903 - Inductor Saturation¶

Non-linear inductance modeling and saturation effects.

Overview¶

Inductor saturation occurs when the core's magnetic flux density approaches Bsat, causing: - Dramatic inductance drop - Current spike - Potential device damage - Control instability

Saturation Physics¶

B-H Relationship¶

At saturation: $\(\mu_r \rightarrow 1\)$ (core behaves like air)

Inductance vs Current¶

As i increases → H increases → μr decreases → L decreases

Saturation Models¶

Piecewise Linear¶

Simple three-region model:

L(i)
  │
Lnom├────────┐
  │         │
  │         └────────
Lsat├──────────────────
  │
  └─────────────────── i
       Isat

Smooth Saturation¶

More realistic model: $\(L(i) = \frac{L_0}{1 + (i/I_{sat})^n}\)$

Where n controls transition sharpness (typically 2-6)

Jiles-Atherton¶

Physics-based model including: - Anhysteretic magnetization - Domain wall motion - Energy loss (hysteresis)

Impact on Converter Operation¶

DC-DC Converter¶

Normal operation (CCM): - Triangle current waveform - Predictable ripple

Saturated operation: - Current spike during on-time - Potential switch damage - EMI increase

Current at Saturation¶

With air gap: $\(I_{sat} = \frac{B_{sat} \cdot l_g}{\mu_0 \cdot N}\)$

Design for Saturation Avoidance¶

Method 1: Air Gap¶

Add gap to reduce effective permeability: $\(\mu_{eff} = \frac{\mu_r}{1 + \mu_r \cdot l_g/l_e}\)$

Benefits: - Stores energy in gap - Soft saturation characteristic - Stable inductance vs temperature

Method 2: Larger Core¶

Increase Ae to reduce B for given flux: $\(B = \frac{L \cdot I_{peak}}{N \cdot A_e}\)$

Method 3: Distributed Gap Materials¶

Powder cores (Kool Mμ, MPP, etc.): - Inherent distributed gap - Soft saturation - Higher core losses

Saturation Effects Analysis¶

Buck Converter Example¶

Transient Response¶

During load step: 1. Current increases toward new operating point 2. If current exceeds Isat, L drops suddenly 3. di/dt increases dramatically 4. Current overshoots

GeckoCIRCUITS Saturation Modeling¶

Using Non-linear Inductor¶

1. Select saturating inductor component
2. Enter parameters:
3. Nominal inductance L0
4. Saturation current Isat
5. Saturated inductance Lsat
6. Or use flux-linkage characteristic

Using Magnetic Domain¶

1. Create permeance with saturation
2. Enter B-H curve data points
3. Connect winding to electrical circuit
4. Observe flux and inductance vs current

Simulation Exercises¶

1. Compare linear vs saturating inductor
2. Observe current waveform at saturation boundary
3. Design air gap to prevent saturation
4. Analyze startup transient with saturation

Design Guidelines¶

Maximum Flux Density¶

Safety Margin¶

Design for: $\(I_{peak} \leq 0.8 \cdot I_{sat}\)$

Account for: - Load transients - Temperature variation (Bsat decreases with temp) - Component tolerance

Related Resources¶

• 901 - Magnetic Domain
• 902 - Transformer Design