MR851 Equivalent & Substitute Parts Reference

Part Overview

The MR851 is a general-purpose rectifier diode manufactured by onsemi, rated for 100 V DC reverse voltage and 3 A average rectified current in an axial through-hole package. The MR851 is classified as obsolete product status. Identification of equivalent and substitute parts is necessary to maintain design continuity and ensure component availability for new production runs, repairs, and legacy system support.

Key Parameters

Parameter	Value	Unit
Voltage - DC Reverse (Vr) (Max)	100	V
Current - Average Rectified (Io)	3	A
Voltage - Forward (Vf) (Max) @ If	1.25 V @ 3 A	V
Speed	Fast Recovery ≤ 500ns, > 200mA (Io)	—
Reverse Recovery Time (trr)	300	ns
Current - Reverse Leakage @ Vr	10	µA @ 100 V
Mounting Type	Through Hole	—
Package / Case	DO-201AA, DO-27, Axial	—
Operating Temperature - Junction	-65 to 125	°C
Technology	Standard	—

Substitute Part Grouping Explanation

Substitution of the MR851 is determined by strict equivalence in the following electrical and mechanical parameters:

Critical Parameters for Substitution:

Voltage - DC Reverse (Vr) (Max): 100 V
Current - Average Rectified (Io): 3 A
Mounting Type: Through Hole
Package compatibility: DO-201AA, DO-27, or DO-201AD (axial configurations)

Secondary Parameters Affecting Compatibility:

Voltage - Forward (Vf) (Max) @ If: Must not exceed application requirements
Speed classification: Fast Recovery or Standard Recovery acceptable
Reverse Recovery Time (trr): Lower values indicate faster switching
Current - Reverse Leakage @ Vr: Lower values indicate better performance
Operating Temperature Range: Must encompass application requirements

Substitute parts are grouped into two categories:

Direct Equivalent (Same Manufacturer): MR851G by onsemi maintains identical electrical specifications and package format to the obsolete MR851, with active product status and RoHS3 compliance.

Functional Equivalents (Alternative Manufacturers): Parts meeting or exceeding the 100 V / 3 A electrical specification with compatible through-hole axial packaging. These include 1N5401G, EGP30B, 1N5401-G, 1N5401GP-AP, BYT56B-TAP, BYT56B-TR, FR302GP-AP, GI501-E3/54, and GI501-E3/73.

Parameter Comparison

Part Number	Manufacturer	Vr (Max) [V]	Io [A]	Vf (Max) @ If [V]	Speed	trr [ns]	Ir @ Vr [µA]	Package	Temp Range [°C]	Product Status	RoHS
MR851	onsemi	100	3	1.25 @ 3 A	Fast Recovery ≤ 500ns	300	10 @ 100 V	DO-201AA, DO-27, Axial	-65 to 125	Obsolete	Non-compliant
MR851G	onsemi	100	3	1.25 @ 3 A	Fast Recovery ≤ 500ns	300	10 @ 100 V	DO-201AA, DO-27, Axial	-65 to 125	Active	ROHS3 Compliant
1N5401G	Good-Ark Semiconductor	100	3	1.1 @ 3 A	Standard Recovery > 500ns	—	5 @ 100 V	DO-201AD, Axial	-55 to 150	Active	ROHS3 Compliant
EGP30B	Fairchild Semiconductor	100	3	0.95 @ 3 A	Fast Recovery ≤ 500ns	50	5 @ 100 V	DO-201AD, Axial	-65 to 150	Active	ROHS3 Compliant
1N5401-G	Comchip Technology	100	3	0.95 @ 3 A	Standard Recovery > 500ns	—	5 @ 100 V	DO-201AD, Axial	-65 to 125	Active	ROHS3 Compliant
1N5401GP-AP	Micro Commercial Co	100	3	1.1 @ 3 A	Standard Recovery > 500ns	—	5 @ 100 V	DO-201AD, Axial	-55 to 150	Active	ROHS3 Compliant
BYT56B-TAP	Vishay General Semiconductor - Diodes Division	100	3	1.4 @ 3 A	Fast Recovery ≤ 500ns	100	5 @ 100 V	SOD-64, Axial	-55 to 175	Active	ROHS3 Compliant
BYT56B-TR	Vishay General Semiconductor - Diodes Division	100	3	1.4 @ 3 A	Fast Recovery ≤ 500ns	100	5 @ 100 V	SOD-64, Axial	-55 to 175	Active	ROHS3 Compliant
FR302GP-AP	Micro Commercial Co	100	3	1.3 @ 3 A	Fast Recovery ≤ 500ns	150	5 @ 100 V	DO-201AD, Axial	-55 to 150	Active	ROHS3 Compliant
GI501-E3/54	Vishay General Semiconductor - Diodes Division	100	3	1.1 @ 9.4 A	Standard Recovery > 500ns	2000	5 @ 100 V	DO-201AD, Axial	-50 to 150	Active	ROHS3 Compliant
GI501-E3/73	Vishay General Semiconductor - Diodes Division	100	3	1.1 @ 9.4 A	Standard Recovery > 500ns	2000	5 @ 100 V	DO-201AD, Axial	-50 to 150	Active	ROHS3 Compliant

Engineering Selection Recommendations

Primary Recommendation - Direct Equivalent:

MR851G (onsemi) is the direct replacement for the obsolete MR851. It maintains identical electrical specifications, package format, and performance characteristics while offering active product status and RoHS3 compliance. This part is suitable for all applications previously using MR851 without design modification.

