BZX84C3V9 Zener Diode Equivalent & Substitute Parts

Part Overview

The BZX84C3V9 is a surface-mount Zener diode manufactured by onsemi, rated at 3.9 V nominal Zener voltage with 350 mW maximum power dissipation in a SOT-23-3 package. This part is classified as obsolete, making equivalent and substitute parts necessary for ongoing design support and procurement. The BZX84C3V9 serves voltage regulation and protection applications requiring precise 3.9 V reference characteristics with ±5% tolerance in compact surface-mount form factor.

Key Parameters

Parameter	Value	Unit
Voltage - Zener (Nom)	3.9	V
Tolerance	±5%	—
Power - Max	350	mW
Impedance (Max)	90	Ohms
Current - Reverse Leakage @ Vr	5	µA @ 1 V
Voltage - Forward (Vf) (Max) @ If	900	mV @ 10 mA
Operating Temperature	-55 to 150	°C
Mounting Type	Surface Mount	—
Package / Case	SOT-23-3	—
Moisture Sensitivity Level	1 (Unlimited)	—

Substitute Part Grouping Explanation

Substitution of the BZX84C3V9 is determined by the following critical parameters:

Primary Substitution Criteria:

Zener voltage: 3.9 V nominal
Tolerance: ±5% or tighter
Package: SOT-23-3 (TO-236-3, SC-59)
Mounting type: Surface Mount
Operating temperature range: minimum -55°C to 150°C

Secondary Compatibility Factors:

Power dissipation: 225 mW minimum (lower than original 350 mW is acceptable for lower-power applications)
Impedance: 90 Ohms maximum
Forward voltage: 900 mV maximum @ 10 mA
Reverse leakage: 5 µA maximum @ 1 V

Substitute parts are grouped into three categories:

Direct Equivalents (onsemi BZX84C series): Parts maintaining identical electrical specifications with different packaging or product status transitions.
Automotive-Grade Alternatives (onsemi SZBZX84 and SZMMBZ5228 series): Parts with AEC-Q101 qualification, lower power ratings (225 mW), and enhanced temperature range (-65°C to 150°C).
Cross-Manufacturer Alternatives: Parts from Comchip Technology, Nexperia, NXP, and Vishay meeting core electrical parameters with varying tolerance and power specifications.

Parameter Comparison

Part Number	Manufacturer	Vz (V)	Tolerance	Power (mW)	Zzt (Ohms)	Vf @ 10mA (mV)	Temp Range (°C)	Status	Package
BZX84C3V9	onsemi	3.9	±5%	350	90	900	-55 to 150	Obsolete	SOT-23-3
BZX84C3V9LT1G	onsemi	3.9	±5%	225	90	900	-65 to 150	Active	SOT-23-3
SZBZX84C3V9ET1G	onsemi	3.9	±5%	225	90	900	-65 to 150	Active	SOT-23-3
SZBZX84C3V9ET3G	onsemi	3.9	±5%	225	90	900	-65 to 150	Active	SOT-23-3
SZBZX84C3V9LT1G	onsemi	3.9	±5%	225	90	900	-65 to 150	Active	SOT-23-3
SZMMBZ5228BLT1G	onsemi	3.9	±5%	225	23	900	-65 to 150	Active	SOT-23-3
CZRT55C3V9-G	Comchip Technology	3.9	±5%	350	90	900	-65 to 150	Active	SOT-23-3
BZX84-A3V9,215	Nexperia USA Inc.	3.9	±1%	250	90	900	-65 to 150	Active	SOT-23-3
BZX84-C3V9,215	Nexperia USA Inc.	3.9	±5%	250	90	900	-65 to 150	Active	SOT-23-3
BZX84-C3V9,235	NXP USA Inc.	3.9	±5%	250	90	900	-65 to 150	Active	SOT-23-3
BZX84B3V9-G3-08	Vishay General Semiconductor	3.9	±2%	300	90	—	-55 to 150	Active	SOT-23-3

Engineering Selection Recommendations

Primary Recommendation for Active Designs:

For new designs and ongoing production requiring the BZX84C3V9 specification, BZX84C3V9LT1G (onsemi) is the direct functional equivalent. This part maintains identical electrical characteristics (3.9 V, ±5% tolerance, 90 Ohms impedance, 900 mV forward voltage) while offering active product status, extended temperature range (-65°C to 150°C), and improved availability. The reduced power rating (225 mW vs. 350 mW) is acceptable for applications not requiring maximum dissipation headroom.

