2ST2121 Equivalent & Substitute Parts

Part Overview

The 2ST2121 is a PNP bipolar junction transistor manufactured by STMicroelectronics, rated for 250 V collector-emitter breakdown voltage and 17 A maximum collector current. This device is packaged in the TO-3 (TO-204AA) through-hole configuration and is designed for high-power switching and amplification applications with a maximum power dissipation of 250 W.

The 2ST2121 is classified as an obsolete product. Identifying equivalent substitute parts is necessary to maintain design continuity, ensure supply chain availability, and support ongoing production requirements for legacy systems utilizing this component.

Substiute Parts

2ST2121

STMicroelectronicsIn Stock: 11472ST2121 Datasheet

Current PartRFQ

MJ21193G

onsemiIn Stock: 1199MJ21193G Datasheet

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MJ21195G

onsemiIn Stock: 1817MJ21195G Datasheet

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Key Parameters

Substitute Part Grouping Explanation

Substitute parts for the 2ST2121 are identified based on strict electrical and mechanical parameter compatibility. The following criteria determine substitution eligibility:

Primary Matching Parameters:

• Transistor Type: PNP (required match)
• Voltage - Collector Emitter Breakdown (Max): 250 V (required match)
• Package / Case: TO-204AA or TO-3 (required match)
• Mounting Type: Through Hole (required match)
• Power - Max: 250 W (required match)
• RoHS Status: ROHS3 Compliant (required match)

Secondary Compatibility Parameters:

• Current - Collector (Ic) (Max): Substitute must support minimum 17 A or lower current rating depending on application requirements
• Operating Temperature Range: Substitute must support maximum junction temperature of 200°C or higher

The substitute parts MJ21193G and MJ21195G meet all primary matching parameters. Both devices are manufactured by onsemi, maintain active product status, and are available in the same TO-3 package configuration with identical voltage and power ratings.

Parameter Comparison

Engineering Selection Recommendations

Both MJ21193G and MJ21195G are suitable substitutes for the obsolete 2ST2121 based on compliance and product status criteria.

MJ21193G and MJ21195G Selection Basis:

• Both devices maintain active product status, ensuring long-term availability and supply chain continuity
• Both are ROHS3 compliant and REACH unaffected, meeting current environmental and regulatory requirements
• Both are packaged in TO-204 (TO-3) through-hole configuration, compatible with existing PCB layouts and mechanical assemblies
• Both maintain 250 V collector-emitter breakdown voltage and 250 W maximum power dissipation ratings
• Both support maximum junction temperature of 200°C, matching the thermal operating envelope of the original 2ST2121

Parameter Differences: The substitute parts operate at reduced maximum collector current (16 A versus 17 A) and lower transition frequency (4 MHz versus 25 MHz). These differences are acceptable for applications where the original 2ST2121 was not operating at maximum current or frequency specifications. Applications requiring the full 17 A current rating or 25 MHz transition frequency characteristics must evaluate circuit-level impact before substitution.

Frequently Asked Questions (FAQ)

Q: Can MJ21193G and MJ21195G be used interchangeably with the 2ST2121?

A: Both MJ21193G and MJ21195G share identical electrical ratings (250 V, 250 W, TO-3 package) and are functionally equivalent for applications not requiring the full 17 A current specification or 25 MHz transition frequency of the original device. Pin configuration and package dimensions are identical, enabling direct mechanical and electrical substitution in existing designs.

Q: What is the difference between MJ21193G and MJ21195G?

A: MJ21193G and MJ21195G are electrically identical devices with matching specifications. Both are manufactured by onsemi and rated for 250 V, 16 A, and 250 W. Selection between these two parts may be based on inventory availability or supplier preference, as no technical differentiation exists between them.

Q: Why does the 2ST2121 have a higher maximum collector current (17 A) than the substitute parts (16 A)?

A: The 2ST2121 is rated for 17 A maximum collector current, while MJ21193G and MJ21195G are rated for 16 A. This 1 A difference reflects different design specifications between manufacturers. For applications operating below 16 A, this difference is not significant. Applications requiring sustained operation above 16 A must evaluate whether the reduced current rating impacts circuit performance.

Q: Are the substitute parts compatible with existing PCB layouts designed for the 2ST2121?

A: Yes. Both MJ21193G and MJ21195G use the TO-204AA (TO-3) package with identical pin configuration and mechanical dimensions as the 2ST2121. No PCB modifications are required for substitution.

Q: What compliance certifications apply to the substitute parts?

A: Both MJ21193G and MJ21195G are ROHS3 compliant and REACH unaffected. These certifications match the compliance status of the original 2ST2121, ensuring regulatory compatibility in applications subject to environmental and hazardous substance restrictions.

Q: Why is the 2ST2121 classified as obsolete?

A: The 2ST2121 is no longer in active production by STMicroelectronics. The substitute parts MJ21193G and MJ21195G are actively manufactured by onsemi and provide equivalent functionality for new designs and legacy system support.

Q: What is the difference in transition frequency between the 2ST2121 (25 MHz) and the substitute parts (4 MHz)?

A: The 2ST2121 operates at 25 MHz transition frequency, while MJ21193G and MJ21195G operate at 4 MHz. This difference reflects different semiconductor design approaches. For switching applications operating below 4 MHz, this difference is not significant. High-frequency applications operating above 4 MHz must evaluate whether the reduced transition frequency impacts circuit performance and switching characteristics.