has the right kind of number in it.
Want the deeper story? The Knowledge Base explains the ideas behind the tools in more detail.
Frequently Asked Questions
Why DCR sense?
Lossless current sensing — uses the inductor\'s own copper resistance (~1-10 mΩ) instead of a dedicated sense resistor. Saves ~1% efficiency at 20A load vs a 5 mΩ shunt.
Matching requirement?
RC time constant must match L/DCR for accurate current reporting. Mismatch creates dynamic errors during load transients. Use 1% resistors; capacitor tolerance less critical.
Temperature effect?
Copper DCR has +0.39%/°C TCR. For ±1% sense accuracy over temperature, compensate with NTC thermistor near the inductor. Precision regulators (TPS53679, ISL6596) have built-in DCR temp-comp.
How do I use the Inductor DCR Current-Sense Calculator?
Simply type your numbers and read the result, which refreshes the instant you change something. There is nothing to submit and nothing to wait for.
Is it free? Does it work without internet?
Yes to both. It is free with no sign-up, and once the page has loaded it keeps working even with no internet.
Where does my data go?
Nowhere — every calculation runs on your own device. Nothing you enter is uploaded, logged, or stored.
Common Use Cases
CPU VRM
Multiphase buck 12V→1V at 100A+: DCR sense saves multiple watts of sense-resistor loss.
DC Motor Control
High-current DC motor current sensing via stator coil DCR.
Battery Charger
Li-ion charger with inductor DCR sense for CC-mode regulation.
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