KT503J2 Equivalent & Substitute Parts

Part Overview

The KT503J2 is an NTC thermistor with 50kΩ resistance at 25°C, manufactured by Littelfuse in a bead configuration with epoxy encapsulation. This component is classified as obsolete, making equivalent substitutes necessary for ongoing production and maintenance applications. The part operates at a maximum temperature of 120°C with 30mW power dissipation and features free-hanging mounting suitable for temperature sensing applications.

Substiute Parts

KT503J2

LittelfuseIn Stock: 846KT503J2 Datasheet

Current PartRFQ

B57861S0503F040

EPCOS - TDK ElectronicsIn Stock: 3321B57861S0503F040 Datasheet

MFR RecommendedRFQ

Key Parameters

Substitute Part Grouping Explanation

The B57861S0503F040 qualifies as a direct substitute based on the following critical parameters:

• Resistance Match: Both parts specify 50kΩ at 25°C, ensuring identical nominal impedance
• Thermal Characteristic Compatibility: The B Value at 25°C/100°C (3760K) falls within acceptable tolerance of the KT503J2's B0/50 specification (3892K), maintaining comparable temperature response curves
• Package Compatibility: Both utilize bead configuration with free-hanging mounting, allowing direct mechanical replacement
• Compliance Alignment: Both parts are ROHS3 compliant and share identical HTSUS and ECCN classifications
• Operating Temperature: The substitute's extended range (-55°C to 155°C) encompasses the KT503J2's maximum operating temperature of 120°C

Parameter Comparison

Engineering Selection Recommendations

The B57861S0503F040 is the qualified substitute for the obsolete KT503J2. Selection is based on:

• Product Availability: The KT503J2 is obsolete; the B57861S0503F040 maintains active production status with 3216 units in stock
• Regulatory Compliance: Both parts maintain ROHS3 compliance and identical trade classification codes, ensuring regulatory continuity
• Electrical Equivalence: Matching 50kΩ resistance and compatible B-value thermal characteristics preserve circuit performance within the specified operating range
• Mechanical Compatibility: Identical bead package configuration and comparable lead wire dimensions enable direct board-level substitution without redesign

Frequently Asked Questions (FAQ)

Q: Can the B57861S0503F040 be used as a direct replacement for the KT503J2?

A: Yes. Both parts share identical 50kΩ resistance at 25°C, compatible thermal response characteristics, and identical package configuration. The substitute's extended operating range and higher power rating provide additional design margin.

Q: What is the significance of the B-value difference (3892K vs. 3760K)?

A: The B-value defines the thermistor's temperature coefficient. The 3.4% difference between the KT503J2 (3892K) and B57861S0503F040 (3760K) results in comparable temperature response curves across the operating range. Both values are within acceptable tolerance for temperature sensing applications.

Q: Are there any lead wire length considerations?

A: Lead wire lengths differ by 0.02" (0.50mm): KT503J2 at 1.50" (38.00mm) versus B57861S0503F040 at 1.48" (37.50mm). This minimal difference is mechanically compatible for free-hanging mounting applications.

Q: Does the higher power rating of the substitute affect circuit design?

A: The B57861S0503F040 specifies 60mW maximum power dissipation compared to the KT503J2's 30mW. This provides additional thermal margin and does not require circuit modification for applications designed within the original 30mW specification.

Q: What compliance certifications apply to both parts?

A: Both the KT503J2 and B57861S0503F040 are ROHS3 compliant. The substitute is REACH Affected; the original part is REACH Unaffected. Both share EAR99 ECCN and 8533.40.8070 HTSUS classification.