ZTX557STZ Equivalent & Substitute Parts

Part Overview

The ZTX557STZ is a PNP bipolar junction transistor manufactured by Diodes Incorporated, rated for 300 V collector-emitter breakdown voltage and 500 mA maximum collector current. This device is packaged in an E-Line (TO-92 compatible) through-hole configuration with a maximum power dissipation of 1 W and operates across a temperature range of -55°C to 200°C.

The ZTX557STZ is classified as an obsolete product. Identifying equivalent and substitute parts is necessary to maintain design continuity, ensure component availability, and support ongoing production and repair requirements for legacy systems utilizing this transistor.

Key Parameters

Parameter	Value	Unit
Transistor Type	PNP	—
Current - Collector (Ic) (Max)	500	mA
Voltage - Collector Emitter Breakdown (Max)	300	V
Power - Max	1	W
Frequency - Transition	75	MHz
Mounting Type	Through Hole	—
Package / Case	E-Line-3, TO-92 compatible	—
Operating Temperature Range	-55 to 200	°C
RoHS Status	ROHS3 Compliant	—

Substitute Part Grouping Explanation

Substitution of the ZTX557STZ is determined by equivalence in the following critical parameters:

Transistor Type: PNP configuration required for circuit polarity compatibility
Current Rating (Ic Max): 500 mA maximum collector current
Voltage Rating (Vce Breakdown): Minimum 300 V to maintain voltage margin
Mounting Type: Through-hole configuration for PCB compatibility
Package Compatibility: E-Line or TO-92-3 packages with formed leads

Substitute parts must satisfy all of these criteria simultaneously. Parts that meet or exceed the voltage and current ratings while maintaining the same package form factor and transistor polarity are considered functionally equivalent for direct replacement applications.

Parameter Comparison

Parameter	ZTX557STZ	ZTX757	2N6520TA	KSP92TA
Manufacturer	Diodes Incorporated	Diodes Incorporated	onsemi	onsemi
Transistor Type	PNP	PNP	PNP	PNP
Current - Collector (Ic) (Max)	500 mA	500 mA	500 mA	500 mA
Voltage - Collector Emitter Breakdown (Max)	300 V	300 V	350 V	300 V
Power - Max	1 W	1 W	625 mW	625 mW
Frequency - Transition	75 MHz	30 MHz	200 MHz	50 MHz
Mounting Type	Through Hole	Through Hole	Through Hole	Through Hole
Package / Case	E-Line-3	E-Line-3	TO-92-3	TO-92-3
Operating Temperature (Max)	200°C	200°C	150°C	150°C
Product Status	Obsolete	Active	Active	Active
RoHS Status	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant

Engineering Selection Recommendations

ZTX757 (Diodes Incorporated) is the primary manufacturer-recommended substitute. This part maintains identical voltage and current ratings (300 V, 500 mA) and shares the same E-Line-3 package form factor. Both devices are ROHS3 compliant and operate across the same temperature range (-55°C to 200°C). The ZTX757 is currently in active production status with high inventory availability (9430 pcs), ensuring long-term supply continuity. The transition frequency is lower (30 MHz versus 75 MHz), which is acceptable for applications not requiring the higher frequency performance of the original part.

KSP92TA (onsemi) is an alternative substitute meeting the 300 V voltage and 500 mA current specifications. This part uses a TO-92-3 package, which is mechanically compatible with E-Line-3 through-hole applications. The KSP92TA is ROHS3 compliant and maintains active production status with substantial inventory (85100 pcs). The maximum operating temperature is limited to 150°C compared to the original 200°C specification. The transition frequency of 50 MHz is lower than the original part but suitable for general-purpose switching applications.

2N6520TA (onsemi) provides the highest voltage rating (350 V) and fastest transition frequency (200 MHz) among the substitutes. This part is ROHS3 compliant and in active production. However, the maximum power dissipation is reduced to 625 mW, and the maximum operating temperature is limited to 150°C. The 2N6520TA is appropriate for applications requiring enhanced voltage margin or higher frequency operation within the reduced thermal envelope.

Selection between these substitutes depends on specific application requirements regarding frequency response, thermal operating conditions, and power dissipation limits.

Frequently Asked Questions (FAQ)

Q: Can the ZTX757 directly replace the ZTX557STZ in all applications?

A: The ZTX757 is electrically equivalent for voltage and current specifications and shares the same E-Line-3 package. Both devices are rated for 300 V and 500 mA with 1 W power dissipation. The primary difference is the transition frequency (30 MHz versus 75 MHz). Direct replacement is suitable for applications where the lower frequency performance is acceptable. Applications requiring the original 75 MHz transition frequency should evaluate the KSP92TA (50 MHz) or 2N6520TA (200 MHz) as alternatives.

Q: What is the difference between E-Line-3 and TO-92-3 packages?

A: Both E-Line-3 and TO-92-3 are through-hole packages with three formed leads in similar physical configurations. E-Line-3 is the Diodes Incorporated designation, while TO-92-3 is the onsemi designation. These packages are mechanically compatible for PCB mounting and lead spacing. Parts using either package designation can be substituted in applications designed for through-hole transistor mounting.

Q: Why is the maximum operating temperature different between substitutes?

A: The ZTX557STZ and ZTX757 are rated to 200°C junction temperature, while the KSP92TA and 2N6520TA are rated to 150°C. This reflects different device designs and thermal characteristics. Applications operating above 150°C junction temperature require the ZTX757 or original ZTX557STZ. For applications with maximum junction temperatures below 150°C, all substitutes are suitable.

Q: Can I use the 2N6520TA as a substitute if my application requires 1 W power dissipation?

A: The 2N6520TA is rated for 625 mW maximum power dissipation, which is lower than the original 1 W specification. If your application requires sustained 1 W dissipation, the 2N6520TA is not suitable. The ZTX757 maintains the full 1 W rating and is the appropriate choice for applications with this power requirement.

Q: Are all substitute parts RoHS compliant?

A: Yes. The ZTX557STZ, ZTX757, 2N6520TA, and KSP92TA are all ROHS3 compliant. All substitutes meet the same environmental and regulatory standards as the original part.

Q: What inventory status should I consider when selecting a substitute?

A: The ZTX757 has 9430 pcs in stock, and the KSP92TA has 85100 pcs in stock, both providing substantial availability. The 2N6520TA has 4580 pcs available. All three substitutes are in active production status, ensuring continued availability for future requirements. The original ZTX557STZ, though obsolete, has 718 pcs remaining in inventory.

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