BZX55A18-TAP Equivalent & Substitute Parts

Part Overview

The BZX55A18-TAP is a Zener diode rated at 18 V, 500 mW, manufactured by Vishay General Semiconductor - Diodes Division. This component is classified as obsolete, though 990 pieces remain in stock. The BZX55A18-TAP features AEC-Q101 automotive qualification and ROHS3 compliance, designed for through-hole mounting in DO-204AH (DO-35) axial package configuration.

Substitute parts are necessary due to the obsolete product status of the BZX55A18-TAP. Active alternatives maintain the core electrical specifications while offering improved availability and, in some cases, enhanced operational characteristics.

Key Parameters

Parameter	BZX55A18-TAP
Voltage - Zener (Nom)	18 V
Tolerance	±1%
Power - Max	500 mW
Impedance (Max)	50 Ohms
Current - Reverse Leakage @ Vr	100 nA @ 13 V
Voltage - Forward (Vf) (Max) @ If	1.5 V @ 200 mA
Operating Temperature	175°C
Grade	Automotive
Qualification	AEC-Q101
Mounting Type	Through Hole
Package / Case	DO-204AH, DO-35, Axial
RoHS Status	ROHS3 Compliant
Product Status	Obsolete

Substitute Part Grouping Explanation

Substitution of the BZX55A18-TAP is determined by the following critical parameters:

Primary Matching Criteria:

Zener voltage: 18 V nominal
Power dissipation: 500 mW maximum
Package type: DO-204AH (DO-35) axial through-hole
Mounting configuration: Through-hole

Secondary Compatibility Factors:

Operating temperature range
Tolerance specification (±1% to ±5%)
Impedance characteristics
Forward voltage characteristics
Reverse leakage current specifications
RoHS and regulatory compliance status

Substitute parts are grouped into two categories: direct equivalents with tighter tolerance specifications and functional alternatives with relaxed tolerance but equivalent electrical performance under nominal operating conditions.

Parameter Comparison

Part Number	Manufacturer	Vz (Nom)	Tolerance	Power (Max)	Zzt (Max)	Vf (Max) @ If	Operating Temp	Product Status	RoHS Status
BZX55A18-TAP	Vishay	18 V	±1%	500 mW	50 Ohms	1.5 V @ 200 mA	175°C	Obsolete	ROHS3
BZX55B18-TAP	Vishay	18 V	±2%	500 mW	50 Ohms	1.5 V @ 200 mA	-65°C ~ 175°C	Active	ROHS3
1N3524A	Microchip Technology	18 V	±5%	500 mW	18 Ohms	1.1 V @ 200 mA	-65°C ~ 175°C	Active	Non-compliant
1N5248B	Microchip Technology	18 V	±5%	500 mW	21 Ohms	1.5 V @ 200 mA	-65°C ~ 175°C	Active	Non-compliant
1N5248BDO35	Microsemi Corporation	18 V	±5%	500 mW	21 Ohms	1.5 V @ 200 mA	-65°C ~ 175°C	Active	Non-compliant
1N5248BTR	Fairchild Semiconductor	18 V	±5%	500 mW	21 Ohms	1.2 V @ 200 mA	-65°C ~ 200°C	Active	Not specified
1N5538B	Microchip Technology	18 V	±5%	500 mW	105 Ohms	1.1 V @ 200 mA	-65°C ~ 175°C	Active	Non-compliant
1N5742B	Microchip Technology	18 V	±5%	500 mW	45 Ohms	900 mV @ 10 mA	-65°C ~ 175°C	Active	Non-compliant

Engineering Selection Recommendations

Primary Substitute: BZX55B18-TAP

The BZX55B18-TAP is the recommended primary substitute. Manufactured by the same supplier (Vishay General Semiconductor - Diodes Division), this part maintains identical electrical specifications with the exception of tolerance (±2% versus ±1%) and expanded operating temperature range (-65°C to 175°C). The BZX55B18-TAP carries active product status with 34,466 units in stock and maintains ROHS3 compliance. The tolerance relaxation from ±1% to ±2% is acceptable for most applications requiring 18 V Zener regulation.

