ST-4-20 Equivalent & Substitute Parts Reference

Part Overview

The ST-4-20 is a laminated core power transformer manufactured by Signal Transformer, rated at 6VA with a 115V primary voltage and dual secondary windings capable of 10V parallel or 20V series output configurations. This through-hole mounted component is designed for applications requiring isolated AC power conversion with dual output flexibility. The part is currently in active production status with 983 units in stock inventory.

Equivalent and substitute parts are identified to provide procurement flexibility, ensure supply chain continuity, and support design requirements where the primary manufacturer part may be unavailable or where alternative sourcing is preferred.

Substiute Parts

ST-4-20

Signal TransformerIn Stock: 1041ST-4-20 Datasheet

Current PartRFQ

3FS-420

TamuraIn Stock: 11843FS-420 Datasheet

DirectRFQ

Key Parameters

Substitute Part Grouping Explanation

Substitute parts for the ST-4-20 are qualified based on strict electrical and mechanical parameter matching. The following criteria determine substitutability:

Electrical Parameters (Must Match):

• Primary voltage: 115V
• Secondary voltage configuration: Parallel 10V, Series 20V
• Secondary current capacity: Parallel 600mA, Series 300mA
• Power rating: 6VA
• Isolation voltage: 2500Vrms
• Core type: Laminated
• Winding configuration: Single primary, dual secondary

Mechanical Parameters (Must Match):

• Mounting type: Through Hole
• Termination style: PC Pin

Compliance Parameters (Must Match or Exceed):

• RoHS compliance status
• ECCN and HTSUS classifications

The 3FS-420 manufactured by Tamura meets all electrical and mechanical substitution criteria for the ST-4-20.

Parameter Comparison

Engineering Selection Recommendations

Both the ST-4-20 and 3FS-420 are active production components with full RoHS compliance and identical electrical specifications. Selection between these parts should be based on the following factors:

ST-4-20 (Signal Transformer):

• Primary choice for existing designs currently using this part number
• Box packaging suitable for component organization and traceability
• 983 units currently in stock inventory

3FS-420 (Tamura):

• Direct electrical and mechanical equivalent
• Tube packaging for high-volume manufacturing environments
• 1166 units currently in stock inventory
• Suitable for new designs or where Tamura supply chain is preferred

Physical dimensions of the 3FS-420 are within acceptable tolerance ranges for through-hole PCB mounting, with maximum height difference of 1.25mm. Both parts share identical electrical performance, isolation ratings, and compliance certifications.

Frequently Asked Questions (FAQ)

Q: Can the 3FS-420 be used as a direct replacement for the ST-4-20 in existing designs?

A: Yes. The 3FS-420 meets all electrical and mechanical specifications of the ST-4-20, including power rating, voltage outputs, current capacity, isolation voltage, mounting type, and termination style. Physical dimensions are within acceptable tolerance for through-hole PCB applications.

Q: What are the key differences between these two parts?

A: The primary differences are manufacturer (Signal Transformer vs. Tamura), packaging format (Box vs. Tube), and minor physical dimension variations (1.25mm maximum height difference). All electrical specifications and compliance certifications are identical.

Q: Are there any compliance or certification differences?

A: Both parts are RoHS compliant and share identical ECCN (EAR99) and HTSUS (8504.31.4035) classifications. The ST-4-20 carries RoHS3 certification while the 3FS-420 carries RoHS certification; both meet current regulatory requirements.

Q: How do the physical dimensions affect PCB layout?

A: The 3FS-420 has slightly larger dimensions (41.50mm L x 34.83mm W x 34.55mm H maximum) compared to the ST-4-20 (41.30mm L x 33.30mm W x 33.30mm H maximum). These differences are within standard PCB design tolerances for through-hole components and should not require layout modifications for typical applications.

Q: Which part should be selected for new designs?

A: Selection should be based on supply chain preference, packaging requirements, and inventory availability. Both parts are functionally equivalent and suitable for new designs. The 3FS-420 currently has higher inventory availability (1166 units vs. 983 units).

Q: What is the significance of the dual secondary winding configuration?

A: The dual secondary windings allow flexible output voltage selection: 10V at 600mA when windings are connected in parallel, or 20V at 300mA when connected in series. Both the ST-4-20 and 3FS-420 support identical winding configurations.