BZX55C56 Equivalent & Substitute Parts

Part Overview

The BZX55C56 is a through-hole zener diode rated at 56 V nominal with 500 mW maximum power dissipation in a DO-35 package. Manufactured by onsemi, this component is classified as obsolete. Due to its obsolete status and limited current inventory availability, identifying equivalent substitute parts with compatible electrical and mechanical specifications is necessary for ongoing design support and production continuity.

Key Parameters

Parameter	Value
Voltage - Zener (Nom)	56 V
Power - Max	500 mW
Tolerance	±7%
Impedance (Max)	135 Ohms
Mounting Type	Through Hole
Package / Case	DO-35
Operating Temperature Range	-65°C ~ 200°C
Product Status	Obsolete

Substitute Part Grouping Explanation

Substitute parts for the BZX55C56 are selected based on the following critical parameters that determine functional compatibility:

Primary Matching Criteria:

Voltage - Zener (Nom): 56 V (exact match required)
Mounting Type: Through Hole (mechanical compatibility)
Package Category: Axial configuration (physical form factor)

Secondary Compatibility Factors:

Power - Max: Equal to or greater than 500 mW
Tolerance: ±7% or tighter
Operating Temperature Range: Must encompass or exceed -65°C to 200°C
Impedance (Max): Lower values indicate improved regulation characteristics

Substitute parts may exceed the original specifications in power rating, impedance performance, and temperature range. These enhancements provide design flexibility without compromising circuit function.

Parameter Comparison

Parameter	BZX55C56 (Main)	1N4758A (Substitute)	1N5087 (Substitute)
Manufacturer	onsemi	SMC Diode Solutions	Microchip Technology
Voltage - Zener (Nom)	56 V	56 V	56 V
Tolerance	±7%	±5%	±5%
Power - Max	500 mW	1 W	3 W
Impedance (Max)	135 Ohms	110 Ohms	70 Ohms
Current - Reverse Leakage @ Vr	100 nA @ 42 V	5 µA @ 42.6 V	1 µA @ 42.6 V
Voltage - Forward (Vf) (Max) @ If	1.3 V @ 100 mA	1.2 V @ 200 mA	Not specified
Operating Temperature Range	-65°C ~ 200°C	Up to 200°C	-65°C ~ 175°C
Mounting Type	Through Hole	Through Hole	Through Hole
Package / Case	DO-35	DO-41	Axial
Product Status	Obsolete	Obsolete	Active
REACH Status	REACH Unaffected	REACH Unaffected	REACH Unaffected
ECCN	EAR99	EAR99	EAR99

Engineering Selection Recommendations

1N4758A Selection Criteria: The 1N4758A provides a direct voltage match at 56 V with improved tolerance (±5% versus ±7%) and doubled power rating (1 W versus 500 mW). The DO-41 package is physically larger than DO-35, requiring PCB layout verification. This part is obsolete but maintains REACH compliance and EAR99 classification. Impedance improvement (110 Ohms versus 135 Ohms) enhances voltage regulation performance.

1N5087 Selection Criteria: The 1N5087 is the preferred substitute due to active product status, ensuring long-term availability and supply chain stability. It delivers 56 V nominal voltage with ±5% tolerance and significantly improved power handling (3 W versus 500 mW). The impedance specification (70 Ohms) provides superior regulation characteristics. Operating temperature range extends to 175°C, meeting the lower bound of the original specification. RoHS3 compliance adds environmental qualification. The axial package form factor is compatible with through-hole mounting applications.

Compliance and Regulatory Alignment: All substitute parts maintain REACH Unaffected status and EAR99 export classification, ensuring regulatory continuity with the original BZX55C56.

Frequently Asked Questions (FAQ)

Q: Can the 1N4758A directly replace the BZX55C56 in all applications?

A: The 1N4758A matches the 56 V zener voltage and exceeds power specifications. However, the DO-41 package is physically larger than DO-35. PCB layout and mechanical clearance must be verified before substitution. Both parts are obsolete.

Q: Why is the 1N5087 recommended as the primary substitute?

A: The 1N5087 is the only active product among the substitutes, providing assured long-term availability. It meets all electrical requirements with superior performance margins (3 W power, 70 Ohms impedance, ±5% tolerance) and includes RoHS3 compliance certification.

Q: Are there package compatibility concerns between DO-35 and DO-41?

A: DO-35 and DO-41 are both axial through-hole packages with different physical dimensions. DO-41 is larger. Footprint spacing and lead hole diameter must be verified against PCB design specifications. Both accommodate standard 0.040-inch lead diameter.

Q: What is the impact of impedance differences on circuit performance?

A: Lower impedance values (1N5087 at 70 Ohms, 1N4758A at 110 Ohms versus BZX55C56 at 135 Ohms) improve voltage regulation stability and reduce output impedance variation across the operating current range. This enhancement is beneficial in most applications.

Q: Does the 1N5087 operating temperature range of -65°C to 175°C create limitations?

A: The 1N5087 maximum temperature is 175°C, which is 25°C below the BZX55C56 specification of 200°C. Applications requiring sustained operation above 175°C require thermal analysis to confirm the 1N5087 remains within safe operating limits.

Q: Are all substitute parts REACH and export compliant?

A: Yes. All three parts (BZX55C56, 1N4758A, and 1N5087) maintain REACH Unaffected status and EAR99 export classification, ensuring regulatory continuity.

Q: What is the significance of the ±5% tolerance improvement in substitute parts?

A: The 1N4758A and 1N5087 offer ±5% tolerance versus the BZX55C56 at ±7%. Tighter tolerance reduces zener voltage variation across production batches, improving circuit performance consistency and reducing design margin requirements.

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