ZTX851STZ Equivalent & Substitute Parts

Part Overview

The ZTX851STZ is an NPN bipolar junction transistor manufactured by Diodes Incorporated, designed for general-purpose switching and amplification applications. This device operates at a maximum collector current of 5 A with a collector-emitter breakdown voltage of 60 V, making it suitable for moderate-power applications requiring through-hole mounting. The ZTX851STZ is currently in active product status with 1130 units in stock. Substitute parts become necessary when the primary device reaches end-of-life status, inventory constraints occur, or design flexibility is required across manufacturing sources while maintaining electrical and mechanical compatibility.

Substiute Parts

ZTX851STZ

Diodes IncorporatedIn Stock: 1196ZTX851STZ Datasheet

Current PartRFQ

STSA1805-AP

STMicroelectronicsIn Stock: 20676STSA1805-AP Datasheet

MFR RecommendedRFQ

Key Parameters

Substitute Part Grouping Explanation

Substitution of the ZTX851STZ is determined by strict equivalence across the following critical parameters:

Mandatory Matching Parameters:

• Transistor Type: NPN configuration
• Current - Collector (Ic) Max: 5 A minimum
• Voltage - Collector Emitter Breakdown (Max): 60 V minimum
• Mounting Type: Through Hole
• Package Compatibility: TO-92 or TO-92-compatible form factor
• RoHS Compliance: ROHS3 Compliant

Acceptable Variation Parameters:

• Power dissipation may be equal to or lower than the main part specification
• Transition frequency may exceed the main part specification
• DC Current Gain (hFE) may differ provided minimum specifications are met
• Operating temperature range may be narrower than the main part
• Vce Saturation characteristics may vary within acceptable switching performance

The STSA1805-AP from STMicroelectronics meets all mandatory matching parameters and qualifies as a direct substitute for the ZTX851STZ in applications where the specified electrical ratings are required.

Parameter Comparison

Engineering Selection Recommendations

Primary Part Selection (ZTX851STZ): The ZTX851STZ is the preferred selection for new designs and applications requiring active product status with ongoing manufacturer support. This device is currently in active production with 1130 units available in inventory. The part carries full ROHS3 compliance and REACH unaffected status, meeting current regulatory requirements.

Substitute Part Selection (STSA1805-AP): The STSA1805-AP qualifies as an electrical and mechanical substitute for the ZTX851STZ based on equivalent collector current rating (5 A), collector-emitter breakdown voltage (60 V), through-hole mounting configuration, and TO-92-compatible package form factor. Both devices are ROHS3 compliant and carry identical ECCN and HTSUS classifications.

The STSA1805-AP carries a Last Time Buy product status, indicating that STMicroelectronics has announced end-of-production for this device. This status should be considered when selecting this part for new designs or long-term production commitments. The substitute part exhibits higher transition frequency (150 MHz versus 130 MHz) and lower maximum power dissipation (1.1 W versus 1.2 W), which may affect suitability in power-limited or frequency-sensitive applications.

Compliance Considerations: Both parts maintain ROHS3 compliance and REACH unaffected status. Moisture sensitivity level is identical (MSL 1 - Unlimited) for both devices, eliminating special handling requirements during storage and assembly.

Frequently Asked Questions (FAQ)

Q: Can the STSA1805-AP be used as a direct replacement for the ZTX851STZ in existing designs?

A: The STSA1805-AP meets the mandatory electrical and mechanical parameters for substitution: 5 A collector current, 60 V breakdown voltage, NPN configuration, and TO-92-compatible through-hole package. However, the substitute part exhibits higher Vce saturation (600mV versus 250mV at rated current), which may affect switching speed and power dissipation in saturation-mode applications. Circuit-level validation is required to confirm compatibility with specific application requirements.

Q: What are the key differences between these two parts?

A: The primary differences are: (1) Vce saturation is higher in the STSA1805-AP (600mV versus 250mV), (2) transition frequency is higher in the STSA1805-AP (150MHz versus 130MHz), (3) maximum power dissipation is lower in the STSA1805-AP (1.1W versus 1.2W), and (4) product status differs (Active versus Last Time Buy). The STSA1805-AP also exhibits lower collector cutoff current (100nA versus 1µA) and higher DC current gain (200 versus 100).

Q: Are the package dimensions identical between ZTX851STZ and STSA1805-AP?

A: Both devices use TO-92-compatible through-hole packages with formed leads. The ZTX851STZ uses E-Line-3 packaging while the STSA1805-AP uses TO-226-3/TO-92-3 (TO-92AP) packaging. These package types are mechanically compatible for through-hole PCB mounting and pin-to-pin layout purposes.

Q: What is the significance of the Last Time Buy status for the STSA1805-AP?

A: Last Time Buy status indicates that STMicroelectronics has announced the end of production for the STSA1805-AP. This part should not be selected for new designs requiring long-term production support or extended component availability. The ZTX851STZ, with Active product status, is the appropriate choice for designs requiring ongoing manufacturer support and guaranteed future availability.

Q: Are there any thermal operating range limitations when substituting the STSA1805-AP?

A: The STSA1805-AP specifies a maximum operating temperature of 150°C, compared to 200°C for the ZTX851STZ. Applications requiring operation above 150°C junction temperature cannot use the STSA1805-AP as a substitute. The ZTX851STZ supports the full -55°C to 200°C operating range.

Q: How do the saturation characteristics affect circuit performance?

A: The STSA1805-AP exhibits 600mV Vce saturation at rated current (5A, 200mA base current) compared to 250mV for the ZTX851STZ. In switching applications, this higher saturation voltage results in increased power dissipation during the on-state and may require circuit redesign to maintain thermal performance specifications. In linear amplification applications, this difference may affect output impedance and gain characteristics.

Q: Are both parts suitable for high-frequency switching applications?

A: The STSA1805-AP offers higher transition frequency (150MHz) compared to the ZTX851STZ (130MHz), making it potentially more suitable for higher-frequency switching applications. However, the higher Vce saturation of the STSA1805-AP may limit switching speed in saturation-mode circuits. Application-specific circuit analysis is required to determine which device provides optimal performance.