4554-121K Fixed Inductor Equivalent & Substitute Parts

Part Overview

The 4554-121K is a 120 µH unshielded through-hole inductor manufactured by API Delevan Inc., rated for 840 mA continuous current with a maximum DC resistance of 320 mOhm. This component is classified as Active product status and is suitable for general-purpose RF and power applications requiring fixed inductance values in radial, vertical cylinder package configuration.

Substitute parts become necessary when the original manufacturer part is unavailable, when supply chain constraints limit access to inventory, or when design requirements permit alternative manufacturers meeting identical electrical and mechanical specifications. The substitute identified maintains full parameter equivalence with the main part across all critical performance characteristics.

Key Parameters

Parameter	Value	Unit	Significance for Substitution
Inductance	120	µH	Primary electrical specification; must match exactly
Inductance Tolerance	±10%	%	Defines acceptable inductance range; must be equivalent or tighter
Current Rating	840	mA	Maximum continuous current; substitute must meet or exceed
DC Resistance (DCR)	320	mOhm Max	Power loss parameter; substitute must not exceed
Q Factor @ 796 kHz	20	—	Quality factor at test frequency; indicates core loss characteristics
Self-Resonant Frequency	3.4	MHz	Upper frequency limit; substitute must match
Mounting Type	Through Hole	—	PCB assembly method; must be identical
Package / Case	Radial, Vertical Cylinder	—	Physical form factor; must be identical for board compatibility
Size / Dimension	0.340" Dia (8.64 mm)	—	Footprint constraint; substitute diameter must be compatible
Height - Seated (Max)	0.433" (11.00 mm)	—	Board clearance requirement; substitute height must not exceed
Operating Temperature Range	-40°C ~ 85°C	—	Environmental specification; substitute range must encompass or exceed
Shielding	Unshielded	—	EMI characteristics; must match for circuit behavior consistency
Core Material	Ferrite	—	Determines frequency response and loss characteristics

Substitute Part Grouping Explanation

Substitution eligibility for the 4554-121K is determined by strict equivalence across the following critical parameters:

Electrical Parameters (Non-Negotiable):

Inductance value: 120 µH ±10%
Current rating: minimum 840 mA
DC resistance: maximum 320 mOhm
Q factor @ 796 kHz: 20 (indicating equivalent core loss)
Self-resonant frequency: 3.4 MHz
Shielding configuration: Unshielded

Mechanical Parameters (Non-Negotiable):

Mounting type: Through Hole
Package configuration: Radial, Vertical Cylinder
Diameter: compatible with 0.340" (8.64 mm) specification
Height: maximum 0.433" (11.00 mm)

Environmental Parameters:

Operating temperature range: must encompass -40°C to 85°C minimum
Core material: Ferrite

The substitute part RL622-121K-RC meets all specified criteria and is therefore classified as a direct equivalent.

Parameter Comparison

Parameter	4554-121K (API Delevan)	RL622-121K-RC (Bourns)	Match Status
Inductance	120 µH	120 µH	Equivalent
Inductance Tolerance	±10%	±10%	Equivalent
Current Rating	840 mA	840 mA	Equivalent
DC Resistance (DCR)	320 mOhm Max	320 mOhm Max	Equivalent
Q @ 796 kHz	20	20	Equivalent
Self-Resonant Frequency	3.4 MHz	3.4 MHz	Equivalent
Mounting Type	Through Hole	Through Hole	Equivalent
Package / Case	Radial, Vertical Cylinder	Radial, Vertical Cylinder	Equivalent
Diameter	0.340" (8.64 mm)	0.335" (8.50 mm)	Compatible
Height - Seated (Max)	0.433" (11.00 mm)	0.433" (11.00 mm)	Equivalent
Operating Temperature Range	-40°C ~ 85°C	-55°C ~ 105°C	Substitute Exceeds
Shielding	Unshielded	Unshielded	Equivalent
Core Material	Ferrite	Ferrite	Equivalent
Product Status	Active	Active	Equivalent

Engineering Selection Recommendations

Primary Part Selection (4554-121K): The 4554-121K remains the preferred selection when available. This part carries Active product status and maintains full inventory availability (795 pcs in stock). However, RoHS non-compliance status may restrict use in applications subject to RoHS3 regulatory requirements.

