TZX18A-TR Equivalent & Substitute Parts

Part Overview

The TZX18A-TR is an 18 V, 500 mW Zener diode manufactured by Vishay General Semiconductor - Diodes Division in the DO-35 (DO-204AH) axial through-hole package. This component is classified as an active product with AEC-Q101 automotive qualification and ROHS3 compliance. Substitute parts are identified when equivalent electrical performance, mechanical compatibility, and operational parameters align with the original specification, enabling direct replacement in circuit applications without design modification.

Key Parameters

Parameter	Value	Unit
Voltage - Zener (Nominal)	18	V
Power - Maximum	500	mW
Impedance (Maximum)	55	Ohms
Current - Reverse Leakage @ Vr	1	µA @ 13 V
Voltage - Forward (Maximum) @ If	1.5	V @ 200 mA
Operating Temperature Range	-65 to 175	°C
Package / Case	DO-204AH (DO-35)	Axial
Mounting Type	Through Hole	-
RoHS Status	ROHS3 Compliant	-
Grade	Automotive	-

Substitute Part Grouping Explanation

Substitution of the TZX18A-TR is determined by the following critical parameters:

Primary Substitution Criteria:

Zener voltage nominal value: 18 V (tolerance range acceptable within application circuit design margins)
Power dissipation rating: 500 mW minimum
Package compatibility: DO-35 (DO-204AH) axial through-hole configuration
Operating temperature range: Minimum -65°C to 175°C overlap required
Forward voltage and reverse leakage characteristics within acceptable circuit operating limits

Secondary Compatibility Factors:

Impedance (Zzt) maximum: Affects voltage regulation stability; lower impedance provides improved regulation
Reverse leakage current: Lower leakage reduces standby power consumption
Voltage tolerance: Tighter tolerance (±2% to ±5%) improves voltage regulation accuracy
Compliance certifications: RoHS and REACH status for regulatory requirements

The three substitute parts identified (1N5248B, 1N5248BTR, and NZX18A,133) meet the primary substitution criteria with variations in secondary parameters that do not prevent functional equivalence in standard Zener diode applications.

Parameter Comparison

Parameter	TZX18A-TR (Main)	1N5248B	1N5248BTR	NZX18A,133
Manufacturer	Vishay General Semiconductor	Microchip Technology	Fairchild Semiconductor	Nexperia USA Inc.
Voltage - Zener (Nom)	18 V	18 V	18 V	17.3 V
Tolerance	-	±5%	±5%	±2%
Power - Max	500 mW	500 mW	500 mW	500 mW
Impedance (Max)	55 Ohms	21 Ohms	21 Ohms	55 Ohms
Current - Reverse Leakage @ Vr	1 µA @ 13 V	100 nA @ 14 V	100 nA @ 14 V	50 nA @ 12.6 V
Voltage - Forward (Max) @ If	1.5 V @ 200 mA	1.5 V @ 200 mA	1.2 V @ 200 mA	1.5 V @ 200 mA
Operating Temperature	-65 to 175°C	-65 to 175°C	-65 to 200°C	-55 to 175°C
Package / Case	DO-204AH (DO-35)	DO-204AH (DO-35)	DO-204AH (DO-35)	DO-204AH (DO-35)
Mounting Type	Through Hole	Through Hole	Through Hole	Through Hole
RoHS Status	ROHS3 Compliant	RoHS Non-Compliant	Not Specified	ROHS3 Compliant

Engineering Selection Recommendations

1N5248B (Microchip Technology)

This substitute provides equivalent 18 V, 500 mW performance with improved impedance characteristics (21 Ohms vs. 55 Ohms) and significantly lower reverse leakage current (100 nA vs. 1 µA). The ±5% voltage tolerance is acceptable for general Zener applications. Operating temperature range matches the original specification. RoHS non-compliance status requires verification against end-application regulatory requirements. This part is suitable for applications where improved voltage regulation and reduced standby leakage are beneficial.

