BZX55C12 Equivalent & Substitute Parts

Part Overview

The BZX55C12 is a 12 V, 500 mW Zener diode manufactured by onsemi in DO-35 (DO-204AH) axial through-hole package. This component is classified as obsolete, though 6,265 units remain in stock. The BZX55C12 functions as a voltage regulator and protective element in electronic circuits requiring precise voltage reference or transient suppression at 12 V nominal.

Due to its obsolete status, equivalent and substitute parts from active manufacturers are necessary for new designs, long-term availability assurance, and compliance with current regulatory standards including RoHS3 and REACH requirements.

Key Parameters

Parameter	Value	Unit
Voltage - Zener (Nom)	12	V
Tolerance	±5	%
Power - Max	500	mW
Impedance (Max)	20	Ohms
Current - Reverse Leakage @ Vr	100	nA @ 9 V
Voltage - Forward (Vf) (Max) @ If	1.3	V @ 100 mA
Operating Temperature Range	-65 to 200	°C
Mounting Type	Through Hole	—
Package / Case	DO-204AH, DO-35, Axial	—

Substitute Part Grouping Explanation

Substitution of the BZX55C12 is determined by strict equivalence across the following critical parameters:

Primary Substitution Criteria:

Voltage - Zener (Nom): 12 V (exact match required)
Tolerance: ±5% (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 Compatibility Parameters:

Impedance (Max): 20–30 Ohms (acceptable range for functional equivalence)
Current - Reverse Leakage @ Vr: 100 nA or lower (acceptable range)
Voltage - Forward (Vf) (Max) @ If: 1.3–1.5 V (acceptable range)
Operating Temperature Range: -65°C minimum and 175–200°C maximum (acceptable range)

Parts are classified as Direct Substitutes when all primary criteria and most secondary criteria match. Parts are classified as Similar when one or more secondary parameters deviate (such as reduced power rating or different package variant) but maintain functional compatibility within defined limits.

Parameter Comparison

Part Number	Manufacturer	Vz (V)	Tolerance (%)	Power (mW)	Zzt (Ohms)	Ir @ Vr (nA)	Vf (V)	Temp Range (°C)	Package	Status
BZX55C12	onsemi	12	±5	500	20	100 @ 9 V	1.3 @ 100 mA	-65 to 200	DO-35	Obsolete
1N5242B	Microchip Technology	12	±5	500	30	1 µA @ 9.1 V	1.5 @ 200 mA	-65 to 175	DO-35	Active
BZX79C12	Taiwan Semiconductor Corporation	12	±5	500	25	100 @ 8 V	1.5 @ 100 mA	-65 to 175	DO-35	Active
BZX79C12-T50A	onsemi	12	±5	500	25	100 @ 8 V	1.5 @ 100 mA	-65 to 200	DO-35	Active
1N759A TR PBFREE	Central Semiconductor Corp	12	±5	500	30	100 @ 1 V	1.5 @ 200 mA	-65 to 200	DO-35	Active
BZX55C12-TR	Vishay General Semiconductor - Diodes Division	12	±5	500	20	100 @ 9.1 V	1.5 @ 200 mA	—	DO-35	Active
1N4883	Microchip Technology	12	±5	3000	5	10 µA @ 9.1 V	—	-65 to 175	Axial	Active
BZX79-C12,113	Nexperia USA Inc.	12	±5	400	25	100 @ 8 V	0.9 @ 10 mA	-65 to 200	ALF2	Active
BZX79-C12,133	Nexperia USA Inc.	12	±5	400	25	100 @ 8 V	0.9 @ 10 mA	-65 to 200	ALF2	Active
BZX79-C12,143	Nexperia USA Inc.	12	±5	400	25	100 @ 8 V	0.9 @ 10 mA	-65 to 200	ALF2	Active

Engineering Selection Recommendations

Direct Substitutes (Full Equivalence):

The following parts are direct substitutes for the BZX55C12 and maintain complete functional and mechanical compatibility:

BZX79C12-T50A (onsemi): Active product with identical 12 V, 500 mW specifications, DO-35 package, and extended operating temperature to 200°C. RoHS3 compliant. Recommended for designs requiring onsemi sourcing continuity.
1N759A TR PBFREE (Central Semiconductor Corp): Active product with 12 V, 500 mW specifications, DO-35 package, and full -65°C to 200°C operating range. RoHS3 compliant and lead-free. Suitable for applications with lead-free requirements.
BZX55C12-TR (Vishay General Semiconductor - Diodes Division): Active product maintaining the original BZX55 series designation with 12 V, 500 mW, DO-35 package. Includes AEC-Q101 automotive qualification. RoHS3 compliant. Recommended for automotive and high-reliability applications.

