Series Inductor Calculator

L1:
L2:

Theory

1. RF Choke Design

RF chokes often use series inductors to achieve high impedance at specific frequencies while maintaining DC current capability. By connecting multiple smaller inductors in series, designers can:

  • Reduce parasitic capacitance compared to a single large inductor
  • Improve high-frequency performance
  • Better distribute heat generation
  • Achieve more precise impedance values

2. EMI Filter Design

EMI filters frequently employ series inductors to attenuate high-frequency noise. The advantages of using series inductors in EMI filters include:

  • Enhanced noise suppression across broader frequency ranges
  • Improved common-mode and differential-mode filtering
  • Reduced magnetic coupling between stages
  • More flexible filter response tuning

3. Power Supply Design

In power supply applications, series inductors are used to:

  • Create multi-stage input filters
  • Implement high-order output filters
  • Achieve specific voltage ripple requirements
  • Manage current slew rates

4. Series Connection Guide

How to add inductors in series:

Connection TypeFormulaCoupling EffectApplications
Simple SeriesLT = L1 + L2NoneBasic filtering
With Mutual CouplingLT = L1 + L2 + 2MAdditiveTransformers
Multiple InductorsLT = ΣLnComplexFilter chains

Coupled Inductors

Coupled inductors exhibit mutual inductance effects that can enhance or reduce the total inductance.

Coupling TypeTotal InductanceCoupling FactorApplications
Positive CouplingL1 + L2 + 2Mk > 0Transformers
Negative CouplingL1 + L2 - 2Mk < 0EMI Reduction
No CouplingL1 + L2k = 0Basic Filtering

Frequency Response

Understanding frequency response...

Frequency RangeImpedancePhaseConsiderations
Low FrequencyLowDC characteristics dominant
Mid FrequencyProportional to f90°Optimal Operating Range
High FrequencyLimited by Parasitic C<90°Self-resonance Effects

Testing Methods

Standard testing procedures...

Test TypeMethodParameters
DC Resistance4-wire measurementCurrent, Voltage
Inductance ValueLCR MeterFrequency, Test Signal
Coupling FactorMutual InductancePosition, Orientation

Connection Combinations

Different ways to combine series and parallel connections:

ConfigurationTotal InductanceAdvantagesApplications
Series-then-Parallel(L1+L2)||(L3+L4)Higher current handlingPower filters
Parallel-then-Series(L1||L2)+(L3||L4)Better heat distributionHigh current chokes

Design Considerations

Key factors to consider when designing series inductor circuits:

Design AspectSeries ConnectionSeries-Parallel
Current RatingLimited by weakest inductorCan be increased
Voltage StressDivided between inductorsBetter distribution
Heat ManagementCritical in compact designsMore flexible layout

Common Applications

Typical uses of series and series-parallel inductors:

ApplicationConfigurationBenefits
Power SuppliesSeries-ParallelBetter current handling
RF FiltersPure SeriesHigher impedance
EMI SuppressionCoupled SeriesCommon mode rejection

Implementation Tips

Practical considerations for implementing series inductor circuits:

AspectTechniqueImpact
PCB LayoutOrthogonal PlacementReduced coupling
ShieldingMagnetic ShieldLower interference
MountingSpaced MountingBetter thermal

Optimization Strategies

Methods to optimize series inductor designs:

StrategyMethodBenefit
Thermal ManagementDistributed LayoutHigher power capacity
Parasitic ControlSegmented WindingBetter HF response
Coupling ControlOriented PlacementPrecise mutual inductance

Theory

When inductors are connected in series, their total inductance is the sum of individual inductances. This principle stems from the physics of magnetic field energy storage in inductors.

LT = L1 + L2 + ... + Ln

Voltage Distribution

The voltage across each inductor is proportional to its inductance value. This relationship arises from the basic electromagnetic principle that induced voltage is proportional to the rate of change of magnetic flux.

Vn = V × (Ln / LT)

Design Considerations

Key factors to consider when designing series inductor circuits:

Design AspectSeries ConnectionSeries-Parallel
Current RatingLimited by weakest inductorCan be increased
Voltage StressDivided between inductorsBetter distribution
Heat ManagementCritical in compact designsMore flexible layout