Inductor

Inductor #

Stores energy in a magnetic field when current flows. Essential for filters, power supplies, and oscillators. Breadpad includes comprehensive parasitic modeling for realistic simulations.

Basic Properties #

  • Terminals: 2 (Start and End)
  • SPICE Designation: L
  • Default Value: 100 µH (0.0001 H)

Key Parameters #

Primary Parameter #

  • Inductance: Magnetic energy storage in Henries (H)
    • Common ranges: nanohenries (nH) to henries (H)
    • Automatically formatted with SI prefixes (e.g., 100µH, 10mH)

Parasitic Elements (Premium Features) #

  • Series Resistance (ESR): DC resistance of the wire

    • Typical: 0.01Ω - 10Ω depending on size
    • Critical for Q factor and power loss

  • Parallel Resistance: Core losses and leakage

    • Models hysteresis and eddy current losses
    • Typical: 10kΩ - 1MΩ

  • Parallel Capacitance: Turn-to-turn capacitance

    • Creates self-resonant frequency (SRF)
    • Typical: 1pF - 100pF

Temperature Coefficients #

  • TC1: Linear temperature coefficient (ppm/°C)

    • Ferrite cores: -1000 to +4000 ppm/°C
    • Air core: ~0 ppm/°C

  • TC2: Quadratic temperature coefficient (ppm/°C²)

    • Usually much smaller than TC1

Temperature-dependent inductance:

L(T) = L₀ × (1 + TC1×(T-T₀) + TC2×(T-T₀)²)

Tolerance (Premium Feature) #

  • Tolerance: Manufacturing variation
    • Standard: 10%, 20%
    • Precision: 1%, 2%, 5%
    • Used in Monte Carlo analysis

SPICE Model Architecture #

Breadpad creates a complete inductor model:

* Main inductor with parasitic elements
L1 LSTART1 2 100u
RS_L1 1 LSTART1 0.1      ; Series resistance
RP_L1 LSTART1 2 100k     ; Parallel resistance
CP_L1 LSTART1 2 10p      ; Parallel capacitance

With temperature coefficients:

L1 LSTART1 2 100u TC1=1000e-6 TC2=0

With tolerance (Monte Carlo):

L1 LSTART1 2 {100u*(1+gauss(0,0.10/3,6))}

Inductor Types and Applications #

Power Inductors #

  • Inductance: 1µH - 10mH
  • Current: 0.1A - 50A
  • ESR: 0.001Ω - 1Ω
  • Applications: DC-DC converters, VRMs

RF Inductors #

  • Inductance: 1nH - 100µH
  • Q Factor: 30-200
  • SRF: 100MHz - 10GHz
  • Applications: Filters, matching networks

Common Mode Chokes #

  • Inductance: 1mH - 100mH
  • Impedance: High for common mode
  • Applications: EMI suppression

Ferrite Beads #

  • Impedance: 10Ω - 1000Ω @ 100MHz
  • DC Resistance: < 1Ω
  • Applications: High-frequency noise suppression

Key Formulas #

Self-Resonant Frequency #

SRF = 1 / (2π√(L × Cp))

Quality Factor #

Q = 2πfL / ESR

Energy Storage #

E = ½ × L × I²

Impedance #

XL = 2πfL (inductive reactance)

Common Applications #

LC Filters #

  • Low-pass: Inductor in series
  • High-pass: Inductor in parallel
  • Cutoff: f_c = 1/(2π√(LC))

Switch-Mode Power Supplies #

  • Buck converter: Energy storage
  • Boost converter: Energy transfer
  • Flyback: Coupled inductors

RF Circuits #

  • Impedance matching
  • Tank circuits (with capacitor)
  • Bias chokes

EMI Filtering #

  • Differential mode: Series inductors
  • Common mode: Coupled inductors
  • Ferrite beads for HF noise

Design Considerations #

Saturation Current #

  • Core saturates at high current
  • Inductance drops dramatically
  • Check I_sat in datasheets

DCR (DC Resistance) #

  • Causes I²R power loss
  • Affects efficiency
  • Lower DCR = larger, more expensive

Core Materials #

  • Ferrite: High frequency, moderate current
  • Powdered Iron: High current, lower frequency
  • Air Core: No saturation, lower inductance

Simulation Tips #

  1. Parasitic Modeling: Include ESR for accurate power loss
  2. Self-Resonance: Add Cp for frequencies > SRF/10
  3. Saturation: Use PWL inductance for nonlinear behavior
  4. Temperature: Use TC1/TC2 for thermal analysis
  5. Initial Current: Use IC=current for startup analysis
  6. Coupled Inductors: Use K statement for transformers

See Also #