STSA851 Equivalent & Substitute Parts

Part Overview

The STSA851 is an NPN bipolar junction transistor manufactured by STMicroelectronics, rated for 60 V collector-emitter breakdown voltage and 5 A maximum collector current. Packaged in TO-92-3 (TO-226AA) through-hole configuration, this device is designed for general-purpose switching and amplification applications requiring moderate voltage and current handling capability.

The STSA851 is classified as obsolete, necessitating identification of active equivalent and substitute components for new designs and ongoing production requirements. Substitute parts must maintain electrical compatibility within the specified parameter ranges while offering active product status and continued availability.

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	130	MHz
Vce Saturation (Max) @ Ib, Ic	450 mV @ 200 mA, 5 A	—
DC Current Gain (hFE) (Min) @ Ic, Vce	150 @ 2 A, 1 V	—
Mounting Type	Through Hole	—
Package / Case	TO-92-3	—
RoHS Status	ROHS3 Compliant	—

Substitute Part Grouping Explanation

Substitution of the STSA851 is determined by the following critical electrical parameters:

Voltage Rating: The collector-emitter breakdown voltage must equal or exceed 60 V to maintain circuit protection margins.

Current Rating: The maximum collector current must equal or exceed 5 A to support the intended load requirements.

Frequency Response: The transition frequency must support the switching or amplification speed requirements of the application.

Power Dissipation: The maximum power rating must accommodate the thermal load in the operating circuit.

Package Compatibility: Through-hole mounting in TO-92-compatible packages ensures mechanical and thermal compatibility with existing PCB designs.

Saturation Characteristics: Vce saturation voltage and associated bias conditions determine switching efficiency and logic-level compatibility.

DC Current Gain: Minimum hFE values establish base drive requirements and circuit biasing conditions.

The substitute parts identified below meet or exceed these critical parameters while offering active product status and improved availability.

Parameter Comparison

Parameter	STSA851 (Main)	ZTX851	ZTX1053A	ZTX1049A
Manufacturer	STMicroelectronics	Diodes Incorporated	Diodes Incorporated	Diodes Incorporated
Product Status	Obsolete	Active	Active	Active
Transistor Type	NPN	NPN	NPN	NPN
Voltage - Collector Emitter Breakdown (Max)	60 V	60 V	75 V	25 V
Current - Collector (Ic) (Max)	5 A	5 A	3 A	4 A
Power - Max	1.1 W	1.2 W	1 W	1 W
Frequency - Transition	130 MHz	130 MHz	140 MHz	180 MHz
Vce Saturation (Max) @ Ib, Ic	450 mV @ 200 mA, 5 A	250 mV @ 200 mA, 5 A	250 mV @ 100 mA, 3 A	220 mV @ 50 mA, 4 A
DC Current Gain (hFE) (Min) @ Ic, Vce	150 @ 2 A, 1 V	100 @ 2 A, 1 V	300 @ 1 A, 2 V	300 @ 1 A, 2 V
Current - Collector Cutoff (Max)	50 nA (ICBO)	50 nA (ICBO)	10 nA	10 nA
Operating Temperature	150°C (TJ)	−55°C ~ 200°C (TJ)	−55°C ~ 200°C (TJ)	−55°C ~ 200°C (TJ)
Mounting Type	Through Hole	Through Hole	Through Hole	Through Hole
Package / Case	TO-92-3	E-Line-3 (TO-92 compatible)	E-Line-3 (TO-92 compatible)	E-Line-3 (TO-92 compatible)
RoHS Status	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant
Moisture Sensitivity Level (MSL)	1 (Unlimited)	1 (Unlimited)	1 (Unlimited)	1 (Unlimited)
REACH Status	REACH Unaffected	REACH Unaffected	REACH Unaffected	REACH Unaffected

Engineering Selection Recommendations

Primary Substitute: ZTX851

The ZTX851 manufactured by Diodes Incorporated is the direct electrical equivalent of the STSA851. Both devices share identical voltage (60 V), current (5 A), and frequency (130 MHz) ratings. The ZTX851 offers superior saturation characteristics (250 mV versus 450 mV at 5 A), improved power rating (1.2 W versus 1.1 W), and extended operating temperature range (−55°C to 200°C versus 150°C maximum). The ZTX851 maintains active product status with high inventory availability (20,383 pieces in stock). Package compatibility is confirmed through E-Line-3 TO-92 compatible configuration. All regulatory compliance requirements are met: ROHS3 compliant, REACH unaffected, and MSL 1 rating.

