STPSA42 Equivalent & Substitute Parts

Part Overview

The STPSA42 is an NPN bipolar junction transistor (BJT) manufactured by STMicroelectronics, rated for 300 V collector-emitter breakdown voltage and 500 mA maximum collector current. The device is packaged in a TO-92-3 through-hole configuration with a maximum power dissipation of 625 mW and transition frequency of 50 MHz. The STPSA42 is classified as obsolete, necessitating identification of equivalent and substitute components for ongoing design support and production requirements. Substitute parts must maintain electrical compatibility within the specified parameter ranges while accommodating available product status and packaging options.

Key Parameters

Parameter	STPSA42 Value	Unit
Transistor Type	NPN	—
Voltage - Collector Emitter Breakdown (Max)	300	V
Current - Collector (Ic) (Max)	500	mA
Power - Max	625	mW
Frequency - Transition	50	MHz
DC Current Gain (hFE) (Min) @ Ic, Vce	40 @ 30mA, 10V	—
Vce Saturation (Max) @ Ib, Ic	500mV @ 2mA, 20mA	—
Current - Collector Cutoff (Max)	100nA (ICBO)	—
Operating Temperature (Max)	150	°C
Mounting Type	Through Hole	—
Package / Case	TO-92-3	—

Substitute Part Grouping Explanation

Substitute parts for the STPSA42 are classified into two categories based on electrical parameter alignment:

Parametric Equivalents maintain identical or near-identical electrical specifications across all critical parameters: 300 V collector-emitter breakdown voltage, 500 mA maximum collector current, 625 mW power dissipation, 50 MHz transition frequency, 40 hFE minimum at specified bias conditions, and 500 mV saturation voltage at specified currents. These parts are direct functional replacements suitable for applications where the STPSA42 specifications are required.

Functional Alternatives provide similar electrical performance within acceptable operating ranges but may differ in one or more secondary parameters such as transition frequency, maximum operating temperature, or collector cutoff current. These parts are suitable for applications where the primary electrical requirements (voltage, current, power) are met, but secondary performance characteristics may vary.

The following parameters determine substitution eligibility:

Voltage - Collector Emitter Breakdown (Max): minimum 300 V
Current - Collector (Ic) (Max): minimum 500 mA
Power - Max: minimum 625 mW
DC Current Gain (hFE): minimum 40 at specified bias
Vce Saturation: maximum 500 mV at specified bias
Mounting Type: Through Hole
Package compatibility: TO-92-3 or TO-92 compatible

Parameter Comparison

Parameter	STPSA42	KSP42BU	MPSA42	MPSA42BK	ZTX657	2N6517BU	2N4401BU
Manufacturer	STMicroelectronics	onsemi	Diotec Semiconductor	Diotec Semiconductor	Diodes Incorporated	onsemi	onsemi
Transistor Type	NPN	NPN	NPN	NPN	NPN	NPN	NPN
Voltage - Collector Emitter Breakdown (Max)	300 V	300 V	300 V	300 V	300 V	350 V	40 V
Current - Collector (Ic) (Max)	500 mA	500 mA	500 mA	500 mA	500 mA	500 mA	600 mA
Power - Max	625 mW	625 mW	625 mW	625 mW	1 W	625 mW	625 mW
Frequency - Transition	50 MHz	50 MHz	50 MHz	50 MHz	30 MHz	200 MHz	250 MHz
DC Current Gain (hFE) (Min) @ Ic, Vce	40 @ 30mA, 10V	40 @ 30mA, 10V	40 @ 30mA, 10V	40 @ 30mA, 10V	50 @ 100mA, 5V	20 @ 50mA, 10V	100 @ 150mA, 1V
Vce Saturation (Max) @ Ib, Ic	500mV @ 2mA, 20mA	500mV @ 2mA, 20mA	500mV @ 2mA, 20mA	500mV @ 2mA, 20mA	500mV @ 10mA, 100mA	1V @ 5mA, 50mA	750mV @ 50mA, 500mA
Current - Collector Cutoff (Max)	100nA (ICBO)	100nA (ICBO)	100nA (ICBO)	100nA (ICBO)	100nA (ICBO)	50nA (ICBO)	—
Operating Temperature (Max)	150°C	150°C	150°C	150°C	200°C	150°C	150°C
Mounting Type	Through Hole	Through Hole	Through Hole	Through Hole	Through Hole	Through Hole	Through Hole
Package / Case	TO-92-3	TO-92-3	TO-92	TO-92	E-Line-3	TO-92-3	TO-92-3
Product Status	Obsolete	Active	Active	Active	Active	Last Time Buy	Active
RoHS Status	ROHS3 Compliant	ROHS3 Compliant	Not applicable	Not applicable	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant

Engineering Selection Recommendations

Primary Parametric Equivalents (Direct Replacements)

KSP42BU (onsemi) and MPSA42 / MPSA42BK (Diotec Semiconductor) are parametric equivalents to the STPSA42, maintaining identical electrical specifications across all critical parameters: 300 V breakdown voltage, 500 mA collector current, 625 mW power dissipation, 50 MHz transition frequency, and matching saturation voltage and current gain characteristics. KSP42BU is recommended as the primary substitute due to active product status and ROHS3 compliance. MPSA42 and MPSA42BK are available in higher inventory quantities and provide equivalent electrical performance; however, RoHS compliance status is not applicable for these parts.