Automotive-Grade Alternative:

For applications requiring AEC-Q101 automotive qualification, SZBZX84C3V9LT1G (onsemi) provides identical electrical performance with automotive-grade certification and the highest inventory availability (39,100 pcs). This part is suitable for automotive and industrial applications with stringent reliability requirements.

Cross-Manufacturer Alternative with Enhanced Tolerance:

BZX84-A3V9,215 (Nexperia USA Inc.) offers superior voltage tolerance (±1% vs. ±5%), making it suitable for precision voltage reference applications. This part maintains all other critical parameters and carries AEC-Q101 qualification.

Direct Power-Matched Alternative:

CZRT55C3V9-G (Comchip Technology) matches the original 350 mW power specification while providing active status and extended temperature range (-65°C to 150°C). This part is appropriate for applications requiring maximum power dissipation capability.

Selection Criteria:

Standard applications: BZX84C3V9LT1G
Automotive/industrial: SZBZX84C3V9LT1G
Precision voltage reference: BZX84-A3V9,215
High-power dissipation: CZRT55C3V9-G

All recommended substitutes are RoHS3 compliant, REACH unaffected, and carry MSL 1 (Unlimited) moisture sensitivity rating.

Frequently Asked Questions (FAQ)

Q1: Can I use a 225 mW rated part to replace the 350 mW BZX84C3V9?

A: Yes, provided your application does not require the full 350 mW dissipation capability. The 225 mW parts (BZX84C3V9LT1G, SZBZX84C3V9 series) are electrically equivalent and suitable for standard voltage regulation and protection circuits. Verify your circuit's actual power dissipation requirements before substitution.

Q2: What is the difference between BZX84C3V9LT1G and SZBZX84C3V9LT1G?

A: Both parts are onsemi products with identical electrical specifications (3.9 V, ±5%, 225 mW, 90 Ohms). The SZBZX84C3V9LT1G carries AEC-Q101 automotive qualification and is intended for automotive and high-reliability applications. BZX84C3V9LT1G is the standard industrial-grade equivalent. Select based on application requirements.

Q3: Are all substitute parts compatible with the original SOT-23-3 footprint?

A: Yes. All listed substitute parts use the SOT-23-3 package (also designated TO-236-3 or SC-59). PCB footprints are mechanically and electrically compatible. No layout modifications are required.

Q4: Why does SZMMBZ5228BLT1G have a lower impedance (23 Ohms vs. 90 Ohms)?

A: SZMMBZ5228BLT1G is from a different Zener diode series with improved dynamic impedance characteristics. The lower impedance provides better voltage regulation stability under load transients. This part is suitable for applications benefiting from enhanced regulation performance, though it is not a direct specification match.

Q5: Can I substitute the BZX84C3V9 with BZX84B3V9-G3-08 from Vishay?

A: Yes, with considerations. BZX84B3V9-G3-08 maintains the 3.9 V specification and SOT-23-3 package but offers tighter tolerance (±2% vs. ±5%) and 300 mW power rating. The operating temperature range is -55°C to 150°C (matching the original). This part is suitable for applications requiring improved voltage accuracy.

Q6: What is the significance of the tolerance difference between ±5% and ±1%?

A: Tolerance specifies the allowable deviation of the Zener voltage from the nominal 3.9 V value. ±5% allows 3.705 V to 4.095 V; ±1% allows 3.861 V to 3.939 V. Use ±1% parts (BZX84-A3V9,215) for precision voltage reference circuits. Use ±5% parts for general regulation and protection applications.

Q7: Are all substitute parts RoHS3 compliant?

A: Yes. All listed substitute parts carry RoHS3 compliance status. The original BZX84C3V9 does not specify RoHS status due to its obsolete classification, but all active alternatives meet current RoHS3 requirements.

Q8: Which substitute part has the best availability?

A: SZBZX84C3V9LT1G (onsemi) has the highest inventory availability at 39,100 pcs. BZX84-C3V9,235 (NXP USA Inc.) has 20,654 pcs available. Both parts are suitable for high-volume production requirements.

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