HT32 DIAC Thyristor - Equivalent & Substitute Parts

Part Overview

The HT32 is a DIAC (Diode for Alternating Current) thyristor manufactured by Littelfuse Inc., rated for 27–37V breakover voltage with 2A peak output current in DO-35 axial packaging. This component is classified as obsolete, making equivalent substitutes necessary for ongoing design support and procurement.

DIACs are bidirectional thyristors used primarily in AC switching applications, triac triggering circuits, and phase control applications. The HT32's voltage rating and current specifications define its functional role in these applications.

Key Parameters

Parameter	Value	Unit
Voltage - Breakover	27 – 37	V
Current - Breakover	15	µA
Current - Peak Output	2	A
Operating Temperature Range	–40 to +125	°C (TJ)
Package / Case	DO-204AH, DO-35, Axial	—
Product Status	Obsolete	—
RoHS Status	ROHS3 Compliant	—

Substitute Part Grouping Explanation

Substitution of DIAC thyristors is determined by three critical parameters: breakover voltage range, peak output current rating, and package type. All candidates must maintain the same DO-35 axial package and 2A peak current specification. Breakover voltage tolerance is the primary selection criterion; substitutes must operate within the voltage window required by the application circuit.

The HT32 specifies 27–37V breakover voltage. Substitute parts are grouped by their breakover voltage ranges:

DB3 (Fairchild Semiconductor): 28–36V breakover voltage — overlaps the HT32 range
DB3TG (STMicroelectronics): 30–34V breakover voltage — narrower range, centered within HT32 specification
DB4 (STMicroelectronics): 35–45V breakover voltage — higher voltage class, non-overlapping with HT32 lower range

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

Parameter Comparison

Parameter	HT32 (Littelfuse)	DB3 (Fairchild)	DB3TG (STMicroelectronics)	DB4 (STMicroelectronics)
Voltage - Breakover	27 – 37 V	28 – 36 V	30 – 34 V	35 – 45 V
Current - Breakover	15 µA	50 µA	15 µA	50 µA
Current - Peak Output	2 A	2 A	2 A	2 A
Operating Temperature	–40 to +125°C	–40 to +125°C	–40 to +125°C	–40 to +125°C
Package / Case	DO-35	DO-35	DO-35	DO-35
Product Status	Obsolete	Obsolete	Active	Active
RoHS Status	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant

Engineering Selection Recommendations

DB3TG (STMicroelectronics) is the primary substitute for HT32 applications. It matches the breakover current specification (15 µA), maintains identical peak output current (2A), and is currently in active production status. The 30–34V breakover range is centered within the HT32 specification window, providing optimal compatibility for circuits designed around the nominal HT32 voltage.

DB3 (Fairchild Semiconductor) provides voltage range overlap (28–36V) but operates at higher breakover current (50 µA). This part is obsolete; use only if existing inventory is available and circuit design accommodates the higher trigger current.

DB4 (STMicroelectronics) is suitable only for applications requiring higher breakover voltage (35–45V range). It is not a direct substitute for standard HT32 circuits operating in the 27–37V window.

All substitutes maintain RoHS3 compliance and identical operating temperature specifications, ensuring regulatory and thermal compatibility.

Frequently Asked Questions (FAQ)

Q: Can DB4 replace HT32 in my circuit? A: DB4 operates at 35–45V breakover voltage, which does not overlap the HT32 range of 27–37V. Use DB4 only if your application specifically requires higher breakover voltage. For standard HT32 circuits, select DB3 or DB3TG.

Q: What is the difference between DB3 and DB3TG? A: Both are DIAC thyristors in DO-35 packaging with 2A peak current. DB3TG matches the HT32 breakover current specification (15 µA) and is in active production. DB3 has higher breakover current (50 µA) and is obsolete. DB3TG is the preferred choice for new designs.

Q: Are all substitutes in the same package? A: Yes. HT32, DB3, DB3TG, and DB4 all use DO-35 axial packaging (DO-204AH), ensuring mechanical and electrical compatibility in existing PCB layouts.

Q: Does breakover current affect circuit operation? A: Breakover current determines the gate trigger sensitivity. HT32 and DB3TG both specify 15 µA, ensuring identical trigger behavior. DB3 and DB4 specify 50 µA, requiring higher trigger current. Select based on your circuit's trigger source capability.

Q: Are these parts RoHS compliant? A: Yes. HT32, DB3, DB3TG, and DB4 are all ROHS3 compliant, meeting environmental and regulatory requirements for current manufacturing standards.

Q: What is the operating temperature range? A: All substitutes operate from –40°C to +125°C (junction temperature), matching the HT32 specification. No thermal derating is required when substituting between these parts.

Request Quote (Ships tomorrow)

Part Number

Quantity

Company

Contact Name

E-mail

Message