1N751A Zener Diode Equivalent & Substitute Parts

Part Overview

The 1N751A is a 5.1 V zener diode rated for 500 mW power dissipation in a DO-35 through-hole package. Manufactured by onsemi, this component is classified as obsolete. The 1N751A serves voltage regulation and protection applications requiring precise 5.1 V reference voltage with ±5% tolerance. Due to its obsolete status, equivalent and substitute parts from active manufacturers are necessary for new designs and ongoing production requirements.

Key Parameters

Parameter	Value	Unit
Voltage - Zener (Nom)	5.1	V
Tolerance	±5%	—
Power - Max	500	mW
Impedance (Max)	17	Ohms
Current - Reverse Leakage @ Vr	1	µA @ 1 V
Voltage - Forward (Vf) (Max) @ If	1.5	V @ 200 mA
Operating Temperature	-65 to 200	°C
Mounting Type	Through Hole	—
Package / Case	DO-204AH, DO-35, Axial	—

Substitute Part Grouping Explanation

Substitution of the 1N751A is determined by the following critical parameters:

Primary Matching Criteria:

Voltage - Zener (Nom): 5.1 V (exact match required)
Power - Max: 500 mW (exact match required)
Mounting Type: Through Hole (exact match required)
Package / Case: DO-35 or DO-204AH (exact match required)

Secondary Matching Criteria:

Tolerance: ±5% or tighter (±2% acceptable as upgrade)
Operating Temperature Range: -65°C minimum and 175°C or higher maximum
Impedance (Max): 17 Ohms or lower (lower values acceptable)

Substitute parts are grouped into three categories:

Direct Equivalents: Identical electrical specifications and tolerance to the 1N751A, with active product status from alternative manufacturers.
Parametric Equivalents: Tighter tolerance (±2%) or improved electrical characteristics while maintaining core voltage, power, and package specifications.
Similar Parts: Variations in secondary parameters such as impedance or reverse leakage current that remain functionally compatible within the application envelope.

Parameter Comparison

Part Number	Manufacturer	Vz (Nom)	Tolerance	Power (Max)	Zzt (Max)	Vf (Max) @ If	Temp Range	Product Status
1N751A	onsemi	5.1 V	±5%	500 mW	17 Ω	1.5 V @ 200 mA	-65 to 200°C	Obsolete
1N5231B	Microchip Technology	5.1 V	±5%	500 mW	17 Ω	1.5 V @ 200 mA	-65 to 175°C	Active
BZX79C5V1	Taiwan Semiconductor Corporation	5.1 V	±5%	500 mW	60 Ω	1.5 V @ 100 mA	-65 to 175°C	Active
1N5231C	Fairchild Semiconductor	5.1 V	±2%	500 mW	17 Ω	1.1 V @ 200 mA	-65 to 200°C	Active
1N751A	Microchip Technology	5.1 V	±5%	500 mW	17 Ω	1.1 V @ 200 mA	-65 to 175°C	Active
1N751A-1	Microchip Technology	5.1 V	±5%	500 mW	14 Ω	1.1 V @ 200 mA	-65 to 175°C	Active
1N751	Microchip Technology	5.1 V	±10%	400 mW	19 Ω	1.1 V @ 200 mA	-65 to 175°C	Active
1N751A TR PBFREE	Central Semiconductor Corp	5.1 V	±5%	500 mW	17 Ω	1.5 V @ 200 mA	-65 to 200°C	Active
1N751C	Microchip Technology	5.1 V	±2%	500 mW	17 Ω	1.1 V @ 200 mA	-65 to 175°C	Active
1N751C-1	Microchip Technology	5.1 V	±2%	500 mW	17 Ω	1.1 V @ 200 mA	-65 to 175°C	Active

Engineering Selection Recommendations

Direct Replacement (Identical Specifications):

The 1N5231B (Microchip Technology) and 1N751A TR PBFREE (Central Semiconductor Corp) are direct functional equivalents with active product status. Both maintain the 5.1 V nominal voltage, ±5% tolerance, 500 mW power rating, and DO-35 package. The 1N5231B operates to -65 to 175°C, while the 1N751A TR PBFREE extends to -65 to 200°C, matching the original 1N751A temperature range. The 1N751A TR PBFREE carries RoHS3 compliance certification.

