ZTX857STOB Equivalent & Substitute Parts

Part Overview

The ZTX857STOB is an NPN bipolar junction transistor manufactured by Diodes Incorporated, designed for general-purpose switching and amplification applications. This device features a 300 V collector-emitter breakdown voltage rating, 3 A maximum collector current, and 1.2 W power dissipation capability in a through-hole E-Line (TO-92 compatible) package. The ZTX857STOB is classified as obsolete, necessitating identification of active equivalent parts for new designs and ongoing production requirements. Substitute parts maintain identical electrical specifications and mechanical compatibility while offering active product status and improved availability.

Key Parameters

Parameter	Value	Unit
Transistor Type	NPN	—
Voltage - Collector Emitter Breakdown (Max)	300	V
Current - Collector (Ic) (Max)	3	A
Power - Max	1.2	W
Frequency - Transition	80	MHz
DC Current Gain (hFE) (Min) @ Ic, Vce	100 @ 500mA, 10V	—
Vce Saturation (Max) @ Ib, Ic	250mV @ 600mA, 3A	—
Current - Collector Cutoff (Max)	50nA (ICBO)	—
Operating Temperature Range	-55 to 200	°C (TJ)
Mounting Type	Through Hole	—
Package / Case	E-Line-3	—
RoHS Status	ROHS3 Compliant	—
Moisture Sensitivity Level (MSL)	1 (Unlimited)	—

Substitute Part Grouping Explanation

Substitution of the ZTX857STOB is determined by strict equivalence across all critical electrical and mechanical parameters. The substitute parts ZTX857 and ZTX857STZ are qualified as direct replacements based on the following criteria:

Electrical Parameter Equivalence:

Identical NPN transistor type
Identical maximum collector-emitter breakdown voltage (300 V)
Identical maximum collector current (3 A)
Identical maximum power dissipation (1.2 W)
Identical transition frequency (80 MHz)
Identical DC current gain specification (100 @ 500mA, 10V)
Identical saturation voltage specification (250mV @ 600mA, 3A)
Identical operating temperature range (-55°C to 200°C)

Mechanical and Packaging Equivalence:

Identical through-hole mounting type
Identical E-Line-3 package designation
Identical E-Line (TO-92 compatible) supplier device package
Identical RoHS3 compliance status
Identical MSL rating (1 - Unlimited)

Differentiation by Packaging Format: The substitute parts differ only in packaging configuration: ZTX857 is supplied in bulk packaging, while ZTX857STZ is supplied in cut tape (CT) format with formed leads. These packaging variations do not affect electrical performance or functional compatibility.

Parameter Comparison

Parameter	ZTX857STOB	ZTX857	ZTX857STZ
Manufacturer	Diodes Incorporated	Diodes Incorporated	Diodes Incorporated
Product Status	Obsolete	Active	Active
Transistor Type	NPN	NPN	NPN
Voltage - Collector Emitter Breakdown (Max)	300 V	300 V	300 V
Current - Collector (Ic) (Max)	3 A	3 A	3 A
Power - Max	1.2 W	1.2 W	1.2 W
Frequency - Transition	80 MHz	80 MHz	80 MHz
DC Current Gain (hFE) (Min) @ Ic, Vce	100 @ 500mA, 10V	100 @ 500mA, 10V	100 @ 500mA, 10V
Vce Saturation (Max) @ Ib, Ic	250mV @ 600mA, 3A	250mV @ 600mA, 3A	250mV @ 600mA, 3A
Operating Temperature Range	-55°C to 200°C (TJ)	-55°C to 200°C (TJ)	-55°C to 200°C (TJ)
Mounting Type	Through Hole	Through Hole	Through Hole
Package / Case	E-Line-3	E-Line-3	E-Line-3, Formed Leads
Supplier Device Package	E-Line (TO-92 compatible)	E-Line (TO-92 compatible)	E-Line (TO-92 compatible)
RoHS Status	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant
Moisture Sensitivity Level (MSL)	1 (Unlimited)	1 (Unlimited)	1 (Unlimited)
Packaging Format	Standard Tube	Bulk	Cut Tape (CT)
Inventory Status	996 Pcs New Original In Stock	6219 Pcs New Original In Stock	1086 Pcs New Original In Stock

