HT36B Equivalent & Substitute Parts

Part Overview

The HT36B is a DIAC thyristor manufactured by Littelfuse, rated for 34–38V breakover voltage with 2A peak output current in a DO-35 axial package. This component is classified as obsolete, making equivalent substitutes necessary for ongoing production and maintenance applications. DIAC thyristors function as bidirectional trigger devices in AC circuits, commonly used in triac gate drive and phase control applications. Substitute parts must maintain electrical compatibility within the specified voltage and current parameters while preserving the DO-35 package form factor.

Substiute Parts

HT36B

LittelfuseIn Stock: 1218HT36B 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 HT36B is determined by three critical parameters: breakover voltage range, peak output current rating, and package compatibility. All substitute parts must operate within the same DO-35 axial package and maintain the 2A peak output current specification. Breakover voltage tolerance is the primary selection criterion; substitutes are grouped by voltage overlap with the HT36B's 34–38V range.

The three qualified substitutes are:

• DB3 (Fairchild Semiconductor): 28–36V breakover range. Voltage overlap with HT36B is 34–36V.
• DB3TG (STMicroelectronics): 30–34V breakover range. Voltage overlap with HT36B is 34V (single-point intersection).
• DB4 (STMicroelectronics): 35–45V breakover range. Voltage overlap with HT36B is 35–38V.

All substitutes share identical peak output current (2A), operating temperature range (–40 to +125°C), package type (DO-35), and RoHS3 compliance with the main part.

Parameter Comparison

Engineering Selection Recommendations

DB3TG (STMicroelectronics) is the primary substitute for HT36B applications. This part carries active product status, ensuring long-term availability and supply chain stability. The 30–34V breakover range overlaps the HT36B at 34V, providing direct voltage compatibility at the upper tolerance boundary. Breakover current of 15µA matches the HT36B specification exactly, eliminating gate drive circuit redesign. ROHS3 compliance and REACH unaffected status confirm regulatory alignment.

DB4 (STMicroelectronics) is suitable for applications where the circuit can tolerate higher breakover voltage (35–45V range). This part offers the widest voltage margin within the HT36B's upper tolerance band (35–38V) and provides the highest inventory availability (20,830 pcs). Active product status ensures supply continuity. Breakover current of 50µA is higher than HT36B; gate drive circuits must be verified for compatibility with this parameter shift.

DB3 (Fairchild Semiconductor) provides voltage overlap (34–36V) but carries obsolete product status, limiting its suitability for new designs or long-term production. Breakover current of 50µA also requires gate drive circuit verification.

Frequently Asked Questions (FAQ)

Q: Can DB4 replace HT36B in all applications? A: DB4 is electrically compatible within the overlapping voltage range (35–38V). However, the higher breakover current (50µA vs. 15µA) may affect gate drive circuit performance. Circuit simulation or bench testing is necessary to confirm suitability for specific applications.

Q: Why is DB3TG recommended over DB3 despite similar voltage ranges? A: DB3TG carries active product status, ensuring availability and supply chain support. DB3 is obsolete, creating long-term sourcing risk. DB3TG also matches the HT36B breakover current specification (15µA), eliminating gate drive redesign requirements.

Q: Are all substitutes pin-compatible with HT36B? A: Yes. All substitutes use the DO-35 axial package with identical pinout and lead configuration. Direct mechanical and electrical substitution is possible without PCB modification.

Q: What is the significance of breakover current differences between parts? A: Breakover current determines the gate drive circuit's trigger threshold. HT36B and DB3TG both specify 15µA, requiring identical gate drive design. DB3 and DB4 specify 50µA, requiring higher trigger current and potentially different circuit component values.

Q: Are all substitutes RoHS3 compliant? A: Yes. HT36B, DB3, DB3TG, and DB4 all meet ROHS3 compliance requirements, confirming lead-free construction and environmental regulatory alignment.