KSC2518O Equivalent & Substitute Parts

Part Overview

The KSC2518O is an NPN Bipolar Junction Transistor (BJT) manufactured by onsemi, rated for 400 V collector-emitter breakdown voltage and 4 A maximum collector current in a TO-220-3 through-hole package. This device is classified as obsolete, indicating discontinued production and limited availability. Identifying equivalent and substitute parts is necessary to maintain design continuity, ensure supply chain reliability, and support ongoing production requirements for applications utilizing this transistor.

Key Parameters

Parameter	Value	Unit
Transistor Type	NPN	—
Voltage - Collector Emitter Breakdown (Max)	400	V
Current - Collector (Ic) (Max)	4	A
Power - Max	40	W
Vce Saturation (Max)	1 V @ 300mA, 1.5A	—
DC Current Gain (hFE) (Min)	30 @ 300mA, 5V	—
Operating Temperature (TJ)	150	°C
Mounting Type	Through Hole	—
Package / Case	TO-220-3	—

Substitute Part Grouping Explanation

Substitute parts for the KSC2518O are selected based on electrical and mechanical compatibility within the following criteria:

Primary Substitution Parameters:

Transistor Type: NPN (required match)
Voltage - Collector Emitter Breakdown: minimum 400 V (equal or higher acceptable)
Current - Collector (Ic) (Max): minimum 4 A (equal or higher acceptable)
Mounting Type: Through Hole (required match)
Package / Case: TO-220-3 or compatible TO-220 variants (required match)
Operating Temperature: 150°C (TJ) (required match)

Secondary Compatibility Factors:

Power dissipation rating of 40 W or higher
Vce saturation characteristics suitable for switching applications
DC current gain (hFE) characteristics appropriate for circuit design

Substitute parts meeting or exceeding these parameters in all categories are classified as direct equivalents. Parts with enhanced ratings (higher voltage, current, or power) are acceptable substitutes provided they maintain electrical compatibility with the original circuit design.

Parameter Comparison

Part Number	Manufacturer	Vce Breakdown (V)	Ic Max (A)	Power Max (W)	Vce Sat (Max)	hFE Min	Package	Status
KSC2518O	onsemi	400	4	40	1V @ 300mA, 1.5A	30 @ 300mA, 5V	TO-220-3	Obsolete
BUJD203A,127	WeEn Semiconductors	425	4	80	1V @ 600mA, 3A	11 @ 2A, 5V	TO-220-3	Active
BUL1102E	STMicroelectronics	450	4	70	1.5V @ 400mA, 2A	12 @ 2A, 5V	TO-220-3	Active
BUL128D-B	STMicroelectronics	400	4	70	500mV @ 1A, 4A	12 @ 2A, 5V	TO-220-3	Active
BUL38D	STMicroelectronics	450	5	80	1.1V @ 750mA, 3A	10 @ 10mA, 5V	TO-220-3	Active
BUL49D	STMicroelectronics	450	5	80	1.2V @ 800mA, 4A	4 @ 7A, 10V	TO-220-3	Active
BUL742C	STMicroelectronics	400	4	70	1.5V @ 1A, 3.5A	25 @ 800mA, 3V	TO-220-3	Active
ST13005	STMicroelectronics	400	4	75	1V @ 1A, 4A	8 @ 2A, 5V	TO-220-3	Active
TSC742CZ C0G	Taiwan Semiconductor Corporation	420	5	70	1.5V @ 1A, 3.5A	48 @ 100mA, 5V	TO-220-3	Active

Engineering Selection Recommendations

Direct Equivalents (Recommended Primary Substitutes):

The following parts provide direct electrical and mechanical compatibility with the KSC2518O and are classified as active products with current manufacturing status:

BUL128D-B (STMicroelectronics): Matches 400 V breakdown voltage and 4 A collector current specifications. RoHS3 compliant. Offers improved power rating (70 W vs. 40 W) and lower saturation voltage (500 mV vs. 1 V). Highest inventory availability among exact voltage/current matches.
BUL742C (STMicroelectronics): Matches 400 V breakdown voltage and 4 A collector current specifications. RoHS3 compliant. Provides 70 W power rating with hFE characteristics (25 @ 800mA, 3V) closer to the original device. Largest inventory stock (25,200 pcs).
ST13005 (STMicroelectronics): Matches 400 V breakdown voltage and 4 A collector current specifications. RoHS3 compliant. Offers 75 W power rating with improved saturation voltage (1 V @ 1A, 4A). Suitable for applications requiring enhanced thermal performance.

