DC resistance (DCR) loss is one of the two main loss components in any inductor—alongside core loss. At high DC current, DCR loss (I²R) often dominates total loss and is the primary driver of inductor heating. Getting DCR right is essential for efficiency and thermal design.
This guide explains how to calculate DCR loss, what factors affect it, and how to minimize it in your inductor design.
Shaanxi SiRui Technology Co., Ltd. engineers optimize DCR in every custom inductor design. Contact: sales@sirui-tech.com | Web: www.sirui-tech.com
1. DCR Formula
R = ρ × L / A, where ρ = 1.72×10⁻⁸ Ω·m (copper at 20°C), L = wire length, A = copper area.
Temperature effect: R(T) = R₂₀ × [1 + 0.00393 × (T – 20)]. At 100°C, DCR is ~31% higher than at 20°C. Always calculate at operating temperature.
2. DCR Loss Calculation
P_DCR = I_RMS² × DCR
Example: 10 A output, DCR = 5 mΩ at 100°C. P_DCR = 10² × 0.005 = 0.5 W. If core loss is 0.3 W, DCR is 62.5% of total loss.
3. Factors Affecting DCR
- Wire length: more turns = longer wire = higher DCR
- Wire area: thicker wire = lower DCR but more window space
- Fill factor: round wire ~40–50%, litz ~35–45%
- Temperature: rising DCR causes more loss, positive feedback
4. How to Minimize DCR Loss
- Thicker wire / more copper area
- Litz wire at high frequency (reduces AC resistance 2–5×)
- Optimize turns count (don’t over-design inductance)
- Larger core for more window area
- Multiple parallel wires (improves fill factor)
5. Typical DCR Values
| Inductance | Current | Typical DCR |
|---|---|---|
| 1 μH, high current | 50 A | 1–5 mΩ |
| 10 μH, medium | 10 A | 5–20 mΩ |
| 100 μH, low current | 1 A | 50–200 mΩ |
| 1 mH, signal level | 0.1 A | 1–10 Ω |
6. Measuring DCR
- Use 4-wire (Kelvin) milliohm meter for accurate low-resistance measurement
- Cross-check with AWG wire tables and winding length
- Measure at operating temperature or calculate from room temp
7. Sirui-Tech DCR Optimization
- Custom wire sizing for your current
- Parallel winding for low DCR
- Litz wire for high-frequency AC resistance reduction
- DCR spec at 20°C and estimated at operating temperature
- Prototype thermal verification
Conclusion
DCR loss (I²R) is often the dominant loss in high-current inductors. Calculate it at operating temperature, not room temperature. Balance DCR loss against core loss for optimum design. When DCR dominates, focus on more copper area, fewer turns, and larger core.
Need a low-DCR inductor design? Contact Sirui-Tech at sales@sirui-tech.com with your inductance and current requirements.