Upgraded Tolerance Selection:

The 1N5231C (Fairchild Semiconductor), 1N751C (Microchip Technology), and 1N751C-1 (Microchip Technology) provide tighter ±2% tolerance compared to the original ±5% specification. These parts maintain identical 5.1 V voltage, 500 mW power, and DO-35 package. All three are active products with RoHS3 compliance. The 1N5231C and 1N751C variants operate to -65 to 200°C and -65 to 175°C respectively, providing improved voltage accuracy for precision regulation applications.

Active Manufacturer Alternatives:

The 1N751A (Microchip Technology) and 1N751A-1 (Microchip Technology) are active-status variants of the original part number. Both maintain core specifications with improved impedance characteristics (17 Ω and 14 Ω respectively) and lower forward voltage (1.1 V @ 200 mA). Operating temperature is -65 to 175°C.

Lower Power Alternative:

The 1N751 (Microchip Technology) is a similar part with reduced power rating (400 mW versus 500 mW) and wider tolerance (±10% versus ±5%). This part is suitable only for applications with lower power dissipation requirements.

Non-Standard Impedance Option:

The BZX79C5V1 (Taiwan Semiconductor Corporation) maintains 5.1 V voltage and 500 mW power but exhibits higher impedance (60 Ω versus 17 Ω). This part is RoHS3 compliant and active. Higher impedance may affect voltage regulation performance in low-impedance circuit configurations.

Frequently Asked Questions (FAQ)

Q: Can I substitute the 1N751A with any 5.1 V zener diode?

A: No. The substitute must match the 1N751A in nominal voltage (5.1 V), maximum power rating (500 mW), mounting type (through hole), and package (DO-35 or DO-204AH). Additional parameters such as tolerance, impedance, and operating temperature range must also be compatible with the application requirements.

Q: What is the difference between ±5% and ±2% tolerance zener diodes?

A: Tolerance specifies the allowable deviation of the zener voltage from its nominal value. A ±5% tolerance part allows the zener voltage to vary between 4.845 V and 5.355 V. A ±2% tolerance part restricts variation to 4.998 V and 5.202 V. Tighter tolerance (±2%) is suitable for precision voltage regulation applications where voltage accuracy is critical.

Q: Is the BZX79C5V1 a suitable replacement for the 1N751A?

A: The BZX79C5V1 matches the 1N751A in voltage (5.1 V), power (500 mW), and package (DO-35). However, it exhibits significantly higher impedance (60 Ω versus 17 Ω). Higher impedance results in greater voltage variation under load changes. This part is suitable only if the application tolerates higher output impedance and voltage regulation is not critical.

Q: Why do some substitute parts have a narrower operating temperature range?

A: Operating temperature range is determined by the manufacturer's design and qualification. The original 1N751A operates from -65 to 200°C. Many active substitutes operate to -65 to 175°C. If the application requires operation above 175°C, select the 1N5231C, 1N751A TR PBFREE, or 1N5231C which maintain the full -65 to 200°C range.

Q: What does "RoHS3 Compliant" mean?

A: RoHS3 (Restriction of Hazardous Substances Directive 3) compliance indicates the component does not contain restricted substances including lead, cadmium, mercury, hexavalent chromium, polybrominated biphenyls, or polybrominated diphenyl ethers. RoHS3 compliance is required for many applications, particularly in consumer electronics and European markets.

Q: Can I use the 1N751 (400 mW) instead of the 1N751A (500 mW)?

A: The 1N751 is suitable only if the application power dissipation does not exceed 400 mW. The 1N751 also carries wider tolerance (±10% versus ±5%), which may affect voltage regulation accuracy. Verify that both the power rating and tolerance are acceptable for the specific application before substitution.

Q: What is the significance of impedance (Zzt) in zener diode selection?

A: Impedance (Zzt) represents the dynamic resistance of the zener diode in its operating region. Lower impedance results in better voltage regulation and smaller voltage variations under load changes. The 1N751A specifies 17 Ω maximum impedance. Substitutes with equal or lower impedance maintain equivalent regulation performance.

Q: Are Microchip Technology 1N751A and 1N751A-1 interchangeable with the original onsemi 1N751A?

A: Both Microchip variants maintain the 5.1 V voltage, ±5% tolerance, 500 mW power, and DO-35 package. The Microchip 1N751A-1 offers improved impedance (14 Ω versus 17 Ω). However, the Microchip variants operate to -65 to 175°C, which is 25°C lower than the original onsemi part. Verify that the reduced upper temperature limit is acceptable for the application.

Q: What packaging options are available for 5.1 V 500 mW zener diodes?

A: All listed substitute parts are available in DO-35 through-hole axial package (DO-204AH designation). This is the standard package for this component category. No surface-mount alternatives are provided in this substitution list.

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