HT36A DIAC Thyristor Equivalent & Substitute Parts

Part Overview

The HT36A is a DIAC (Diode for Alternating Current) thyristor manufactured by Littelfuse Inc., rated for 32–40V breakover voltage with 2A peak output current in a DO-35 axial package. This component is classified as obsolete, making equivalent substitutes necessary for new designs and ongoing production support. The HT36A serves as a trigger device in AC control circuits, particularly in triac-based applications requiring precise voltage-triggered switching.

Substiute Parts

HT36A

Littelfuse Inc.In Stock: 1110HT36A 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 of the HT36A is determined by the following critical parameters:

• Package Compatibility: All substitutes must use DO-204AH / DO-35 axial packaging for mechanical and electrical interchangeability
• Voltage - Breakover Range: The substitute must operate within or overlap the 32–40V specification of the HT36A
• Current - Peak Output: Minimum 2A rating required to maintain circuit performance
• Operating Temperature Range: Must support -40°C to 125°C (TJ) for thermal compatibility
• RoHS Compliance: All substitutes must maintain ROHS3 compliance for regulatory alignment

The three qualified substitutes (DB3, DB3TG, DB4) meet these mechanical and electrical criteria. Selection depends on the specific breakover voltage requirement of the application circuit.

Parameter Comparison

Engineering Selection Recommendations

DB3TG (STMicroelectronics) is the primary substitute for new designs. It maintains active product status, ensuring long-term availability and supply chain stability. The 30–34V breakover range overlaps the HT36A specification with matching 15 µA breakover current, providing the closest electrical equivalence. DB3TG is supplied in Cut Tape (CT) packaging and carries REACH Unaffected status.

DB4 (STMicroelectronics) is suitable for applications requiring higher breakover voltage (35–45V). This part is active and widely available (20,830 pcs in stock). Use DB4 only when circuit design specifically calls for the elevated voltage threshold.

DB3 (Fairchild Semiconductor) is not recommended for new designs due to obsolete status, despite adequate electrical specifications (28–36V breakover). Existing inventory may support legacy product maintenance only.

Frequently Asked Questions (FAQ)

Q: Can DB3 directly replace HT36A in existing circuits? A: DB3 meets the mechanical (DO-35 package) and electrical (2A peak output, -40°C to 125°C) requirements. However, the 28–36V breakover range is lower than HT36A (32–40V), and the 50 µA breakover current differs from HT36A (15 µA). Verify circuit tolerance for these parameter variations before substitution.

Q: What is the difference between DB3TG and DB4? A: DB3TG has a 30–34V breakover voltage range, while DB4 operates at 35–45V. Both are active products with identical 2A peak output and DO-35 packaging. Select based on the specific breakover voltage requirement of your application circuit.

Q: Why is HT36A obsolete? A: The HT36A is listed as obsolete by Littelfuse Inc. Active alternatives from STMicroelectronics (DB3TG, DB4) and Fairchild Semiconductor (DB3) provide equivalent functionality with improved supply chain availability.

Q: Are all substitutes RoHS3 compliant? A: Yes. HT36A, DB3, DB3TG, and DB4 are all ROHS3 compliant, meeting regulatory requirements for new product designs and manufacturing.

Q: Does packaging differ between substitutes? A: All substitutes use DO-204AH / DO-35 axial packaging, identical to the HT36A. Physical and electrical pin compatibility is maintained across all four parts.

Q: What is the significance of breakover current (15 µA vs. 50 µA)? A: Breakover current determines the gate trigger sensitivity. HT36A and DB3TG both specify 15 µA, while DB3 and DB4 specify 50 µA. In gate-coupled triac circuits, higher breakover current may require increased gate drive. Verify circuit design tolerance before substitution.