Engineering Selection Recommendations

ZTX857 (Bulk Packaging): This part is the primary active equivalent to the ZTX857STOB. It maintains full electrical and mechanical compatibility with identical specifications across all critical parameters. The bulk packaging format is suitable for high-volume manufacturing environments and automated assembly processes. This part carries active product status, ensuring long-term availability and supply chain continuity.

ZTX857STZ (Cut Tape Packaging): This part provides an alternative active equivalent with identical electrical specifications. The cut tape format with formed leads is optimized for tape-and-reel feeding systems and automated pick-and-place assembly equipment. The formed leads configuration provides mechanical advantages in automated insertion processes. This part also carries active product status.

Selection Criteria: Choice between ZTX857 and ZTX857STZ depends solely on assembly process requirements and packaging format compatibility. Both parts deliver identical electrical performance and functional interchangeability. The ZTX857STOB, despite current inventory availability, should be replaced with either active equivalent for new designs due to its obsolete product status.

Frequently Asked Questions (FAQ)

Q: Can ZTX857 and ZTX857STZ be used interchangeably with ZTX857STOB?

A: Yes. Both ZTX857 and ZTX857STZ are direct electrical and mechanical equivalents to ZTX857STOB. All three parts share identical electrical specifications, operating parameters, and E-Line (TO-92 compatible) package dimensions. Substitution requires no circuit modifications or design changes.

Q: What is the difference between ZTX857 and ZTX857STZ?

A: The parts are electrically identical. The primary difference is packaging format: ZTX857 is supplied in bulk packaging, while ZTX857STZ is supplied in cut tape (CT) format with formed leads. The formed leads on ZTX857STZ are pre-shaped for automated tape-and-reel insertion equipment. Selection depends on assembly process compatibility.

Q: Why is ZTX857STOB classified as obsolete?

A: ZTX857STOB is listed as obsolete by the manufacturer. ZTX857 and ZTX857STZ are the active product line equivalents. For new designs and ongoing production, active equivalents should be specified to ensure long-term supply availability and manufacturer support.

Q: Are there any electrical performance differences between the three parts?

A: No. ZTX857STOB, ZTX857, and ZTX857STZ share identical electrical specifications including voltage ratings, current ratings, power dissipation, frequency response, gain characteristics, and saturation parameters. All three parts operate across the same temperature range (-55°C to 200°C).

Q: Can these parts be used in existing PCB designs without modification?

A: Yes. All three parts use the E-Line-3 package with E-Line (TO-92 compatible) pin configuration. PCB footprints, lead spacing, and mounting hole patterns are identical. Direct substitution on existing boards is possible without layout changes.

Q: What compliance certifications apply to all three parts?

A: All three parts are ROHS3 compliant, REACH unaffected, and carry MSL rating 1 (Unlimited moisture sensitivity level). Compliance status is identical across ZTX857STOB, ZTX857, and ZTX857STZ.

Q: Which part should be specified for new production designs?

A: Either ZTX857 or ZTX857STZ should be specified, as both carry active product status. ZTX857 is recommended for bulk assembly processes, while ZTX857STZ is recommended for automated tape-and-reel systems. ZTX857STOB should not be specified for new designs due to obsolete status.

Q: Is there a performance advantage to using formed leads (ZTX857STZ) over standard leads (ZTX857)?

A: Formed leads on ZTX857STZ provide mechanical advantages in automated insertion equipment by reducing lead bending and improving insertion reliability in tape-and-reel systems. Electrical performance is identical. Selection depends on assembly equipment compatibility, not performance requirements.

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