1N975B Zener Diode Equivalent & Substitute Parts

Part Overview

The 1N975B is a 39 V, 500 mW Zener diode manufactured by onsemi in a DO-35 axial through-hole package. This component is classified as obsolete, necessitating identification of active equivalent and substitute parts for ongoing design requirements. The 1N975B serves voltage regulation and protection applications requiring a nominal Zener voltage of 39 V with ±5% tolerance and 500 mW maximum power dissipation. Active substitute parts maintain the core electrical specifications while offering improved availability and, in some cases, enhanced performance characteristics or compliance certifications.

Key Parameters

Parameter	1N975B Specification
Voltage - Zener (Nom) (Vz)	39 V
Tolerance	±5%
Power - Max	500 mW
Impedance (Max) (Zzt)	80 Ohms
Current - Reverse Leakage @ Vr	5 µA @ 29.7 V
Operating Temperature	-65°C ~ 200°C
Mounting Type	Through Hole
Package / Case	DO-204AH, DO-35, Axial
Product Status	Obsolete

Substitute Part Grouping Explanation

Substitution of the 1N975B is determined by strict adherence to the following electrical and mechanical parameters:

Primary Substitution Criteria:

Voltage - Zener (Nom) (Vz): 39 V (exact match required)
Tolerance: ±5% or tighter (±10% acceptable for lower-precision applications)
Mounting Type: Through Hole (axial configuration)
Current - Reverse Leakage @ Vr: 5 µA or lower at specified reverse voltage

Secondary Substitution Criteria:

Power - Max: 500 mW or greater (higher power ratings provide design margin)
Impedance (Max) (Zzt): 80 Ohms or lower (lower impedance improves regulation)
Operating Temperature: Must encompass or exceed -65°C ~ 200°C range
Package / Case: DO-35, DO-41, or T-18 axial packages (mechanical compatibility with through-hole mounting)

Substitute parts are grouped into three categories based on power rating: 500 mW (direct replacement), 1 W to 1.5 W (moderate upgrade), and 5 W (high-power upgrade). All substitute parts maintain the 39 V nominal Zener voltage and ±5% tolerance specification.

Parameter Comparison

Part Number	Manufacturer	Vz (Nom)	Tolerance	Power - Max	Zzt (Max)	Leakage @ Vr	Temp Range	Package	Status
1N975B	onsemi	39 V	±5%	500 mW	80 Ω	5 µA @ 29.7 V	-65°C ~ 200°C	DO-35	Obsolete
1N975B-1	Microchip Technology	39 V	±5%	500 mW	80 Ω	500 nA @ 30 V	-65°C ~ 175°C	DO-35	Active
1N975A	Microchip Technology	39 V	±10%	500 mW	80 Ω	5 µA @ 29.7 V	-65°C ~ 175°C	DO-7	Active
1EZ39D5-TP	Micro Commercial Co	39 V	±5%	1 W	60 Ω	5 µA @ 29.7 V	-55°C ~ 150°C	DO-41	Active
1N4754A	Lumimax Optoelectronic Technology	39 V	±5%	1 W	60 Ω	5 µA @ 29.7 V	-65°C ~ 200°C	DO-41	Active
1N5939BP-TP	Micro Commercial Co	39 V	±5%	1.5 W	45 Ω	1 µA @ 29.7 V	-55°C ~ 175°C	DO-41	Active
2EZ39D5-AP	Micro Commercial Co	39 V	±5%	2 W	30 Ω	500 nA @ 29.7 V	-55°C ~ 150°C	DO-41	Active
1N5366B	Microsemi Corporation	39 V	±5%	5 W	14 Ω	500 nA @ 28.1 V	-65°C ~ 150°C	T-18	Active

Engineering Selection Recommendations

Direct Replacement (500 mW Power Rating):

The 1N975B-1 manufactured by Microchip Technology is the primary direct replacement. It maintains identical electrical specifications (39 V, ±5%, 500 mW, 80 Ω impedance) and package configuration (DO-35). The 1N975B-1 is active with ROHS3 compliance and demonstrates superior reverse leakage characteristics (500 nA versus 5 µA). Operating temperature range is -65°C ~ 175°C, which covers the majority of industrial applications, though it does not extend to the original 200°C maximum.

The 1N975A is an alternative direct replacement from Microchip Technology with identical power and impedance specifications. However, it features ±10% tolerance (versus ±5%) and uses a DO-7 package instead of DO-35, requiring PCB layout modification.