1N5248BTR (Fairchild Semiconductor)

This substitute offers identical electrical performance to the 1N5248B with an extended operating temperature range (-65°C to 200°C), providing additional thermal margin. Forward voltage is reduced to 1.2 V at 200 mA, indicating superior forward conduction characteristics. Impedance and reverse leakage parameters match the 1N5248B. RoHS compliance status is not specified in the provided data. This part is suitable for applications requiring extended temperature operation.

NZX18A,133 (Nexperia USA Inc.)

This substitute operates at a nominal Zener voltage of 17.3 V with ±2% tolerance, representing a 0.7 V reduction from the 18 V specification. Impedance characteristics (55 Ohms) match the original TZX18A-TR. Reverse leakage current is superior at 50 nA. Operating temperature range is -55°C to 175°C, with the lower limit at -55°C (10°C higher than the original). ROHS3 compliance is maintained. This part is suitable for applications where the 17.3 V nominal voltage is acceptable within circuit design margins and where improved leakage performance is required.

Compliance Considerations

The TZX18A-TR maintains ROHS3 compliance and AEC-Q101 automotive qualification. The 1N5248B is RoHS non-compliant, requiring assessment against application requirements. The NZX18A,133 maintains ROHS3 compliance, providing direct regulatory equivalence. All substitute parts are classified as active products with unlimited moisture sensitivity (MSL 1).

Frequently Asked Questions (FAQ)

Q: Can the 1N5248B directly replace the TZX18A-TR in automotive applications?

A: The 1N5248B provides electrical equivalence at 18 V, 500 mW with improved impedance and leakage characteristics. However, RoHS non-compliance status must be evaluated against specific automotive qualification requirements. The original TZX18A-TR carries AEC-Q101 qualification; the 1N5248B qualification status is not specified in the provided data.

Q: What is the significance of the impedance difference between TZX18A-TR (55 Ohms) and 1N5248B (21 Ohms)?

A: Lower impedance (21 Ohms) in the 1N5248B provides improved voltage regulation stability and faster transient response. This is a performance enhancement for Zener regulation applications. The higher impedance (55 Ohms) of the TZX18A-TR and NZX18A,133 is acceptable for standard voltage reference applications.

Q: Is the NZX18A,133 at 17.3 V suitable as a substitute for the 18 V TZX18A-TR?

A: The 17.3 V nominal voltage represents a 3.9% reduction from 18 V. Substitution is determined by circuit design margins and voltage tolerance requirements. Applications requiring precise 18 V regulation should use 1N5248B or 1N5248BTR. The NZX18A,133 is suitable for applications where 17.3 V ±2% meets the design specification.

Q: What is the impact of reverse leakage current differences on circuit performance?

A: The TZX18A-TR specifies 1 µA reverse leakage at 13 V. Substitute parts offer lower leakage: 1N5248B and 1N5248BTR at 100 nA, and NZX18A,133 at 50 nA. Lower leakage reduces standby power consumption and improves voltage regulation stability, particularly in high-impedance circuits.

Q: Are all substitute parts available in the same DO-35 package?

A: All substitute parts are packaged in DO-204AH (DO-35) axial through-hole configuration, providing direct mechanical compatibility with the TZX18A-TR. No PCB layout or mounting modifications are required.

Q: What is the operating temperature consideration for the 1N5248BTR?

A: The 1N5248BTR operates from -65°C to 200°C, extending 25°C above the TZX18A-TR specification (-65°C to 175°C). This provides additional thermal margin for applications operating at elevated temperatures. The NZX18A,133 lower operating limit is -55°C, which is 10°C higher than the original specification.

Q: How do voltage tolerances affect substitution decisions?

A: The TZX18A-TR tolerance is not specified. Substitute parts offer ±5% (1N5248B, 1N5248BTR) and ±2% (NZX18A,133). Tighter tolerance improves voltage regulation accuracy. Selection depends on circuit voltage regulation requirements and acceptable tolerance bands.

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