Functional Substitutes (Minor Parameter Variance):

The following parts provide functional equivalence with acceptable parameter deviations:

BZX79C12 (Taiwan Semiconductor Corporation): Active product with 12 V, 500 mW, DO-35 package. Impedance of 25 Ohms (vs. 20 Ohms nominal) and operating temperature limited to 175°C. RoHS3 compliant. Suitable for general-purpose applications not requiring extended temperature operation.
1N5242B (Microchip Technology): Active product with 12 V, 500 mW, DO-35 package. Impedance of 30 Ohms and operating temperature limited to 175°C. RoHS non-compliant. Acceptable for legacy designs where RoHS compliance is not mandated.

Similar Parts (Reduced Power Rating):

The following parts maintain 12 V regulation but with reduced power dissipation capability:

BZX79-C12,113, BZX79-C12,133, BZX79-C12,143 (Nexperia USA Inc.): Active products with 12 V, 400 mW (vs. 500 mW), ALF2 package variant. RoHS3 compliant and -65°C to 200°C operating range. Suitable only for applications with power dissipation requirements ≤400 mW.

Higher Power Alternative (Different Package):

1N4883 (Microchip Technology): Active product with 12 V, 3 W power rating in axial package. Significantly higher power capability but different mechanical form factor. Suitable only for applications requiring higher power dissipation and compatible with axial lead mounting.

Frequently Asked Questions (FAQ)

Q: Can I use BZX79C12 as a direct replacement for BZX55C12?

A: BZX79C12 is functionally compatible with acceptable parameter variance. The impedance increases from 20 Ohms to 25 Ohms, and the maximum operating temperature reduces from 200°C to 175°C. For applications operating below 175°C with impedance tolerance, this substitution is valid. For extended temperature applications, BZX79C12-T50A or 1N759A TR PBFREE are preferred.

Q: What is the difference between BZX55C12-TR and BZX79C12-T50A?

A: Both are active 12 V, 500 mW, DO-35 Zener diodes. BZX55C12-TR maintains the original BZX55 series designation and includes AEC-Q101 automotive qualification, making it suitable for automotive applications. BZX79C12-T50A is from the BZX79 series and is suitable for general industrial applications. Both support -65°C to 200°C operation and are RoHS3 compliant.

Q: Why are BZX79-C12,113 and similar parts listed as similar rather than direct substitutes?

A: These parts have a reduced power rating of 400 mW compared to the 500 mW specification of BZX55C12. They are suitable only for applications where power dissipation does not exceed 400 mW. The ALF2 package is also a variant form factor. Use these parts only when power requirements are confirmed to be within the 400 mW limit.

Q: Is 1N5242B suitable for my application?

A: 1N5242B is functionally compatible with acceptable parameter variance. However, it is RoHS non-compliant, which may restrict its use in applications subject to RoHS regulations. The operating temperature is limited to 175°C. For new designs, RoHS3-compliant alternatives such as BZX79C12, BZX79C12-T50A, or 1N759A TR PBFREE are recommended.

Q: Can I use 1N4883 as a substitute?

A: 1N4883 is not a direct substitute. While it maintains the 12 V nominal voltage, it has a significantly higher power rating of 3 W and uses an axial package instead of DO-35. Use 1N4883 only in applications requiring higher power dissipation and compatible with axial lead mounting.

Q: What does "RoHS3 Compliant" mean for my selection?

A: RoHS3 compliance indicates the part meets the Restriction of Hazardous Substances Directive, restricting lead and other hazardous materials. For applications subject to RoHS regulations (including consumer electronics, automotive, and industrial equipment in regulated markets), select only RoHS3-compliant alternatives. BZX79C12-T50A, 1N759A TR PBFREE, BZX55C12-TR, and Nexperia parts are RoHS3 compliant.

Q: What is the significance of the DO-35 package specification?

A: DO-35 (DO-204AH) is the axial through-hole package form factor of the BZX55C12. All direct and functional substitutes maintain this package specification, ensuring mechanical and electrical compatibility with existing PCB designs and mounting hardware. Parts with different packages (such as ALF2 or axial variants) require PCB layout modifications.

Q: Are there any temperature-related limitations I should consider?

A: The BZX55C12 operates from -65°C to 200°C. Most active substitutes support this full range, except BZX79C12 and 1N5242B, which are limited to 175°C maximum. For applications requiring operation above 175°C, select BZX79C12-T50A, 1N759A TR PBFREE, BZX55C12-TR, or Nexperia parts.

Q: What does "Impedance (Max)" mean in the context of Zener diode selection?

A: Impedance (Zzt) represents the dynamic impedance of the Zener diode at the nominal Zener voltage. Lower impedance values indicate better voltage regulation characteristics and lower output impedance. The BZX55C12 specifies 20 Ohms maximum. Substitutes with impedance up to 30 Ohms are functionally acceptable for most applications, though lower impedance provides superior regulation performance.

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