TZX18A-TAP Equivalent & Substitute Parts

Part Overview

The TZX18A-TAP is an 18 V, 500 mW Zener diode manufactured by Vishay General Semiconductor - Diodes Division in a through-hole DO-35 (DO-204AH) package. This component is classified as an active product with AEC-Q101 automotive qualification and ROHS3 compliance. Zener diodes of this specification are used in voltage regulation, overvoltage protection, and reference voltage applications across automotive, industrial, and consumer electronics circuits. Substitute parts become necessary due to inventory constraints, supply chain discontinuities, or design flexibility requirements while maintaining electrical and mechanical compatibility.

Key Parameters

Parameter	Value	Unit
Voltage - Zener (Nominal)	18	V
Power - Maximum	500	mW
Package / Case	DO-204AH, DO-35, Axial	—
Mounting Type	Through Hole	—
Operating Temperature Range	-65 to 175	°C
RoHS Status	ROHS3 Compliant	—

Substitute Part Grouping Explanation

Substitution of the TZX18A-TAP is determined by strict alignment of the following electrical and mechanical parameters:

Critical Matching Parameters:

Zener voltage: 18 V nominal
Power dissipation: 500 mW maximum
Package type: DO-35 (DO-204AH) through-hole axial configuration
Operating temperature range: minimum -65°C to 175°C

Secondary Compatibility Parameters:

Voltage tolerance (±5% acceptable for most applications)
Impedance characteristics (Zzt)
Reverse leakage current specifications
Forward voltage drop characteristics

All substitute parts listed maintain the core electrical specifications (18 V, 500 mW) and identical package geometry, ensuring direct mechanical and electrical interchangeability in circuit designs. Variations in impedance, leakage current, and forward voltage are within acceptable ranges for standard voltage regulation and protection applications.

Parameter Comparison

Parameter	TZX18A-TAP (Vishay)	1N5248B (Microchip)	1N5248B TR PBFREE (Central Semiconductor)	BZX79C18-T50A (Fairchild)
Manufacturer	Vishay General Semiconductor	Microchip Technology	Central Semiconductor Corp	Fairchild Semiconductor
Voltage - Zener (Nom)	18 V	18 V	18 V	18 V
Tolerance	—	±5%	±5%	±5%
Power - Max	500 mW	500 mW	500 mW	500 mW
Impedance (Max) (Zzt)	55 Ohms	21 Ohms	21 Ohms	45 Ohms
Current - Reverse Leakage @ Vr	1 µA @ 13 V	100 nA @ 14 V	100 nA @ 14 V	50 nA @ 12.6 V
Voltage - Forward (Vf) (Max) @ If	1.5 V @ 200 mA	1.5 V @ 200 mA	1.1 V @ 200 mA	1.5 V @ 100 mA
Operating Temperature	-65 to 175°C	-65 to 175°C (TJ)	-65 to 200°C	-65 to 200°C
Package / Case	DO-204AH, DO-35, Axial	DO-204AH, DO-35, Axial	DO-204AH, DO-35, Axial	DO-204AH, DO-35, Axial
Mounting Type	Through Hole	Through Hole	Through Hole	Through Hole
RoHS Status	ROHS3 Compliant	RoHS non-compliant	ROHS3 Compliant	Not specified
Product Status	Active	Active	Active	Active

Engineering Selection Recommendations

Primary Substitute: 1N5248B TR PBFREE (Central Semiconductor Corp)

The 1N5248B TR PBFREE is the optimal substitute for the TZX18A-TAP. Both components share ROHS3 compliance, identical 18 V / 500 mW electrical specifications, and DO-35 through-hole package geometry. The 1N5248B TR PBFREE extends the operating temperature range to 200°C and features lower forward voltage (1.1 V @ 200 mA) and reduced impedance (21 Ohms), providing superior performance characteristics. This part is suitable for applications requiring RoHS compliance and automotive-grade reliability.

Secondary Substitute: BZX79C18-T50A (Fairchild Semiconductor)

The BZX79C18-T50A maintains full electrical and mechanical compatibility with the TZX18A-TAP, offering 18 V / 500 mW specifications in the DO-35 package. This part provides an extended operating temperature range to 200°C and lower reverse leakage current (50 nA @ 12.6 V). RoHS compliance status is not specified; verification is required for applications with RoHS mandates.

Tertiary Substitute: 1N5248B (Microchip Technology)

The 1N5248B from Microchip Technology provides electrical equivalence with 18 V / 500 mW ratings and DO-35 package compatibility. This part is not RoHS compliant and is suitable only for applications without RoHS requirements. The operating temperature range matches the TZX18A-TAP at -65°C to 175°C.

All substitute parts are active products with established supply availability and are suitable for direct circuit replacement where package and electrical specifications align with design requirements.

Frequently Asked Questions (FAQ)

Q: Can the 1N5248B (Microchip) be used in place of the TZX18A-TAP in automotive applications?

A: The 1N5248B provides electrical equivalence (18 V, 500 mW) and identical package geometry. However, the TZX18A-TAP carries AEC-Q101 automotive qualification, while the 1N5248B does not specify this certification. For automotive applications requiring AEC-Q101 compliance, use the 1N5248B TR PBFREE or BZX79C18-T50A instead.

Q: What is the difference between the 1N5248B and 1N5248B TR PBFREE?

A: Both parts share identical electrical specifications (18 V, 500 mW, ±5% tolerance). The 1N5248B TR PBFREE is ROHS3 compliant with an extended operating temperature range (-65°C to 200°C) and lower forward voltage (1.1 V @ 200 mA). The standard 1N5248B is RoHS non-compliant. Select the TR PBFREE variant for RoHS-regulated applications.

Q: Are all substitute parts available in the same packaging format?

A: Yes. All substitute parts (1N5248B, 1N5248B TR PBFREE, and BZX79C18-T50A) are supplied in DO-35 (DO-204AH) through-hole axial packages, identical to the TZX18A-TAP. Direct mechanical substitution is possible without PCB redesign.

Q: How do impedance differences affect circuit performance?

A: The TZX18A-TAP has 55 Ohms maximum impedance, while the 1N5248B variants and BZX79C18-T50A have lower impedance (21 and 45 Ohms respectively). Lower impedance provides improved voltage regulation stability and faster transient response. For voltage reference and protection circuits, lower impedance is generally beneficial. For high-impedance applications, verify circuit performance requirements.

Q: Which substitute part has the lowest reverse leakage current?

A: The BZX79C18-T50A has the lowest reverse leakage current at 50 nA @ 12.6 V, followed by the 1N5248B variants at 100 nA @ 14 V. The TZX18A-TAP specifies 1 µA @ 13 V. Lower leakage current reduces standby power consumption in voltage reference applications.

Q: Is the extended temperature range of the 1N5248B TR PBFREE (-65°C to 200°C) necessary for standard applications?

A: The extended range to 200°C provides operational margin for high-temperature environments and thermal stress conditions. For applications operating within -65°C to 175°C, the standard TZX18A-TAP or 1N5248B specifications are sufficient. Extended range is beneficial for automotive underhood, industrial, and aerospace applications.

Q: Can I use these Zener diodes interchangeably in existing designs without circuit analysis?

A: All substitute parts maintain the critical 18 V / 500 mW specifications and DO-35 package compatibility. However, variations in impedance, leakage current, and forward voltage may affect circuit performance in precision voltage reference or high-frequency transient protection applications. Review circuit requirements for impedance sensitivity and leakage current specifications before final selection.

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