HT35RP DIAC Thyristor Equivalent & Substitute Parts

Part Overview

The HT35RP is a DIAC (Diode for Alternating Current) thyristor manufactured by Littelfuse Inc., designed for applications requiring bidirectional switching in AC circuits. Specified as a 30–40V breakover voltage device in DO-35 axial package, the HT35RP is classified as obsolete. Due to its obsolete status and limited availability relative to active alternatives, identifying equivalent substitute parts is essential for design continuity and procurement reliability.

Substiute Parts

HT35RP

Littelfuse Inc.In Stock: 810HT35RP Datasheet

Current PartRFQ

DB3

Fairchild SemiconductorIn Stock: 770983DB3 Datasheet

MFR RecommendedRFQ

DB3TG

STMicroelectronicsIn Stock: 2484DB3TG Datasheet

MFR RecommendedRFQ

DB4

STMicroelectronicsIn Stock: 20892DB4 Datasheet

MFR RecommendedRFQ

Key Parameters

Substitute Part Grouping Explanation

Substitution eligibility for the HT35RP is determined by the following critical parameters:

• Package Compatibility: All substitute parts must use DO-204AH / DO-35 axial package to ensure mechanical and electrical fit in existing PCB layouts.
• Voltage - Breakover Range: The HT35RP operates at 30–40V. Substitute parts must have breakover voltage ranges that overlap or fall within this specification window to maintain circuit functionality.
• Current - Peak Output: All candidates must support 2 A peak output current minimum.
• Operating Temperature Range: Substitute parts must support the full -40°C to 125°C operating range.
• Compliance: RoHS3 compliance is required for regulatory alignment.

Based on these criteria, three substitute parts are identified:

• DB3 (Fairchild Semiconductor): 28–36V breakover range overlaps the lower portion of HT35RP specification.
• DB3TG (STMicroelectronics): 30–34V breakover range is fully contained within HT35RP specification; active product status.
• DB4 (STMicroelectronics): 35–45V breakover range overlaps the upper portion of HT35RP specification.

Parameter Comparison

Engineering Selection Recommendations

DB3TG (STMicroelectronics) is the primary substitute candidate. It maintains the 30–34V breakover range within the HT35RP specification window, matches the 15 µA breakover current, and carries active product status with full RoHS3 compliance. This part provides the highest electrical alignment with the original HT35RP specification.

DB3 (Fairchild Semiconductor) is a secondary option where voltage tolerance permits operation in the 28–36V range. Note that this part is also obsolete and carries a higher breakover current (50 µA) compared to the HT35RP (15 µA).

DB4 (STMicroelectronics) is suitable only for applications where the higher 35–45V breakover range is acceptable. This part is active and RoHS3 compliant but operates at the upper voltage boundary of the HT35RP specification.

All three substitute parts maintain identical package geometry (DO-35), peak output current (2 A), and operating temperature range (-40°C to 125°C), ensuring mechanical and thermal compatibility.

Frequently Asked Questions (FAQ)

Q: Can DB3TG directly replace HT35RP in all applications?

A: DB3TG is electrically compatible where the 30–34V breakover range satisfies circuit requirements. Both parts share identical package (DO-35), peak current (2 A), and operating temperature (-40°C to 125°C). DB3TG is the preferred substitute due to active product status and specification alignment.

Q: What is the difference between DB3 and DB3TG?

A: Both are DIAC thyristors in DO-35 package with 2 A peak output. DB3 (Fairchild) has 28–36V breakover and 50 µA breakover current; DB3TG (STMicroelectronics) has 30–34V breakover and 15 µA breakover current. DB3TG more closely matches HT35RP electrical characteristics.

Q: When should DB4 be selected instead of DB3TG?

A: DB4 is appropriate only when circuit design requires the higher 35–45V breakover voltage range. Both DB4 and DB3TG are active products with RoHS3 compliance and identical package/current ratings.

Q: Are all substitute parts RoHS3 compliant?

A: Yes. HT35RP, DB3, DB3TG, and DB4 are all ROHS3 compliant, meeting regulatory requirements for lead-free and restricted substance standards.

Q: Does package compatibility affect substitution?

A: No. All parts use DO-204AH / DO-35 axial package. Mechanical fit and PCB layout compatibility are identical across HT35RP and all three substitute parts.