Secondary Recommendations - Functional Equivalents:

Selection among functional equivalents depends on specific application requirements:

For Fast Recovery Applications (≤ 500ns):

EGP30B (Fairchild Semiconductor): Lowest forward voltage (0.95 V @ 3 A), fastest recovery time (50 ns), extended temperature range (-65 to 150°C)
FR302GP-AP (Micro Commercial Co): Fast recovery (150 ns), moderate forward voltage (1.3 V @ 3 A), extended temperature range (-55 to 150°C)
BYT56B-TAP / BYT56B-TR (Vishay): Avalanche technology, fastest recovery (100 ns), extended temperature range (-55 to 175°C), higher forward voltage (1.4 V @ 3 A)

For Standard Recovery Applications (> 500ns):

1N5401G (Good-Ark Semiconductor): Low forward voltage (1.1 V @ 3 A), extended temperature range (-55 to 150°C)
1N5401-G (Comchip Technology): Low forward voltage (0.95 V @ 3 A), standard temperature range (-65 to 125°C)
1N5401GP-AP (Micro Commercial Co): Moderate forward voltage (1.1 V @ 3 A), extended temperature range (-55 to 150°C)
GI501-E3/54 / GI501-E3/73 (Vishay): Low forward voltage (1.1 V @ 9.4 A), extended temperature range (-50 to 150°C)

Compliance Considerations:

All substitute parts listed are RoHS3 compliant and REACH unaffected. The MR851 is RoHS non-compliant. Selection of RoHS3-compliant substitutes is required for new designs and applications subject to RoHS regulations.

Package Compatibility:

The MR851 uses DO-201AA and DO-27 axial packages. Most substitute parts use DO-201AD axial packages, which are mechanically and electrically compatible with DO-27 specifications. BYT56B variants use SOD-64 axial packages, also compatible with standard axial through-hole PCB layouts.

Frequently Asked Questions (FAQ)

Q: Can MR851G be used as a direct replacement for MR851 without any circuit modifications?

A: Yes. MR851G maintains identical electrical specifications (100 V, 3 A, 1.25 V forward voltage @ 3 A, 300 ns recovery time) and package format. No circuit modifications are required. The primary difference is active product status and RoHS3 compliance.

Q: What is the difference between DO-201AA, DO-27, and DO-201AD packages?

A: DO-201AA and DO-27 are equivalent axial package designations used by onsemi. DO-201AD is the industry-standard axial package designation used by other manufacturers. All three are mechanically and electrically compatible for through-hole PCB mounting. Pin spacing and lead diameter are equivalent.

Q: Why do some substitute parts have different forward voltage specifications?

A: Forward voltage varies based on semiconductor material quality, doping profile, and manufacturing process. EGP30B (0.95 V) and 1N5401-G (0.95 V) use optimized processes for lower forward voltage, reducing power dissipation. MR851 (1.25 V) and BYT56B (1.4 V) have higher forward voltages. Selection depends on thermal budget and efficiency requirements.

Q: What is the significance of recovery time (trr) differences?

A: Recovery time affects switching speed and reverse-bias transient response. Fast recovery diodes (≤ 500ns) are suitable for high-frequency switching applications and reduce EMI. Standard recovery diodes (> 500ns) are adequate for low-frequency rectification. MR851 specifies 300 ns (fast recovery). EGP30B (50 ns) and BYT56B (100 ns) offer superior high-frequency performance.

Q: Are BYT56B-TAP and BYT56B-TR interchangeable?

A: BYT56B-TAP (Tape & Box packaging) and BYT56B-TR (Tape & Reel packaging) are electrically and mechanically identical. The difference is packaging format for automated assembly. TAP is suitable for manual or small-batch assembly; TR is optimized for high-volume automated pick-and-place equipment.

Q: Can I use a substitute part with a lower reverse leakage current (5 µA vs. 10 µA)?

A: Yes. Lower reverse leakage current is a performance improvement. Parts with 5 µA leakage (1N5401G, EGP30B, 1N5401-G, etc.) will perform identically or better than MR851 (10 µA) in all applications. This reduces standby power consumption and improves circuit reliability.

Q: What is the difference between Standard and Avalanche technology diodes?

A: Standard diodes (1N5401, GI501, EGP30B) use conventional PN junction design. Avalanche diodes (BYT56B) are designed to operate safely in reverse-bias avalanche breakdown conditions, providing additional overvoltage protection. For general-purpose rectification at rated voltage, both technologies are equivalent. Avalanche diodes offer additional safety margin for transient overvoltage events.

Q: Which substitute part should I select for a new design?

A: For new designs, MR851G (onsemi) is the recommended choice as the direct equivalent with active product status. If extended temperature range is required, EGP30B (-65 to 150°C) or BYT56B variants (-55 to 175°C) are suitable. All recommended parts are RoHS3 compliant and have confirmed inventory availability.

Q: Are there any thermal considerations when selecting a substitute?

A: Forward voltage directly affects power dissipation (P = Vf × I). Lower forward voltage reduces heat generation. EGP30B (0.95 V) dissipates less heat than MR851 (1.25 V) at 3 A. Operating temperature range also varies: EGP30B and BYT56B support higher junction temperatures (150-175°C) compared to MR851 (125°C), allowing operation in higher ambient temperature environments.

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