STSA1805 Equivalent & Substitute Parts

Part Overview

The STSA1805 is an NPN bipolar junction transistor manufactured by STMicroelectronics, rated for 60 V collector-emitter breakdown voltage and 5 A maximum collector current. This device is packaged in TO-92-3 (TO-226AA) through-hole configuration and is designed for general-purpose switching and amplification applications requiring moderate current handling at moderate voltage levels.

The STSA1805 is classified as obsolete. Equivalent and substitute parts are necessary to maintain design continuity and ensure component availability for new production, repair, and maintenance applications where this transistor specification is required.

Key Parameters

Parameter	Value	Unit
Transistor Type	NPN	—
Voltage - Collector Emitter Breakdown (Max)	60	V
Current - Collector (Ic) (Max)	5	A
Power - Max	1.1	W
Frequency - Transition	150	MHz
Mounting Type	Through Hole	—
Package / Case	TO-92-3 (TO-226AA)	—
Operating Temperature (Max)	150	°C
RoHS Status	ROHS3 Compliant	—

Substitute Part Grouping Explanation

Substitution of the STSA1805 is determined by the following critical parameters:

Primary Substitution Criteria:

Transistor type must be NPN
Voltage - Collector Emitter Breakdown must be 60 V or greater
Current - Collector (Ic) maximum must be 5 A or greater
Mounting type must be through-hole compatible
Package must be TO-92-3 or mechanically compatible equivalent (E-Line TO-92 compatible)
RoHS3 compliance required

Secondary Compatibility Factors:

Power dissipation capability of 1.1 W or greater
Transition frequency of 130 MHz or greater
Operating temperature range supporting 150°C or higher

Substitute parts are grouped into two categories based on current rating alignment:

Category A - Full Current Rating Match (5 A): Parts with 5 A maximum collector current provide direct functional equivalence for applications requiring the full 5 A specification.

Category B - Reduced Current Rating (4.5 A or 1 A): Parts with lower maximum collector current ratings are suitable for applications where the circuit design operates below the substitute part's current limit, provided all other electrical parameters are met.

Parameter Comparison

Parameter	STSA1805 (Main)	KSD1616AGBU	ZTX851	ZX5T851A	ZXTN2010A
Manufacturer	STMicroelectronics	onsemi	Diodes Incorporated	Diodes Incorporated	Diodes Incorporated
Transistor Type	NPN	NPN	NPN	NPN	NPN
Voltage - Collector Emitter Breakdown (Max)	60 V	60 V	60 V	60 V	60 V
Current - Collector (Ic) (Max)	5 A	1 A	5 A	4.5 A	4.5 A
Power - Max	1.1 W	750 mW	1.2 W	1 W	1 W
Frequency - Transition	150 MHz	160 MHz	130 MHz	130 MHz	130 MHz
Mounting Type	Through Hole	Through Hole	Through Hole	Through Hole	Through Hole
Package / Case	TO-92-3 (TO-226AA)	TO-92-3 (TO-226AA)	E-Line-3 (TO-92 compatible)	E-Line-3 (TO-92 compatible)	E-Line-3 (TO-92 compatible)
Operating Temperature (Max)	150°C	150°C	200°C	150°C	150°C
Product Status	Obsolete	Active	Active	Active	Active
RoHS Status	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant

Engineering Selection Recommendations

Primary Substitute - ZTX851 (Diodes Incorporated)

The ZTX851 is the preferred substitute for the STSA1805. This part maintains full electrical equivalence with 5 A maximum collector current and 60 V breakdown voltage. The ZTX851 offers superior specifications including 1.2 W power dissipation (exceeding the 1.1 W requirement), E-Line packaging that is mechanically compatible with TO-92-3 footprints, and an extended operating temperature range to 200°C. The device is in active production status with ROHS3 compliance and high inventory availability (20,383 units).

Secondary Substitute - ZXTN2010A (Diodes Incorporated)

The ZXTN2010A provides functional substitution for applications where collector current requirements do not exceed 4.5 A. This part shares identical electrical characteristics with the ZTX851 (130 MHz transition frequency, 1 W power dissipation, 60 V breakdown voltage) and offers the highest inventory availability (16,400 units). The ZXTN2010A is suitable for designs with current margins below the 5 A specification.

Secondary Substitute - ZX5T851A (Diodes Incorporated)

The ZX5T851A is functionally equivalent to ZXTN2010A with 4.5 A maximum collector current. This part is suitable for applications with current requirements below 4.5 A and offers the same electrical performance characteristics. Inventory availability is lower (1,280 units) compared to other active substitutes.

Limited Substitute - KSD1616AGBU (onsemi)

The KSD1616AGBU is suitable only for applications where collector current requirements do not exceed 1 A. This part has reduced current rating (1 A maximum) and reduced power dissipation (750 mW) compared to the STSA1805. The KSD1616AGBU maintains 60 V breakdown voltage and TO-92-3 packaging compatibility. This substitute is appropriate for low-current switching applications only and is not suitable for designs requiring the full 5 A capability of the original part.

All substitute parts are ROHS3 compliant and REACH unaffected, meeting regulatory requirements equivalent to the STSA1805.

Frequently Asked Questions (FAQ)

Q: Can the KSD1616AGBU directly replace the STSA1805 in all applications?

A: No. The KSD1616AGBU has a maximum collector current rating of 1 A, while the STSA1805 is rated for 5 A. The KSD1616AGBU is suitable only for applications where circuit design ensures collector current does not exceed 1 A. For applications requiring the full 5 A capability, use ZTX851 or ZX5T851A instead.

Q: Are the E-Line packages (ZTX851, ZX5T851A, ZXTN2010A) mechanically compatible with TO-92-3 PCB footprints?

A: Yes. E-Line-3 packages are mechanically compatible with TO-92-3 (TO-226AA) footprints. The three-lead configuration and pin spacing are equivalent, allowing direct board-level substitution without PCB redesign.

Q: What is the difference between ZTX851, ZX5T851A, and ZXTN2010A?

A: All three parts share identical electrical specifications (60 V breakdown, 130 MHz transition frequency, 1 W power dissipation, -55°C to 150°C operating range). The primary difference is inventory availability: ZTX851 has 20,383 units, ZXTN2010A has 16,400 units, and ZX5T851A has 1,280 units. All three are suitable for applications with collector current requirements up to 4.5 A.

Q: Does the ZTX851 extended operating temperature range (to 200°C) provide additional design margin?

A: Yes. The ZTX851 supports junction temperatures up to 200°C, compared to 150°C for the STSA1805 and other substitutes. This extended range provides additional thermal margin for applications operating in high-temperature environments.

Q: Are all substitute parts RoHS3 compliant?

A: Yes. All substitute parts listed (KSD1616AGBU, ZTX851, ZX5T851A, ZXTN2010A) are ROHS3 compliant and REACH unaffected, meeting the same regulatory requirements as the STSA1805.

Q: Which substitute has the highest transition frequency?

A: The KSD1616AGBU has the highest transition frequency at 160 MHz, compared to 150 MHz for the STSA1805 and 130 MHz for the Diodes Incorporated substitutes. However, frequency selection should be based on circuit requirements rather than maximum specification alone.

Q: Can I use ZX5T851A or ZXTN2010A in a design that requires 5 A collector current?

A: No. Both ZX5T851A and ZXTN2010A have maximum collector current ratings of 4.5 A. For applications requiring 5 A operation, use ZTX851, which maintains the full 5 A rating of the original STSA1805.

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