Secondary Functional Alternative

ZTX657 (Diodes Incorporated) maintains the critical 300 V breakdown voltage and 500 mA collector current specifications with enhanced power dissipation capability (1 W versus 625 mW) and extended operating temperature range (-55°C to 200°C). The transition frequency is reduced to 30 MHz, which is acceptable for applications not requiring the full 50 MHz bandwidth of the STPSA42. ZTX657 is active and ROHS3 compliant. The E-Line-3 package is mechanically compatible with TO-92-3 footprints.

Not Recommended for Direct Substitution

2N6517BU exhibits reduced DC current gain (20 hFE minimum versus 40 minimum) and elevated saturation voltage (1 V versus 500 mV), making it unsuitable for applications requiring the STPSA42 gain and saturation characteristics. Product status is Last Time Buy, limiting long-term availability.

2N4401BU is not suitable due to insufficient collector-emitter breakdown voltage (40 V versus 300 V required), despite higher transition frequency and collector current capability. This part is designed for low-voltage applications and does not meet the voltage requirements of STPSA42-based circuits.

Frequently Asked Questions (FAQ)

Q: Can KSP42BU be used as a direct replacement for STPSA42 in all applications?

A: Yes. KSP42BU is a parametric equivalent with identical electrical specifications across all critical parameters: 300 V breakdown voltage, 500 mA collector current, 625 mW power dissipation, 50 MHz transition frequency, 40 hFE minimum, and 500 mV saturation voltage. The TO-92-3 package is mechanically and electrically compatible. KSP42BU is active and ROHS3 compliant.

Q: What is the difference between MPSA42 and MPSA42BK?

A: MPSA42 and MPSA42BK are electrically identical, both manufactured by Diotec Semiconductor with identical electrical specifications. The difference is packaging: MPSA42 is supplied in Cut Tape (CT) format, while MPSA42BK is supplied in Box format. Both are suitable for STPSA42 replacement. RoHS compliance status is not applicable for both variants.

Q: Why is ZTX657 listed as a secondary alternative rather than a primary equivalent?

A: ZTX657 maintains the critical 300 V breakdown voltage and 500 mA collector current specifications but differs in transition frequency (30 MHz versus 50 MHz) and package type (E-Line-3 versus TO-92-3). While the E-Line-3 package is mechanically compatible with TO-92-3 footprints, the reduced transition frequency makes it suitable only for applications where the full 50 MHz bandwidth is not required. ZTX657 offers enhanced power dissipation (1 W) and extended temperature range, making it advantageous for high-temperature or high-power applications.

Q: Is 2N4401BU a suitable substitute for STPSA42?

A: No. 2N4401BU has a maximum collector-emitter breakdown voltage of 40 V, which is insufficient for STPSA42 applications requiring 300 V operation. Although 2N4401BU offers higher transition frequency (250 MHz) and collector current (600 mA), the voltage limitation makes it unsuitable for direct substitution. 2N4401BU is designed for low-voltage applications and cannot be used in circuits designed for 300 V operation.

Q: What are the key parameters that determine STPSA42 substitution eligibility?

A: Substitution eligibility is determined by the following parameters: (1) Voltage - Collector Emitter Breakdown minimum 300 V, (2) Current - Collector (Ic) maximum minimum 500 mA, (3) Power dissipation minimum 625 mW, (4) DC Current Gain (hFE) minimum 40 at specified bias conditions, (5) Vce Saturation maximum 500 mV at specified bias, (6) Through Hole mounting type, and (7) TO-92-3 or TO-92 compatible package. Parts meeting all these criteria are direct parametric equivalents.

Q: Are there inventory considerations when selecting a substitute?

A: Yes. KSP42BU has the highest inventory availability (105,200 pcs), followed by MPSA42 (27,010 pcs) and MPSA42BK (20,778 pcs). ZTX657 has 9,300 pcs available. 2N6517BU (Last Time Buy status) has 20,200 pcs but is approaching end-of-life. For long-term production requirements, KSP42BU is recommended due to active status and highest inventory levels.

Q: Can ZTX657 be used in high-frequency applications requiring 50 MHz operation?

A: No. ZTX657 has a transition frequency of 30 MHz, which is below the STPSA42 specification of 50 MHz. For applications requiring 50 MHz or higher transition frequency, KSP42BU, MPSA42, or MPSA42BK are required. ZTX657 is suitable only for applications where the maximum required frequency is 30 MHz or lower.

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