HT32A DIAC Thyristor Equivalent & Substitute Parts

Part Overview

The HT32A is a DIAC (Diode for Alternating Current) thyristor manufactured by Littelfuse Inc., rated for 28–36V breakover voltage with 2A peak output current in DO-35 axial packaging. This component is classified as obsolete, making equivalent substitutes necessary for ongoing production and maintenance applications. The HT32A serves as a trigger device in AC control circuits, particularly in triac-based applications requiring precise voltage-triggered switching.

Substiute Parts

HT32A

Littelfuse Inc.In Stock: 1022HT32A 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 for the HT32A is determined by the following critical parameters:

Mandatory Compatibility Criteria:

• Package type: DO-204AH / DO-35 axial configuration (physical and electrical interface requirement)
• Peak output current: 2 A (functional requirement for load switching capacity)
• Operating temperature range: -40°C ~ 125°C (thermal operating envelope)
• RoHS3 compliance and MSL rating (regulatory and manufacturing compatibility)

Voltage Breakover Tolerance: The HT32A operates within 28–36V. Substitutes are grouped by their breakover voltage ranges:

• Direct substitutes (28–36V range): DB3 and DB3TG maintain the original voltage specification
• Higher voltage alternative (35–45V range): DB4 is suitable only for applications where the circuit design accommodates higher trigger voltage

All substitute parts maintain identical peak output current (2 A) and package configuration, ensuring mechanical and electrical interchangeability within their respective voltage classes.

Parameter Comparison

Engineering Selection Recommendations

Primary Substitutes (Direct Voltage Compatibility):

DB3TG (STMicroelectronics) is the preferred substitute. It maintains the 15 µA breakover current specification matching the HT32A, operates within the 30–34V range (subset of the original 28–36V specification), and carries active product status with ROHS3 compliance and REACH unaffected designation. This part ensures functional equivalence with current manufacturing support.

DB3 (Fairchild Semiconductor) provides full voltage range compatibility (28–36V) but operates at 50 µA breakover current, higher than the HT32A specification. This part is obsolete but remains available in high inventory. Selection of DB3 requires circuit validation to confirm that the elevated breakover current does not affect trigger timing or circuit performance.

Alternative Substitute (Higher Voltage Application):

DB4 (STMicroelectronics) is suitable only for applications where the circuit design accommodates 35–45V breakover voltage. This part is active, ROHS3 compliant, and carries REACH unaffected status. DB4 is not a direct substitute for the HT32A but may be applied in circuits designed for higher trigger voltage thresholds.

Compliance Considerations:

All substitute parts maintain ROHS3 compliance and MSL 1 rating, ensuring compatibility with modern manufacturing processes and storage requirements. DB3TG and DB4 carry REACH unaffected designation, providing additional regulatory assurance for European applications.

Frequently Asked Questions (FAQ)

Q: Can DB3 be used as a direct replacement for HT32A?

A: DB3 maintains the same voltage range (28–36V) and package configuration (DO-35), but operates at 50 µA breakover current compared to HT32A's 15 µA. Direct substitution is possible only if the circuit design tolerates the higher breakover current specification. Circuit validation is required.

Q: Why is DB3TG recommended over DB3?

A: DB3TG matches the HT32A breakover current specification (15 µA) and carries active product status with current manufacturing support. DB3 is obsolete and operates at higher breakover current (50 µA). DB3TG provides superior long-term availability and functional equivalence.

Q: Can DB4 replace HT32A in existing designs?

A: DB4 operates at 35–45V breakover voltage, above the HT32A specification of 28–36V. Substitution is not recommended for existing designs without circuit modification. DB4 is applicable only in applications specifically designed for higher trigger voltage thresholds.

Q: Are all substitutes available in DO-35 packaging?

A: Yes. HT32A, DB3, DB3TG, and DB4 are all available in DO-204AH / DO-35 axial package configuration, ensuring mechanical and electrical interface compatibility.

Q: What is the difference between breakover voltage and breakover current?

A: Breakover voltage is the AC voltage threshold at which the DIAC triggers and conducts. Breakover current is the leakage current flowing through the device before triggering occurs. Both parameters affect circuit timing and performance in AC control applications.

Q: Are all substitutes ROHS3 compliant?

A: Yes. HT32A, DB3, DB3TG, and DB4 are all ROHS3 compliant, meeting environmental and manufacturing standards for lead-free components.

Q: What is the significance of product status (Active vs. Obsolete)?

A: Active products have ongoing manufacturing support and guaranteed long-term availability. Obsolete products may have limited inventory and no future production. DB3TG and DB4 are active; HT32A and DB3 are obsolete. For new designs, active substitutes are preferred.