HT32B DIAC Thyristor Equivalent & Substitute Parts

Part Overview

The HT32B is a DIAC (Diode for Alternating Current) thyristor manufactured by Littelfuse, rated for 30–34V breakover voltage with 2A peak output current in a DO-35 axial package. This component is classified as obsolete, making equivalent and substitute parts necessary for ongoing design support and production continuity. The HT32B serves in applications requiring precise voltage-triggered switching in AC circuits, commonly found in triac gate drive and phase control circuits.

Substiute Parts

HT32B

LittelfuseIn Stock: 740HT32B 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 DIAC thyristors is determined by three critical parameters: breakover voltage range, peak output current rating, and package compatibility. The HT32B operates within a 30–34V breakover window with 2A peak current in a DO-35 package.

Substitute parts are grouped into two categories based on breakover voltage alignment:

Category 1: Direct Voltage Match (30–34V) Parts with identical or overlapping breakover voltage specifications ensure drop-in compatibility without circuit redesign. These include DB3TG (STMicroelectronics, 30–34V) and the original HT32B specification.

Category 2: Extended Voltage Range (28–36V) Parts with wider breakover voltage windows that encompass the HT32B operating point. DB3 (Fairchild Semiconductor, 28–36V) falls into this category and remains functionally compatible provided the application tolerates the broader voltage window.

Category 3: Higher Voltage Rating (35–45V) DB4 (STMicroelectronics, 35–45V) operates outside the HT32B voltage specification and is not suitable as a direct substitute. This part is listed for reference only and should not be used as a replacement without circuit analysis.

All substitute candidates maintain identical peak output current (2A), operating temperature range (−40°C to +125°C), and DO-35 package format.

Parameter Comparison

Engineering Selection Recommendations

Preferred Substitute: DB3TG (STMicroelectronics)

DB3TG is the recommended substitute for HT32B applications. It provides exact voltage specification matching (30–34V), identical breakover current (15 µA), and active product status ensuring long-term availability. The part is ROHS3 compliant and available in Cut Tape packaging with 2,420 units in stock.

Alternative Substitute: DB3 (Fairchild Semiconductor)

DB3 is functionally compatible within the HT32B voltage operating point due to its 28–36V breakover range encompassing the 30–34V specification. However, DB3 carries obsolete product status, limiting future availability. Use only when DB3TG is unavailable and application requirements permit the wider voltage tolerance.

Not Recommended: DB4 (STMicroelectronics)

DB4 operates at 35–45V breakover voltage, outside the HT32B specification window. This part is unsuitable as a direct substitute and should not be used without circuit redesign and application analysis.

Frequently Asked Questions (FAQ)

Q: Can DB3 replace HT32B directly in production?

A: DB3 is functionally compatible because its 28–36V breakover range encompasses the HT32B 30–34V specification. However, DB3 is obsolete. DB3TG is the preferred choice for new designs and ongoing production due to active status and exact voltage matching.

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

A: Breakover voltage is the threshold voltage at which the DIAC switches on. Breakover current is the leakage current flowing through the device before switching occurs. Both parameters affect circuit timing and performance. HT32B and DB3TG share identical specifications for both parameters (30–34V, 15 µA).

Q: Why is DB4 listed if it cannot replace HT32B?

A: DB4 is included in the reference list because it shares the same package, peak current rating, and temperature range. However, its 35–45V breakover specification places it outside the HT32B operating window. DB4 is suitable only for applications requiring higher voltage triggering.

Q: Are all substitute parts available in DO-35 packaging?

A: Yes. HT32B, DB3, DB3TG, and DB4 are all available in DO-204AH/DO-35 axial package format, ensuring mechanical and electrical compatibility at the board level.

Q: What does ROHS3 compliance mean for this component?

A: ROHS3 compliance indicates the part meets Restriction of Hazardous Substances Directive requirements, restricting lead, cadmium, mercury, and other hazardous materials. All listed parts are ROHS3 compliant, suitable for applications with environmental and regulatory compliance requirements.

Q: Can I use DB3TG in place of HT32B without circuit modifications?

A: Yes. DB3TG provides exact parameter matching (30–34V breakover, 15 µA breakover current, 2A peak output, DO-35 package, −40°C to +125°C operating range). No circuit modifications are required for direct substitution.