Secondary Substitute: ZTX1053A

The ZTX1053A is suitable for applications where voltage margin is required. This device exceeds the STSA851 voltage rating at 75 V while maintaining the 130 MHz transition frequency. The maximum collector current is reduced to 3 A, limiting applicability to circuits requiring less than 3 A. The ZTX1053A provides improved saturation characteristics and extended temperature range. Active product status and adequate inventory (3,380 pieces) support production requirements.

Tertiary Substitute: ZTX1049A

The ZTX1049A is applicable only to circuits where the 5 A current requirement can be reduced to 4 A maximum. The voltage rating of 25 V is insufficient for the STSA851 specification and restricts this device to lower-voltage applications. The ZTX1049A offers the highest transition frequency (180 MHz) and superior saturation performance. Active product status and high inventory (5,400 pieces) provide availability assurance.

All substitute parts maintain through-hole mounting compatibility, ROHS3 compliance, and unlimited moisture sensitivity rating. Selection between primary and secondary substitutes depends on specific circuit voltage and current requirements.

Frequently Asked Questions (FAQ)

Q: Can the ZTX851 directly replace the STSA851 in existing designs?

A: Yes. The ZTX851 is electrically equivalent to the STSA851 across all critical parameters: 60 V voltage rating, 5 A current rating, and 130 MHz transition frequency. The E-Line-3 package is mechanically and thermally compatible with TO-92-3 through-hole PCB layouts. No circuit modifications are required.

Q: What is the primary advantage of using ZTX851 over STSA851?

A: The ZTX851 offers active product status, ensuring continued availability and supply chain stability. Additionally, the ZTX851 provides improved saturation voltage (250 mV versus 450 mV at 5 A), lower power dissipation, and extended operating temperature range (−55°C to 200°C versus 150°C).

Q: Is the ZTX1053A suitable for all STSA851 applications?

A: The ZTX1053A is suitable only for applications where the maximum collector current requirement does not exceed 3 A. The 75 V voltage rating provides additional margin above the 60 V STSA851 specification. Applications requiring the full 5 A current capability must use ZTX851 or equivalent 5 A devices.

Q: Why is the ZTX1049A listed as a substitute if it has only 25 V rating?

A: The ZTX1049A is listed as a substitute for applications operating at voltages below 25 V where the 4 A current capability is sufficient. This device is not suitable for circuits designed for the full 60 V rating of the STSA851. Selection of ZTX1049A requires circuit redesign verification.

Q: Are all substitute parts RoHS compliant?

A: Yes. The ZTX851, ZTX1053A, and ZTX1049A are all ROHS3 compliant with MSL 1 (unlimited) moisture sensitivity rating. All devices are REACH unaffected. Regulatory compliance is maintained across all substitute options.

Q: What is the package compatibility between TO-92-3 and E-Line-3?

A: The E-Line-3 package used by Diodes Incorporated substitute parts is mechanically and thermally compatible with TO-92-3 through-hole mounting. Both packages feature three leads in identical pin configurations suitable for standard TO-92 PCB footprints. No layout modifications are required.

Q: How do saturation voltage differences affect circuit performance?

A: The STSA851 exhibits 450 mV saturation voltage at 5 A, while ZTX851 exhibits 250 mV at the same conditions. Lower saturation voltage reduces power dissipation in switching applications and improves logic-level compatibility in digital circuits. The ZTX851 provides superior switching efficiency.

Q: Can multiple substitute parts be used interchangeably in the same design?

A: No. Each substitute part has distinct electrical characteristics. ZTX851 is the direct equivalent for full-specification applications. ZTX1053A and ZTX1049A have reduced current ratings and require circuit analysis to confirm suitability. Selection must be based on specific application voltage and current requirements.

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