STL128DN Equivalent & Substitute Parts

Part Overview

The STL128DN is a Bipolar (BJT) NPN transistor manufactured by STMicroelectronics, rated for 400 V collector-emitter breakdown voltage and 4 A maximum collector current in a TO-220 through-hole package. This device is classified as obsolete, making equivalent and substitute parts necessary for ongoing design support and procurement.

The STL128DN delivers 60 W maximum power dissipation with a saturation voltage of 1 V at 400 mA base current and 2 A collector current. The device operates at a maximum junction temperature of 150°C and maintains a minimum DC current gain (hFE) of 10 at 10 mA collector current and 5 V collector-emitter voltage.

Key Parameters

Parameter	Value	Unit
Transistor Type	NPN	—
Voltage - Collector Emitter Breakdown (Max)	400	V
Current - Collector (Ic) (Max)	4	A
Power - Max	60	W
Vce Saturation (Max) @ Ib, Ic	1 V @ 400 mA, 2 A	—
Current - Collector Cutoff (Max)	250	µA
DC Current Gain (hFE) (Min) @ Ic, Vce	10 @ 10 mA, 5 V	—
Operating Temperature (TJ)	150	°C
Mounting Type	Through Hole	—
Package / Case	TO-220-3	—
RoHS Status	ROHS3 Compliant	—
Moisture Sensitivity Level (MSL)	1 (Unlimited)	—

Substitute Part Grouping Explanation

Substitution of the STL128DN is determined by electrical and mechanical compatibility across the following critical parameters:

Primary Substitution Criteria:

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)
Package / Case: TO-220-3 (mechanical compatibility required)
Mounting Type: Through Hole (required match)

Secondary Compatibility Factors:

Power - Max: 60 W or higher (higher ratings provide design margin)
Operating Temperature: 150°C or higher (equal or higher acceptable)
RoHS Status: ROHS3 Compliant or equivalent (regulatory compliance)
Moisture Sensitivity Level: 1 (Unlimited) preferred for handling consistency

Substitute parts are grouped into two categories:

Category A - Direct Electrical Equivalents (4 A, 400 V): Parts meeting or exceeding the exact 4 A collector current and 400 V breakdown voltage specifications with compatible saturation characteristics.

Category B - Enhanced Performance Substitutes (5 A, 400-450 V): Parts with higher collector current ratings (5 A) and equal or higher breakdown voltages (400-450 V), providing increased current handling capacity and voltage margin while maintaining TO-220-3 package compatibility.

Parameter Comparison

Part Number	Manufacturer	Ic (Max) [A]	Vce Breakdown (Max) [V]	Power (Max) [W]	Vce Sat (Max) [V]	hFE (Min)	Package	Status
STL128DN	STMicroelectronics	4	400	60	1.0	10	TO-220-3	Obsolete
STL128D	STMicroelectronics	4	400	65	0.5	10	TO-220-3	Active
PHD13005,127	WeEn Semiconductors	4	400	75	1.0	10	TO-220-3	Active
BUJ302A,127	WeEn Semiconductors	4	400	80	1.5	25	TO-220-3	Active
FJP5555TU	Fairchild Semiconductor	5	400	75	1.5	20	TO-220-3	Active
BUL45D2G	onsemi	5	400	75	0.5	10	TO-220-3	Active
TSC742CZ C0G	Taiwan Semiconductor Corporation	5	420	70	1.5	48	TO-220-3	Active
KSC5338DTU	onsemi	5	450	75	0.5	6	TO-220-3	Last Time Buy
BUT11A	STMicroelectronics	5	450	83	1.5	10	TO-220-3	Obsolete

Engineering Selection Recommendations

For Direct Replacement (Minimum Design Change):

The STL128D from STMicroelectronics is the primary direct substitute. This part maintains identical electrical specifications (4 A, 400 V) while offering improved saturation characteristics (0.5 V versus 1.0 V) and higher power rating (65 W versus 60 W). The STL128D is in active production status, ensuring long-term availability. Both parts share the same base product number (STL128) and are ROHS3 compliant with MSL 1 (Unlimited) moisture sensitivity.