Upgraded Substitutes (1 W to 1.5 W Power Rating):

The 1N4754A (Lumimax) and 1EZ39D5-TP (Micro Commercial Co) both provide 1 W power dissipation with improved impedance (60 Ω) and maintain ±5% tolerance. The 1N4754A extends the operating temperature range to -65°C ~ 200°C, matching the original specification. Both use DO-41 packages, requiring mechanical accommodation.

The 1N5939BP-TP (Micro Commercial Co) offers 1.5 W power with further reduced impedance (45 Ω) and superior reverse leakage (1 µA). ROHS3 compliance is confirmed. Operating temperature is -55°C ~ 175°C.

High-Power Substitute (5 W Power Rating):

The 1N5366B (Microsemi Corporation) provides 5 W dissipation with significantly reduced impedance (14 Ω), delivering superior voltage regulation performance. Reverse leakage is 500 nA. The T-18 package requires mechanical redesign. Operating temperature is -65°C ~ 150°C.

Compliance Considerations:

The 1N975B-1, 1N4754A, 1N5939BP-TP, and 2EZ39D5-AP carry active product status with current manufacturing support. The 1N5366B is RoHS non-compliant; applications requiring RoHS compliance should select 1N975B-1, 1N4754A, or 1N5939BP-TP.

Frequently Asked Questions (FAQ)

Q: Can the 1N975B-1 be used as a direct replacement for the 1N975B?

A: Yes. The 1N975B-1 maintains identical electrical specifications (39 V, ±5%, 500 mW, 80 Ω) and uses the same DO-35 package. No PCB modification is required. The 1N975B-1 is active and carries ROHS3 compliance.

Q: What is the difference between DO-35 and DO-41 packages?

A: Both are axial through-hole packages for Zener diodes. DO-35 (DO-204AH) is a smaller diameter package used in the 1N975B and 1N975B-1. DO-41 (DO-204AL) is a larger diameter package used in 1W and higher power ratings. Substitution between these packages requires PCB layout modification to accommodate different lead spacing and body dimensions.

Q: Can I use a 1 W Zener diode (1N4754A) in place of the 500 mW 1N975B?

A: Yes, with mechanical accommodation. The 1N4754A maintains the 39 V nominal voltage and ±5% tolerance. The higher power rating (1 W versus 500 mW) provides design margin and improved thermal performance. However, the DO-41 package requires PCB modification compared to the DO-35 package of the 1N975B.

Q: What does impedance (Zzt) mean, and why does it matter?

A: Impedance (Zzt) is the dynamic impedance of the Zener diode in the reverse-biased region. Lower impedance indicates better voltage regulation performance and reduced voltage ripple. The 1N975B has 80 Ω impedance. Substitute parts with lower impedance (such as 1N5366B at 14 Ω) provide superior regulation but require higher power dissipation capability.

Q: Is the 1N975A a suitable replacement?

A: The 1N975A is functionally compatible but has two limitations: ±10% tolerance (versus ±5%) and a DO-7 package (versus DO-35). Applications requiring ±5% tolerance should use 1N975B-1 instead. The DO-7 package requires PCB modification.

Q: Why do some substitute parts have lower reverse leakage current?

A: Reverse leakage current (specified at a given reverse voltage) indicates the quality of the diode junction. Lower leakage (such as 500 nA versus 5 µA) represents improved manufacturing processes and tighter quality control. This does not affect substitution compatibility but indicates superior device characteristics.

Q: Can I use the 1N5366B (5 W) in a circuit designed for the 1N975B (500 mW)?

A: Yes, electrically. The 1N5366B maintains 39 V nominal voltage and ±5% tolerance. The significantly higher power rating and lower impedance (14 Ω) provide superior performance. However, the T-18 package is substantially larger and requires PCB redesign. Additionally, the 1N5366B is RoHS non-compliant.

Q: What is the operating temperature range, and does it affect substitution?

A: The 1N975B operates from -65°C to 200°C. Most substitute parts operate from -55°C to 175°C or -65°C to 150°C. For applications requiring the full -65°C to 200°C range, the 1N4754A is the only substitute that matches this specification. For applications within -55°C to 175°C, all listed substitutes are suitable.

Q: Are all substitute parts RoHS compliant?

A: No. The 1N5366B is RoHS non-compliant. The 1N975B-1, 1N4754A, 1N5939BP-TP, and 2EZ39D5-AP carry ROHS3 compliance. Applications requiring RoHS compliance must exclude the 1N5366B.

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