BZX85C51 Equivalent & Substitute Parts

Part Overview

The BZX85C51 is a through-hole zener diode rated at 51 V nominal voltage with 1 W maximum power dissipation, manufactured by onsemi in the DO-41 package. This component is classified as obsolete, indicating that onsemi has discontinued production. Equivalent and substitute parts are necessary to maintain design continuity and ensure component availability for new production runs, repairs, and system upgrades.

Key Parameters

Parameter	Value	Unit
Voltage - Zener (Nom)	51	V
Tolerance	±6%	—
Power - Max	1	W
Impedance (Max)	115	Ohms
Current - Reverse Leakage @ Vr	500 nA @ 36 V	—
Voltage - Forward (Vf) (Max) @ If	1.2 V @ 200 mA	—
Operating Temperature	-65°C to 200°C	—
Mounting Type	Through Hole	—
Package / Case	DO-204AL, DO-41, Axial	—

Substitute Part Grouping Explanation

Substitution of the BZX85C51 is determined by the following critical parameters:

Voltage - Zener (Nom): Must be 51 V
Power - Max: Must be 1 W
Mounting Type: Must be Through Hole
Package / Case: Must be DO-41 or DO-204AL (equivalent designations)

All substitute parts listed maintain these core electrical and mechanical specifications. Variations in tolerance (±2%, ±5%, ±10%), impedance, reverse leakage current, and operating temperature range are secondary parameters that do not prevent functional substitution but may affect circuit performance characteristics. Packaging format (Bulk or Tape & Reel) and product status (Active vs. Obsolete) are logistical considerations that do not affect electrical compatibility.

Parameter Comparison

Part Number	Manufacturer	Vz (Nom)	Tolerance	Power (Max)	Zzt (Max)	Vf (Max) @ If	Temp Range	Package	Status
BZX85C51	onsemi	51 V	±6%	1 W	115 Ω	1.2 V @ 200 mA	-65°C to 200°C	DO-41	Obsolete
1N4757A	Fairchild Semiconductor	51 V	±5%	1 W	95 Ω	1.2 V @ 200 mA	-65°C to 175°C	DO-41	Active
1N3037B-1	Microchip Technology	51 V	±5%	1 W	95 Ω	1.2 V @ 200 mA	-55°C to 175°C	DO-41	Active
1N4757AP/TR12	Microchip Technology	51 V	±5%	1 W	95 Ω	1.2 V @ 200 mA	-65°C to 150°C	DO-41	Active
1N4757CE3/TR13	Microchip Technology	51 V	±2%	1 W	95 Ω	1.2 V @ 200 mA	-65°C to 150°C	DO-41	Active
1N4757CP/TR12	Microchip Technology	51 V	±2%	1 W	95 Ω	1.2 V @ 200 mA	-65°C to 150°C	DO-41	Active
1N4757CP/TR8	Microchip Technology	51 V	±2%	1 W	95 Ω	1.2 V @ 200 mA	-65°C to 150°C	DO-41	Active
1N4757CPE3/TR12	Microchip Technology	51 V	±2%	1 W	95 Ω	1.2 V @ 200 mA	-65°C to 150°C	DO-41	Active
1N4757CPE3/TR8	Microchip Technology	51 V	±2%	1 W	95 Ω	1.2 V @ 200 mA	-65°C to 150°C	DO-41	Active
1N4757P/TR12	Microchip Technology	51 V	±10%	1 W	95 Ω	1.2 V @ 200 mA	-65°C to 150°C	DO-41	Active
1N4757P/TR8	Microchip Technology	51 V	±10%	1 W	95 Ω	1.2 V @ 200 mA	-65°C to 150°C	DO-41	Active

Engineering Selection Recommendations

All listed substitute parts are electrically and mechanically compatible with the BZX85C51 based on matching nominal zener voltage (51 V), maximum power rating (1 W), and through-hole DO-41 package configuration.

Active Product Status: All substitute parts carry Active product status, ensuring long-term availability and continued manufacturing support. The BZX85C51 is Obsolete and no longer produced by onsemi.

