Input Chokes

Input chokes introduce distributed line impedance that suppresses high-order current harmonics generated by diode or thyristor-based rectifiers. The added inductance at the input side lowers the steepness of current waveforms (di/dt), effectively reducing total harmonic distortion (THDi) and preventing voltage waveform distortion across the supply network. This reduction improves system compliance with harmonic limits defined by IEEE 519 and IEC 61000-3-12 without relying on active filtering techniques. 

Rated System Voltage

400 V / 415 V / 480 V / 690 V AC

Tuning Frequency

189 Hz / 210 Hz for 50 Hz systems

Inductance Tolerance

±5% (measured at rated current and 50 Hz)

Core Material

CRGO silicon steel / Amorphous metal

Insulation Class

Class H (180°C thermal endurance)

Product Description

Input chokes provide a first-order damping effect against steep voltage transients and line notches caused by switching operations, capacitor bank switching, or grid disturbances. The choke’s impedance introduces a delay in current rise time, thereby mitigating transient-induced overvoltages across rectifier diodes and input capacitors. This function ensures lower peak reverse voltage (PRV) across semiconductor junctions, significantly reducing the risk of device overstress or dielectric breakdown. 

Maximum Hot Spot Temperature

155°C continuous with 180°C short-duration withstand

Rated Harmonic Current

Up to 150% of fundamental current

Total Inductor Losses

≤ 3 W per reactive kVAR at rated harmonic profile

Dielectric Withstand Voltage

3 kV AC for 1 minute between windings and core

Magnetic Flux Density (Bmax)

≤ 1.6 Tesla at rated load, below saturation threshold

Short Circuit Thermal Withstand

1.8 x Irms for 1 second (IEC 60076-6 compliance)

Detuning Reactance (Uk%)

Typically 6%, 7%, or 14% depending on required detuning frequency

Winding Configuration

Copper/Aluminum, foil or round wire, thermally balanced with insulation barriers

Mounting Configuration

Base-mounted with vibration-damped brackets and slotted holes for alignment

Acoustic Noise Level

≤ 65 dB at 1 meter under rated harmonic loading

Technical Advantages

When capacitive loads such as DC link capacitors are energized, input chokes limit the initial inrush current by controlling the rate of current buildup. The inductive element acts as a series impedance, shaping the charging profile and preventing instantaneous current spikes that may otherwise trip protection devices or cause thermal stress on components. Proper choke sizing ensures compliance with upstream breaker and fuse characteristics during energization. 

Differential-mode noise resulting from high-frequency switching converters propagates back through the line and interferes with nearby systems. Input chokes present a high impedance to high-frequency components, attenuating conducted emissions in the 150 kHz to 30 MHz band. Their effectiveness in reducing differential noise contributes to EMC compliance per CISPR 11/22 Class A and B standards, especially in installations lacking active filtering or shielded cables. 

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Industry Applications

Variable Frequency Drives (VFDs)

Reduces input current harmonics, limits inrush, and protects front-end diodes from voltage transients during motor acceleration. 

UPS Systems

Enhances input power quality, reduces harmonic injection into the grid, and stabilizes line current during load transfer operations. 

AC-DC Converters

Minimizes ripple current, suppresses differential-mode EMI, and ensures smooth DC link capacitor charging during converter startup. 

Industrial Automation Panels

Improves electromagnetic compatibility, suppresses line noise, and stabilizes supply current under rapid load switching conditions. 

HVAC Control Systems

Limits input current distortion from compressor drives and ensures compliance with EN/IEC harmonics standards in building systems. 

CNC and Servo Drive Systems

Provides current filtering to prevent drive faults caused by back-fed harmonics and transient disturbances from regenerative loads.

Input Chokes

Saturation Avoidance Under Peak Current Conditions

High magnetizing current peaks during load transitions can saturate improperly sized inductors, leading to loss of inductive reactance and core heating. Input chokes designed with low-flux density and high-permeability core materials maintain linear inductance under full load and transient overload conditions. Air-gap optimization and core cross-section sizing prevent saturation, preserving functional integrity across the entire operating range. 

Continuous operation in high-temperature environments demands magnetic components with controlled thermal rise and insulation integrity. Input chokes constructed with Class H or N insulation systems, low-loss laminated or powder cores, and optimized winding configurations exhibit minimal temperature rise even under continuous rated current. Surface temperature stabilization ensures long-term performance without thermal runaway in sealed enclosures or compact panel systems. 

Input Chokes

Having Doubts? Our FAQ

Check all our Frequently Asked Question

How does Frigate design input chokes to handle high di/dt in modern high-frequency rectifiers?

Frigate designs input chokes with optimized core material and air gap to maintain stable inductance under rapid current rise conditions. This controls di/dt and limits current spikes that stress semiconductors. The winding geometry minimizes leakage inductance while ensuring thermal stability. These chokes are tested under switching transients to verify dynamic performance. 

What makes Frigate’s input chokes suitable for installations requiring low conducted emissions?

Frigate chokes are engineered to provide high differential-mode impedance across 150 kHz–30 MHz frequency range. This reduces EMI conducted back into the AC line from switching devices. Each choke is tested per CISPR 11/22 standards to verify emission compliance. The coil design and core selection target minimum high-frequency loss. 

 

How does Frigate prevent core saturation in input chokes during overload conditions?

Frigate uses high-permeability core materials with low flux density operation and precision air-gapped laminations. This allows the choke to maintain inductance during peak load surges. Thermal modeling ensures no hot spots under overload. Each unit is tested for saturation under maximum current to ensure consistent magnetic behavior. 

 

Can Frigate’s input chokes be used in systems with poor phase balance?

Frigate offers three-phase input chokes with matched inductance tolerance across all phases. This ensures current symmetry and suppresses imbalance-induced circulating currents. The core design supports operation under voltage distortion and unbalanced loading. Such chokes reduce neutral shift and improve upstream transformer efficiency. 

What thermal considerations are addressed in Frigate’s input choke construction?

Frigate selects Class H or N insulation and uses thermally stable cores with low eddy current losses. The winding fill factor is optimized to minimize hotspot development. Designs are verified using thermal simulations and validated through endurance tests. These chokes operate reliably in panels with ambient temperatures up to 120°C without derating. 

 

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LOCATIONS

Registered Office

10-A, First Floor, V.V Complex, Prakash Nagar, Thiruverumbur, Trichy-620013, Tamil Nadu, India.

Operations Office

9/1, Poonthottam Nagar, Ramanandha Nagar, Saravanampatti, Coimbatore-641035, Tamil Nadu, India. ㅤ

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Input Chokes

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Input Chokes

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