Secondary Substitutes (Enhanced Ratings):

The following parts exceed the KSC2518O specifications and are suitable for applications where higher voltage or current capability is beneficial:

BUJD203A,127 (WeEn Semiconductors): 425 V breakdown voltage, 4 A collector current, 80 W power rating. RoHS compliant. Provides voltage margin above the original 400 V specification.
BUL1102E (STMicroelectronics): 450 V breakdown voltage, 4 A collector current, 70 W power rating. RoHS3 compliant. Largest inventory availability (16,990 pcs) among all substitutes. Suitable for applications requiring higher voltage headroom.
BUL38D (STMicroelectronics): 450 V breakdown voltage, 5 A collector current, 80 W power rating. RoHS3 compliant. Provides both voltage and current enhancement over the original device.
TSC742CZ C0G (Taiwan Semiconductor Corporation): 420 V breakdown voltage, 5 A collector current, 70 W power rating. RoHS3 compliant. Offers highest DC current gain (hFE) at 48 @ 100mA, 5V, suitable for low-drive-current applications.

Compliance Status:

All substitute parts listed are RoHS3 compliant or RoHS compliant, ensuring regulatory compliance for new designs. The KSC2518O is classified as REACH Unaffected, and all substitute parts maintain REACH Unaffected status. All parts are classified under ECCN EAR99 and HTSUS 8541.29.0095.

Frequently Asked Questions (FAQ)

Q: Can I use a substitute part with higher voltage rating than the KSC2518O?

A: Yes. Substitute parts with voltage ratings equal to or higher than 400 V are electrically compatible. Higher voltage ratings provide additional design margin and do not compromise circuit functionality. Parts such as BUL1102E (450 V) and BUL38D (450 V) are suitable direct replacements.

Q: What is the difference between TO-220-3 and TO-220AB packaging?

A: Both are through-hole TO-220 variants with identical pin configurations and mechanical compatibility. TO-220AB is a specific supplier designation for the same package type. All substitute parts listed use compatible TO-220 packaging suitable for the KSC2518O footprint.

Q: Are substitute parts with higher current ratings (5 A vs. 4 A) compatible?

A: Yes. Substitute parts rated for 5 A collector current (such as BUL38D, BUL49D, and TSC742CZ C0G) are compatible with circuits designed for 4 A operation. The higher current rating provides additional design margin and does not affect circuit performance when operating at or below the original 4 A specification.

Q: Which substitute offers the best thermal performance?

A: ST13005 offers 75 W power dissipation rating, the highest among parts matching the original 400 V / 4 A specifications. BUL38D and BUL49D offer 80 W ratings but with higher current specifications (5 A). Selection depends on circuit thermal requirements and current demands.

Q: What is the significance of DC Current Gain (hFE) differences among substitutes?

A: DC Current Gain (hFE) affects base drive requirements and switching characteristics. The KSC2518O specifies hFE of 30 @ 300mA, 5V. Substitutes with lower hFE values (such as BUL38D at 10 @ 10mA, 5V) require higher base current for saturation. TSC742CZ C0G with hFE of 48 @ 100mA, 5V requires lower base drive. Circuit design must account for these differences in base current calculations.

Q: Is the KSC2518O still available for purchase?

A: The KSC2518O is classified as obsolete with limited inventory (1,090 pcs). All substitute parts listed are active products with significantly higher inventory availability, ranging from 673 to 25,200 units. Transition to an active substitute part is recommended for long-term supply chain reliability.

Q: Are all substitute parts RoHS compliant?

A: Yes. All substitute parts listed are either RoHS3 compliant or RoHS compliant, meeting current regulatory requirements. The KSC2518O is REACH Unaffected, and all substitutes maintain REACH Unaffected status, ensuring regulatory compliance for both legacy and new designs.

Q: Can I use BUL49D as a substitute if my circuit only requires 4 A operation?

A: Yes. BUL49D is rated for 5 A maximum collector current and is compatible with circuits designed for 4 A operation. However, note that BUL49D has lower DC Current Gain (hFE of 4 @ 7A, 10V) compared to the KSC2518O, requiring higher base drive current. Verify base drive circuit capability before selection.

Q: What is the inventory status of substitute parts?

A: BUL1102E has the highest inventory availability at 16,990 pcs. BUL742C has 25,200 pcs available. BUL38D has 8,725 pcs. ST13005 has 8,444 pcs. BUJD203A,127 has 673 pcs. BUL128D-B has 3,803 pcs. TSC742CZ C0G has 1,066 pcs. All substitutes have significantly higher availability than the obsolete KSC2518O.

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