Tolerance Considerations: The BZX85C51 specifies ±6% tolerance. Substitute parts with tighter tolerances (±2% or ±5%) provide improved voltage regulation accuracy. Substitute parts with wider tolerance (±10%) are functionally compatible but offer less precise voltage regulation.

Impedance: Substitute parts from Microchip Technology and Fairchild Semiconductor specify 95 Ω maximum impedance, compared to 115 Ω for the BZX85C51. Lower impedance improves transient response and voltage stability.

Operating Temperature Range: The BZX85C51 operates from -65°C to 200°C. Most substitute parts operate from -65°C to 150°C, which is suitable for standard industrial and commercial applications. The 1N3037B-1 operates from -55°C to 175°C. Applications requiring operation above 150°C require verification against specific circuit requirements.

RoHS Compliance: The 1N4757CE3/TR13 and 1N4757CPE3/TR12 and 1N4757CPE3/TR8 variants are ROHS3 Compliant. Other variants are RoHS non-compliant. Select ROHS3-compliant variants for applications subject to RoHS regulations.

Packaging Format: Bulk packaging is suitable for manual assembly and repair. Tape & Reel (TR) packaging is optimized for automated pick-and-place assembly. TR12 and TR8 designations indicate reel quantities per 12-inch and 8-inch reels respectively.

Frequently Asked Questions (FAQ)

Q: Can I directly replace BZX85C51 with any of the listed substitute parts?

A: Yes. All listed substitute parts maintain the critical electrical parameters (51 V nominal zener voltage, 1 W maximum power) and mechanical specifications (through-hole DO-41 package) required for direct substitution. Differences in tolerance, impedance, and temperature range do not prevent functional replacement but may affect circuit performance characteristics.

Q: What is the difference between 1N4757A, 1N4757AP/TR12, and 1N4757P/TR12?

A: These parts share the same base part number (1N4757) but differ in tolerance and packaging. The 1N4757A has ±5% tolerance in Bulk packaging. The 1N4757AP/TR12 has ±5% tolerance in Tape & Reel format. The 1N4757P/TR12 has ±10% tolerance in Tape & Reel format. All three are electrically equivalent for applications not requiring tight voltage regulation.

Q: Why do some parts have ±2% tolerance while others have ±10%?

A: Tolerance reflects the manufacturing precision of the zener voltage. Tighter tolerance (±2%) provides more accurate voltage regulation but typically at higher cost. Wider tolerance (±10%) is suitable for applications where voltage regulation precision is less critical. Select tolerance based on circuit requirements.

Q: What does the TR12 or TR8 designation mean?

A: TR indicates Tape & Reel packaging format for automated assembly. TR12 specifies 12-inch reel quantity, while TR8 specifies 8-inch reel quantity. These designations do not affect electrical performance; they indicate packaging and quantity per reel for procurement purposes.

Q: Is the 1N3037B-1 suitable for applications requiring -65°C operation?

A: The 1N3037B-1 operates from -55°C to 175°C, which does not include -65°C. For applications requiring -65°C minimum operating temperature, select substitute parts with -65°C lower temperature limit, such as 1N4757A, 1N4757AP/TR12, or the 1N4757 variants with CE3, CP, or P designations.

Q: Are ROHS3-compliant variants required for my application?

A: ROHS3 compliance is required for products sold in the European Union and other regions with RoHS regulations. If your application is subject to RoHS requirements, select 1N4757CE3/TR13, 1N4757CPE3/TR12, or 1N4757CPE3/TR8. For applications without RoHS requirements, non-compliant variants are acceptable.

Q: What is the difference between DO-204AL and DO-41 package designations?

A: DO-204AL and DO-41 are equivalent package designations for the same through-hole axial lead diode package. Both refer to the same physical form factor and pin configuration. These designations are interchangeable.

Q: Can I use 1N4757P/TR8 in place of BZX85C51 in a precision voltage reference circuit?

A: The 1N4757P/TR8 has ±10% tolerance, which is wider than the BZX85C51's ±6% tolerance. For precision voltage reference applications, select substitute parts with tighter tolerance such as 1N4757CE3/TR13 or 1N4757CPE3/TR8 (±2% tolerance) to maintain circuit accuracy.

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