TOP257LG Equivalent & Substitute Parts

Part Overview

The TOP257LG is an offline switch flyback converter IC manufactured by Power Integrations, part of the TOPSwitch®-HX series. This component integrates a 700V breakdown voltage power switch with internal protection circuits for current limiting, over-temperature, and over-voltage conditions. The device operates at switching frequencies of 66kHz and 132kHz with a maximum power rating of 105W and 78% duty cycle.

The TOP257LG is classified as obsolete. Substitute parts from the active TOPSwitch®-HX product line provide equivalent or comparable functionality with current manufacturing support and availability.

Key Parameters

Parameter	TOP257LG
Manufacturer	Power Integrations
Series	TOPSwitch®-HX
Topology	Flyback
Output Isolation	Isolated
Voltage - Breakdown	700V
Frequency - Switching	66kHz, 132kHz
Power (Watts)	105W
Duty Cycle	78%
Fault Protection	Current Limiting, Over Temperature, Over Voltage
Operating Temperature	-40°C ~ 150°C (TJ)
Package / Case	7-SSIP, 6 Leads, Exposed Pad, Formed Leads
Supplier Device Package	eSIP-7F
Mounting Type	Through Hole
RoHS Status	RoHS Compliant
Moisture Sensitivity Level (MSL)	1 (Unlimited)
REACH Status	REACH Unaffected
Product Status	Obsolete

Substitute Part Grouping Explanation

Substitution within the TOPSwitch®-HX series is determined by the following critical parameters:

Fixed Parameters (Must Match):

Topology: Flyback
Output Isolation: Isolated
Voltage - Breakdown: 700V
Frequency - Switching: 66kHz, 132kHz
Duty Cycle: 78%
Fault Protection: Current Limiting, Over Temperature, Over Voltage
Operating Temperature: -40°C ~ 150°C (TJ)
Package / Case: 7-SSIP, 6 Leads, Exposed Pad, Formed Leads
Mounting Type: Through Hole
RoHS Status: RoHS Compliant
Moisture Sensitivity Level (MSL): 1 (Unlimited)
REACH Status: REACH Unaffected

Variable Parameter (Determines Substitution Suitability):

Power (Watts): Substitute parts range from 21W to 119W

The TOP257LG at 105W can be substituted with active TOPSwitch®-HX parts rated at equal or higher power output. Parts rated below 105W are not suitable as direct substitutes for this application.

Parameter Comparison

Part Number	Manufacturer	Series	Topology	Voltage - Breakdown	Frequency - Switching	Power (Watts)	Duty Cycle	Operating Temperature	Package	Product Status	Inventory (Pcs)
TOP257LG	Power Integrations	TOPSwitch®-HX	Flyback	700V	66kHz, 132kHz	105W	78%	-40°C ~ 150°C	7-SSIP eSIP-7F	Obsolete	1049
TOP252EG	Power Integrations	TOPSwitch®-HX	Flyback	700V	66kHz, 132kHz	21W	78%	-40°C ~ 150°C	7-SSIP eSIP-7C	Active	696
TOP252EN	Power Integrations	TOPSwitch®-HX	Flyback	700V	66kHz, 132kHz	21W	78%	-40°C ~ 150°C	7-SSIP eSIP-7C	Active	5100
TOP253EG	Power Integrations	TOPSwitch®-HX	Flyback	700V	66kHz, 132kHz	43W	78%	-40°C ~ 150°C	7-SSIP eSIP-7C	Active	677
TOP253EN	Power Integrations	TOPSwitch®-HX	Flyback	700V	66kHz, 132kHz	25W	78%	-40°C ~ 150°C	7-SSIP eSIP-7C	Active	1177
TOP254EG	Power Integrations	TOPSwitch®-HX	Flyback	700V	66kHz, 132kHz	62W	78%	-40°C ~ 150°C	7-SSIP eSIP-7C	Active	16400
TOP254EN	Power Integrations	TOPSwitch®-HX	Flyback	700V	66kHz, 132kHz	62W	78%	-40°C ~ 150°C	7-SSIP eSIP-7C	Active	3834
TOP255EG	Power Integrations	TOPSwitch®-HX	Flyback	700V	66kHz, 132kHz	81W	78%	-40°C ~ 150°C	7-SSIP eSIP-7C	Active	8000
TOP255EN	Power Integrations	TOPSwitch®-HX	Flyback	700V	66kHz, 132kHz	81W	78%	-40°C ~ 150°C	7-SSIP eSIP-7C	Active	10037
TOP256EG	Power Integrations	TOPSwitch®-HX	Flyback	700V	66kHz, 132kHz	119W	78%	-40°C ~ 150°C	7-SSIP eSIP-7C	Active	1266
TOP256EN	Power Integrations	TOPSwitch®-HX	Flyback	700V	66kHz, 132kHz	119W	78%	-40°C ~ 150°C	7-SSIP eSIP-7C	Active	27159

Engineering Selection Recommendations

Suitable Substitutes for TOP257LG (105W):

The TOP257LG can be replaced with the following active TOPSwitch®-HX parts that meet or exceed the 105W power requirement:

TOP256EG: 119W rated, active product status, 1266 units in stock
TOP256EN: 119W rated, active product status, 27159 units in stock

Both TOP256EG and TOP256EN maintain all critical electrical and mechanical parameters identical to the TOP257LG. The primary difference is the increased power rating (119W versus 105W), which provides design margin and ensures compatibility with the original application.

Not Suitable for Direct Substitution:

TOP252EG, TOP252EN, TOP253EG, TOP253EN, TOP254EG, and TOP254EN are rated below 105W and do not provide equivalent power handling capability for applications designed around the TOP257LG specification.

Compliance and Certification:

All recommended substitutes maintain:

RoHS Compliance
REACH Unaffected status
Moisture Sensitivity Level 1 (Unlimited)
Identical operating temperature range (-40°C ~ 150°C)
Through-hole mounting compatibility

Frequently Asked Questions (FAQ)

Q: Why is the TOP257LG obsolete?

A: The TOP257LG has been discontinued by Power Integrations. Active alternatives within the TOPSwitch®-HX series provide equivalent functionality with ongoing manufacturing support.

Q: Can I use a lower-power substitute like TOP254EN (62W) instead of TOP256EN (119W)?

A: No. The TOP257LG is rated at 105W. Substitutes must be rated at equal or higher power output. Using a lower-rated device would exceed its maximum power specification and create reliability risks.

Q: What is the difference between TOP256EG and TOP256EN?

A: Both parts are identical in electrical and mechanical specifications, including 119W power rating, 700V breakdown voltage, and 7-SSIP package. The difference lies in packaging format (Tube) and inventory availability. TOP256EN has significantly higher stock (27159 units versus 1266 units).

Q: Are the package dimensions identical between TOP257LG and TOP256EN?

A: Both use the 7-SSIP package with 6 leads, exposed pad, and formed leads. The supplier device package designation differs (eSIP-7F for TOP257LG versus eSIP-7C for TOP256EN), but both are through-hole mounted with identical lead configuration and PCB footprint compatibility.

Q: Do all substitutes maintain the same switching frequency?

A: Yes. All recommended substitutes operate at 66kHz and 132kHz switching frequencies, identical to the TOP257LG.

Q: Are there any temperature or environmental differences?

A: No. All substitutes maintain the identical operating temperature range of -40°C to 150°C (junction temperature) and carry the same RoHS and REACH compliance certifications.

Q: Which substitute should I select for new designs?

A: TOP256EN is recommended for new designs due to its active product status, highest inventory availability (27159 units), and 119W power rating that provides design margin above the original 105W specification.

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