FSL138MRTWDTU Equivalent & Substitute Parts

Part Overview

The FSL138MRTWDTU is an offline flyback converter IC manufactured by onsemi, designed for isolated power management applications. This device operates at 67kHz switching frequency with 50W power capability and integrates an internal switch for simplified circuit design. The FSL138MRTWDTU carries an Obsolete product status, making identification of equivalent and substitute parts essential for design continuity and procurement planning. Alternative components must maintain compatibility across isolation topology, voltage ratings, switching characteristics, and thermal performance parameters.

Substiute Parts

FSL138MRTWDTU

onsemiIn Stock: 1298FSL138MRTWDTU Datasheet

Current PartRFQ

NCP11185A065PG

onsemiIn Stock: 3413NCP11185A065PG Datasheet

MFR RecommendedRFQ

FSL136MRTWDTU

onsemiIn Stock: 2119FSL136MRTWDTU Datasheet

Parametric EquivalentRFQ

Key Parameters

Substitute Part Grouping Explanation

Substitute parts for the FSL138MRTWDTU are identified based on the following critical parameters that define functional equivalence:

Topology & Isolation: All substitutes must maintain isolated flyback topology to preserve circuit functionality and safety isolation requirements.

Voltage Ratings: Breakdown voltage and supply voltage ranges determine circuit compatibility. The FSL138MRTWDTU operates with 800V breakdown and 7.5V ~ 26V supply range.

Switching Characteristics: Frequency and duty cycle parameters affect transformer design and output filtering. The FSL138MRTWDTU operates at 67kHz with 67% duty cycle.

Power Capability: The 50W rating establishes the power handling envelope for substitute selection.

Thermal Performance: Operating temperature range (-40°C ~ 125°C) must be maintained or exceeded.

Package Compatibility: Through-hole mounting in TO-220-6 format is required for direct board-level substitution.

Fault Protection: Current limiting, overload, over-temperature, and over-voltage protection are baseline requirements.

Two substitute categories are identified:

MFR Recommended Substitute (NCP11185A065PG): Active product status with enhanced specifications including higher power rating (55W), extended temperature range (-40°C ~ 150°C), and additional fault protection features (open loop, short circuit). Package format differs (7-PDIP vs. TO-220-6), requiring circuit board redesign.

Parametric Equivalent (FSL136MRTWDTU): Same product family with identical package format (TO-220-6), switching frequency (67kHz), and duty cycle (67%). Voltage breakdown differs at 650V versus 800V, representing a reduced voltage rating within the same series.

Parameter Comparison

Engineering Selection Recommendations

NCP11185A065PG Selection: This substitute is the manufacturer-recommended option and carries Active product status, ensuring long-term availability and supply chain stability. The device provides enhanced specifications including 55W power capability, extended operating temperature range to 150°C, and comprehensive fault protection with open-loop and short-circuit detection. However, the 7-PDIP package format requires circuit board redesign compared to the original TO-220-6 footprint. The reduced startup voltage (2.1V vs. 12V) and narrower supply range (7.8V ~ 16V vs. 7.5V ~ 26V) necessitate circuit validation. The 65kHz switching frequency and 80% duty cycle differ from the original specification and may require transformer and filter component adjustments.

FSL136MRTWDTU Selection: This parametric equivalent maintains identical package format (TO-220-6), switching frequency (67kHz), and duty cycle (67%), minimizing circuit redesign requirements. Both devices share the same product family (FPS™ series) and identical supply voltage range (7.5V ~ 26V). The primary difference is reduced breakdown voltage (650V vs. 800V), which may be acceptable for applications with lower input voltage stress. Both devices carry Obsolete status, presenting equivalent long-term availability concerns. This option is suitable for direct board-level substitution when voltage rating reduction is acceptable.

All substitute options maintain ROHS3 compliance and REACH unaffected status, consistent with the original part.

Frequently Asked Questions (FAQ)

Q: Can NCP11185A065PG be used as a direct drop-in replacement for FSL138MRTWDTU?

A: No. While both devices maintain isolated flyback topology and 800V breakdown voltage, the NCP11185A065PG uses a 7-PDIP package format versus the TO-220-6 package of the FSL138MRTWDTU. Circuit board redesign is required. Additionally, the supply voltage range differs (7.8V ~ 16V vs. 7.5V ~ 26V), startup voltage is lower (2.1V vs. 12V), and switching frequency is 65kHz versus 67kHz. These differences require circuit validation and component adjustments.

Q: Is FSL136MRTWDTU a suitable alternative for the FSL138MRTWDTU?

A: FSL136MRTWDTU is a parametric equivalent within the same product family. It maintains identical TO-220-6 package format, 67kHz switching frequency, 67% duty cycle, and 7.5V ~ 26V supply range. The primary difference is reduced breakdown voltage (650V vs. 800V). This substitute is suitable for applications where the lower voltage rating is acceptable and direct board-level substitution is required.

Q: What are the key differences in fault protection between these devices?

A: The FSL138MRTWDTU and FSL136MRTWDTU provide identical fault protection: current limiting, overload, over-temperature, and over-voltage. The NCP11185A065PG adds open-loop and short-circuit protection, providing enhanced fault detection capabilities.

Q: Why does the NCP11185A065PG have a lower startup voltage?

A: The NCP11185A065PG startup voltage is 2.1V compared to 12V for the FSL138MRTWDTU. This parameter is determined by the internal circuit design and control architecture of each device. Lower startup voltage may affect circuit behavior during power-up sequences and requires validation in the target application.

Q: Are all three devices RoHS3 compliant?

A: Yes. FSL138MRTWDTU, NCP11185A065PG, and FSL136MRTWDTU are all ROHS3 compliant and REACH unaffected, meeting current environmental and regulatory requirements.

Q: What is the impact of different switching frequencies on circuit design?

A: The FSL138MRTWDTU and FSL136MRTWDTU operate at 67kHz, while the NCP11185A065PG operates at 65kHz. Switching frequency determines transformer core selection, output filter design, and electromagnetic interference characteristics. Frequency differences of 2kHz are minor but may require transformer and filter component recalculation for the NCP11185A065PG.

Q: Can the duty cycle difference between devices affect circuit performance?

A: Yes. The FSL138MRTWDTU and FSL136MRTWDTU operate at 67% duty cycle, while the NCP11185A065PG operates at 80%. Duty cycle affects transformer design, output voltage regulation, and power transfer characteristics. The 13% difference requires transformer recalculation and circuit validation for the NCP11185A065PG.