The PHD13005,127 from WeEn Semiconductors provides an alternative direct equivalent with identical electrical ratings and improved power dissipation (75 W). This part is in active production and maintains ROHS3 compliance with MSL 1 (Unlimited) handling characteristics.

For Enhanced Performance Applications:

The FJP5555TU from Fairchild Semiconductor and BUL45D2G from onsemi offer 5 A collector current capability at 400 V breakdown voltage, providing increased current margin. Both parts are in active production status and maintain ROHS3 compliance. The BUL45D2G includes transition frequency specification (13 MHz) and extended operating temperature range (−65°C to 150°C).

The TSC742CZ C0G from Taiwan Semiconductor Corporation provides 5 A at 420 V with active production status and ROHS3 compliance. This part features elevated DC current gain (hFE minimum of 48 at 100 mA, 5 V), which may require circuit design verification for applications sensitive to gain characteristics.

Avoid for New Designs:

The BUT11A and KSC5338DTU are classified as obsolete and last-time-buy respectively, limiting their suitability for long-term production applications despite meeting electrical specifications.

Frequently Asked Questions (FAQ)

Q: Can STL128D directly replace STL128DN without circuit modification?

A: Yes. The STL128D maintains identical collector current (4 A) and breakdown voltage (400 V) specifications with improved saturation voltage (0.5 V versus 1.0 V) and higher power rating (65 W versus 60 W). Both parts use TO-220-3 packaging and are ROHS3 compliant. No circuit modification is required.

Q: What is the difference between 4 A and 5 A rated substitutes?

A: The 5 A rated parts (FJP5555TU, BUL45D2G, TSC742CZ C0G, KSC5338DTU, BUT11A) provide higher collector current capacity. These parts are electrically compatible with the STL128DN in applications requiring 4 A or less, but offer increased current margin. All maintain TO-220-3 packaging and 400 V or higher breakdown voltage ratings.

Q: Are all substitute parts ROHS3 compliant?

A: All recommended active production substitutes (STL128D, PHD13005,127, BUJ302A,127, FJP5555TU, BUL45D2G, TSC742CZ C0G) are ROHS3 compliant. The KSC5338DTU is ROHS3 compliant but classified as last-time-buy. The BUT11A is ROHS3 compliant but obsolete.

Q: What is the significance of saturation voltage differences?

A: Saturation voltage (Vce Sat) affects power dissipation in switching applications. Lower saturation voltages reduce heat generation. The STL128D (0.5 V) and BUL45D2G (0.5 V) offer improved efficiency compared to the STL128DN (1.0 V). Applications with tight thermal budgets benefit from lower saturation voltage ratings.

Q: Can I use a higher voltage rated part (450 V) in place of the 400 V STL128DN?

A: Yes. Parts rated for 450 V breakdown voltage (KSC5338DTU, BUT11A) provide voltage margin and are electrically compatible with 400 V applications. The higher voltage rating does not degrade performance in 400 V circuits.

Q: What packaging considerations apply to these substitutes?

A: All substitute parts use TO-220-3 through-hole packaging, maintaining mechanical compatibility with STL128DN footprints. Verify PCB layout and thermal management provisions accommodate the specific part's power dissipation rating.

Q: Why is product status important for substitution selection?

A: Active production parts ensure long-term availability and consistent supply. Obsolete parts (STL128DN, BUT11A) face discontinuation risk. Last-time-buy parts (KSC5338DTU) have limited remaining inventory. For new designs and ongoing production, active status parts are preferred.

Q: Are there differences in moisture sensitivity handling?

A: Most substitutes maintain MSL 1 (Unlimited) rating, matching the STL128DN. The TSC742CZ C0G has MSL 3 (168 Hours), requiring more stringent moisture control during storage and handling. Parts with MSL 1 offer simpler logistics and storage requirements.

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