Secondary Substitutes: 1N5248B, 1N5248BDO35, 1N5248BTR

These parts provide functional equivalence with 18 V nominal Zener voltage and 500 mW power rating. All three maintain identical impedance characteristics (21 Ohms) and forward voltage specifications (1.5 V @ 200 mA). The 1N5248BTR variant offers the widest operating temperature range (-65°C to 200°C) and lowest forward voltage at rated current (1.2 V @ 200 mA). These alternatives carry active product status with substantial inventory availability. However, these parts are RoHS non-compliant, which may restrict use in applications requiring regulatory compliance.

Alternative Substitutes: 1N3524A, 1N5538B, 1N5742B

These parts satisfy the core electrical requirements of 18 V nominal Zener voltage and 500 mW power dissipation. Impedance characteristics vary significantly (18 Ohms, 105 Ohms, and 45 Ohms respectively), which may affect circuit performance in applications sensitive to dynamic impedance. All three carry active product status but are RoHS non-compliant. Selection of these alternatives requires verification that impedance variations do not compromise circuit function.

Frequently Asked Questions (FAQ)

Q: Can BZX55B18-TAP directly replace BZX55A18-TAP in all applications?

A: The BZX55B18-TAP is a direct functional replacement for the BZX55A18-TAP. The tolerance specification changes from ±1% to ±2%, which is acceptable in most voltage regulation applications. The expanded operating temperature range (-65°C to 175°C) provides additional operational margin. Both parts share identical impedance (50 Ohms) and forward voltage characteristics (1.5 V @ 200 mA).

Q: What is the significance of impedance (Zzt) differences among substitute parts?

A: Impedance (Zzt) affects the dynamic response of the Zener diode to transient voltage changes. Lower impedance values (18 Ohms for 1N3524A) provide faster voltage regulation response, while higher impedance values (105 Ohms for 1N5538B) result in slower response. Applications requiring precise transient suppression should verify impedance compatibility with circuit requirements.

Q: Are all substitute parts suitable for automotive applications?

A: The BZX55A18-TAP and BZX55B18-TAP carry AEC-Q101 automotive qualification. The substitute parts (1N3524A, 1N5248B, 1N5248BDO35, 1N5248BTR, 1N5538B, 1N5742B) do not specify automotive qualification in the provided data. Applications requiring automotive-grade components should prioritize BZX55B18-TAP.

Q: What is the impact of RoHS compliance status on part selection?

A: The BZX55A18-TAP and BZX55B18-TAP are ROHS3 compliant. The alternative substitutes (1N3524A, 1N5248B, 1N5248BDO35, 1N5538B, 1N5742B) are RoHS non-compliant. Applications subject to RoHS regulations or customer requirements for lead-free components must use BZX55B18-TAP or verify regulatory exemptions for non-compliant alternatives.

Q: Can forward voltage differences affect circuit performance?

A: Forward voltage specifications vary among substitutes. The BZX55A18-TAP specifies 1.5 V @ 200 mA. Alternatives range from 900 mV @ 10 mA (1N5742B) to 1.5 V @ 200 mA (1N5248B, 1N5248BDO35). Forward voltage differences are relevant only in reverse-biased Zener operation; in forward-biased applications, these variations may affect circuit behavior and require verification.

Q: Is the operating temperature range expansion in BZX55B18-TAP significant?

A: The BZX55A18-TAP specifies a maximum operating temperature of 175°C without a minimum specification. The BZX55B18-TAP specifies -65°C to 175°C. This expanded range provides operational margin for low-temperature environments and is beneficial for applications subject to wide temperature variation. The expanded range does not restrict use in applications limited to the original temperature specification.

Q: What inventory considerations apply to substitute part selection?

A: The BZX55A18-TAP has 990 units in stock (obsolete status). The BZX55B18-TAP has 34,466 units available (active status), providing superior long-term supply assurance. Alternative substitutes have lower inventory levels (812 to 62,638 units depending on part number). For applications requiring sustained component availability, BZX55B18-TAP is the preferred choice.

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