KSA643YBU Equivalent & Substitute Parts

Part Overview

The KSA643YBU is a PNP bipolar junction transistor manufactured by onsemi, rated for 20 V collector-emitter breakdown voltage and 500 mA maximum collector current in a TO-92-3 through-hole package. This device is classified as obsolete, making equivalent and substitute parts necessary for ongoing design support and procurement continuity. The KSA643YBU serves applications requiring low-to-moderate current switching and amplification in consumer and industrial electronics.

Key Parameters

Parameter	Value	Unit
Transistor Type	PNP	—
Voltage - Collector Emitter Breakdown (Max)	20	V
Current - Collector (Ic) (Max)	500	mA
Power - Max	500	mW
Vce Saturation (Max)	400	mV @ 50mA, 500mA
DC Current Gain (hFE) (Min)	120	@ 100mA, 1V
Mounting Type	Through Hole	—
Package / Case	TO-92-3	—
Product Status	Obsolete	—

Substitute Part Grouping Explanation

Substitution of the KSA643YBU is determined by the following critical parameters:

Mandatory Matching Criteria:

Transistor Type: PNP
Voltage - Collector Emitter Breakdown (Max): 20 V minimum
Mounting Type: Through Hole
Package Compatibility: TO-92-3 or TO-92 compatible form factor

Performance Criteria:

Current - Collector (Ic) (Max): Equal to or greater than 500 mA
Power - Max: Equal to or greater than 500 mW
Vce Saturation: Lower values indicate improved switching performance

The substitute parts listed below meet or exceed the electrical specifications of the KSA643YBU while maintaining through-hole mounting compatibility. All substitutes are active products with current manufacturing status and full compliance certifications.

Parameter Comparison

Parameter	KSA643YBU (Main)	ZTX718	ZTX948	ZTX948STZ
Manufacturer	onsemi	Diodes Incorporated	Diodes Incorporated	Diodes Incorporated
Transistor Type	PNP	PNP	PNP	PNP
Voltage - Collector Emitter Breakdown (Max)	20 V	20 V	20 V	20 V
Current - Collector (Ic) (Max)	500 mA	2.5 A	4.5 A	4.5 A
Power - Max	500 mW	1 W	1.2 W	1.2 W
Vce Saturation (Max)	400 mV @ 50mA, 500mA	260 mV @ 200mA, 2.5A	310 mV @ 300mA, 5A	310 mV @ 300mA, 5A
DC Current Gain (hFE) (Min)	120 @ 100mA, 1V	150 @ 2A, 2V	100 @ 1A, 1V	100 @ 1A, 1V
Frequency - Transition	—	180 MHz	80 MHz	80 MHz
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)
Product Status	Obsolete	Active	Active	Active
RoHS Status	—	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant
Packaging	—	Bulk	Bulk	Tape & Box (TB)

Engineering Selection Recommendations

ZTX718 Selection: The ZTX718 is suitable for applications requiring moderate current capability (2.5 A) with improved switching performance. This device offers higher transition frequency (180 MHz) and lower saturation voltage (260 mV) compared to the KSA643YBU. The ZTX718 is active product status with ROHS3 compliance and unlimited moisture sensitivity rating. Use this substitute when higher frequency response is beneficial to circuit performance.

ZTX948 and ZTX948STZ Selection: Both ZTX948 variants provide the highest current capability (4.5 A) and power dissipation (1.2 W) among available substitutes. These devices are electrically identical with differences only in packaging format: ZTX948 is supplied in bulk packaging, while ZTX948STZ is supplied in tape and box format. Both are active products with ROHS3 compliance. Select these substitutes for applications requiring maximum current headroom or when higher power dissipation capability is required.

All substitute parts maintain the 20 V collector-emitter breakdown voltage rating and through-hole mounting compatibility with the KSA643YBU. All substitutes are active products with current manufacturing support and full compliance certifications, eliminating obsolescence risk associated with the original part.

Frequently Asked Questions (FAQ)

Q: Can ZTX718, ZTX948, and ZTX948STZ be used interchangeably with KSA643YBU?

A: Yes, within the constraints of circuit design. All three substitutes are PNP transistors with 20 V collector-emitter breakdown voltage and through-hole TO-92 compatible packaging. However, the higher current ratings (2.5 A and 4.5 A respectively) and improved saturation voltage characteristics mean they are direct upgrades in terms of electrical performance. Circuit design must account for these enhanced specifications.

Q: What is the difference between ZTX948 and ZTX948STZ?

A: ZTX948 and ZTX948STZ are electrically identical PNP transistors with identical electrical specifications. The difference is packaging format only: ZTX948 is supplied in bulk packaging, while ZTX948STZ is supplied in tape and box (TB) format. Select based on procurement and assembly requirements.

Q: Are all substitute parts RoHS compliant?

A: Yes. ZTX718, ZTX948, and ZTX948STZ are all ROHS3 compliant. The original KSA643YBU RoHS status is not specified in available documentation.

Q: What is the operating temperature range difference?

A: The KSA643YBU specifies a maximum junction temperature of 150°C. All substitute parts (ZTX718, ZTX948, ZTX948STZ) operate across -55°C to 200°C junction temperature range, providing wider thermal operating margin.

Q: Can I use a higher current-rated substitute in a circuit designed for 500 mA?

A: Yes. Higher current-rated devices operate safely at lower current levels. The ZTX718 (2.5 A) and ZTX948 variants (4.5 A) are direct substitutes for the 500 mA KSA643YBU. Circuit performance may improve due to lower saturation voltage and better thermal characteristics at reduced current levels.

Q: Are the substitute parts available in the same TO-92-3 package?

A: The substitute parts use E-Line-3 package format, which is TO-92 compatible. This means the physical form factor and pin configuration are compatible with TO-92-3 applications, allowing direct board-level substitution without layout modification.

Q: What is the moisture sensitivity level for all parts?

A: All parts, including the KSA643YBU and all substitutes (ZTX718, ZTX948, ZTX948STZ), have MSL 1 (Unlimited) rating, indicating no moisture sensitivity restrictions for storage and handling.

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