Substitute Part Selection (RL622-121K-RC): The RL622-121K-RC is a direct functional equivalent suitable for applications where the primary part is unavailable or where regulatory compliance is required. This substitute offers the following advantages:

Larger inventory availability (1642 pcs in stock)
Extended operating temperature range (-55°C to 105°C vs. -40°C to 85°C)
RoHS3 compliance status, meeting current environmental regulations
Identical electrical performance across all specified parameters
Mechanical compatibility with existing PCB designs (diameter 0.335" vs. 0.340" represents a 0.15 mm reduction, within typical PCB tolerance)

Selection Criteria:

If RoHS3 compliance is mandatory: select RL622-121K-RC
If extended temperature operation is required: select RL622-121K-RC
If supply availability is critical: select RL622-121K-RC (higher stock level)
If legacy system compatibility requires original manufacturer: select 4554-121K

Both parts are suitable for direct PCB substitution without circuit redesign.

Frequently Asked Questions (FAQ)

Q: Can RL622-121K-RC be used as a direct replacement for 4554-121K without circuit modification?

A: Yes. The RL622-121K-RC meets all electrical specifications (inductance, current rating, DC resistance, Q factor, and self-resonant frequency) and mechanical specifications (mounting type, package configuration, and height). The diameter difference (0.335" vs. 0.340") is within standard PCB tolerance and does not require design changes.

Q: What is the significance of the diameter difference between the two parts?

A: The 4554-121K has a diameter of 0.340" (8.64 mm), while the RL622-121K-RC has a diameter of 0.335" (8.50 mm). This 0.15 mm difference is negligible for through-hole PCB applications and falls within standard component tolerance ranges. Both parts fit standard radial inductor footprints without modification.

Q: Why does the RL622-121K-RC have a wider operating temperature range?

A: The RL622-121K-RC operates from -55°C to 105°C, compared to the 4554-121K range of -40°C to 85°C. This extended range is a design characteristic of the Bourns RL622 series and does not affect substitution compatibility. Applications requiring only -40°C to 85°C operation are fully supported by both parts.

Q: What is the difference between RoHS non-compliant and RoHS3 compliant status?

A: The 4554-121K carries RoHS non-compliant status, indicating it may contain restricted substances. The RL622-121K-RC is RoHS3 compliant, meeting current environmental regulations that restrict hazardous substances. For applications subject to RoHS3 requirements (EU markets, automotive, medical devices), the RL622-121K-RC is the required selection.

Q: Are there any performance differences between the ferrite cores used in each part?

A: Both parts use ferrite core material and deliver identical Q factor (20 @ 796 kHz) and self-resonant frequency (3.4 MHz) specifications. The core designs are functionally equivalent for circuit performance purposes.

Q: Can these parts be mixed in the same production batch?

A: Yes. Both parts meet identical electrical and mechanical specifications and can be used interchangeably in the same circuit design. However, for traceability and quality control purposes, many manufacturers prefer to maintain single-part-number consistency within a production batch.

Q: What is the significance of the "Drum Core, Wirewound" designation for the RL622-121K-RC?

A: This describes the physical construction method used by Bourns. The "Drum Core, Wirewound" construction achieves the same electrical performance as the API Delevan design while maintaining full parameter equivalence. This is a manufacturing detail that does not affect substitution compatibility.

Q: Is the RL622-121K-RC available in the same packaging options?

A: Both parts are supplied in Bulk packaging. Packaging format is identical, and both are suitable for automated PCB assembly processes.

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