FDLL4151 Equivalent & Substitute Parts

Part Overview

The FDLL4151 is a general-purpose rectifier diode rated for 75 V DC reverse voltage and 200 mA average rectified current in a surface mount SOD-80 (Mini-MELF) package. Manufactured by onsemi, this component is classified as obsolete. Due to its obsolete status, equivalent substitute parts from active manufacturers are necessary to maintain design continuity and ensure long-term component availability for new production and field replacements.

Key Parameters

Parameter	Value
Voltage - DC Reverse (Vr) (Max)	75 V
Current - Average Rectified (Io)	200 mA
Voltage - Forward (Vf) (Max) @ If	1 V @ 50 mA
Reverse Recovery Time (trr)	4 ns
Current - Reverse Leakage @ Vr	50 nA @ 50 V
Capacitance @ Vr, F	4 pF @ 0 V, 1 MHz
Mounting Type	Surface Mount
Package / Case	DO-213AC, MINI-MELF, SOD-80
Operating Temperature - Junction	-65°C ~ 200°C
Product Status	Obsolete

Substitute Part Grouping Explanation

Substitution of the FDLL4151 is determined by the following critical electrical and mechanical parameters:

Primary Substitution Criteria:

Voltage - DC Reverse (Vr) (Max): Must equal or exceed 75 V
Current - Average Rectified (Io): Must equal or exceed 200 mA
Mounting Type: Surface Mount
Speed Classification: Small Signal ≤ 200 mA (Io), Any Speed

Secondary Compatibility Factors:

Package / Case: SOD-80 (Mini-MELF) preferred for direct mechanical compatibility; DO-213AA (Glass) acceptable with PCB layout verification
Operating Temperature Range: Minimum -65°C to +175°C required
Reverse Recovery Time (trr): Lower values indicate faster switching performance
Forward Voltage (Vf): Lower values indicate reduced power dissipation

Substitute parts are grouped into two categories:

Category A - Direct Electrical Equivalents (75 V Rating): Parts meeting or exceeding the 75 V reverse voltage specification with 200 mA current rating and compatible surface mount packaging.

Category B - Functional Equivalents (70 V Rating): Parts with 70 V reverse voltage rating, suitable for applications where the 5 V margin reduction is acceptable within circuit design constraints.

Category C - Voltage-Elevated Equivalents (80 V Rating): Parts exceeding the 75 V specification, providing additional voltage margin for circuit protection.

Category D - Reduced-Rating Equivalents (50 V Rating): Parts with lower voltage ratings, suitable only for applications operating below 50 V maximum reverse voltage.

Parameter Comparison

Parameter	FDLL4151 (Main)	1N4148UR-1	1N5194UR	CDLL4148	CDLL483B	LL4151-GS08
Manufacturer	onsemi	Microchip Technology	Microchip Technology	Microchip Technology	Microchip Technology	Vishay General Semiconductor
Voltage - DC Reverse (Vr) (Max)	75 V	75 V	70 V	75 V	80 V	50 V
Current - Average Rectified (Io)	200 mA	200 mA	200 mA	200 mA	200 mA	150 mA
Voltage - Forward (Vf) (Max) @ If	1 V @ 50 mA	1.2 V @ 100 mA	1 V @ 100 mA	1 V @ 200 mA	1 V @ 100 mA	1 V @ 50 mA
Reverse Recovery Time (trr)	4 ns	20 ns	Not specified	20 ns	Not specified	4 ns
Current - Reverse Leakage @ Vr	50 nA @ 50 V	500 nA @ 75 V	25 nA @ 70 V	500 nA @ 75 V	100 µA @ 80 V	50 nA @ 50 V
Capacitance @ Vr, F	4 pF @ 0 V, 1 MHz	Not specified	Not specified	4 pF @ 0 V, 1 MHz	Not specified	2 pF @ 0 V, 1 MHz
Mounting Type	Surface Mount	Surface Mount	Surface Mount	Surface Mount	Surface Mount	Surface Mount
Package / Case	DO-213AC, MINI-MELF, SOD-80	DO-213AA (Glass)	DO-213AA (Glass)	DO-213AA	DO-213AA	DO-213AC, MINI-MELF, SOD-80
Operating Temperature - Junction	-65°C ~ 200°C	-65°C ~ 175°C	-65°C ~ 175°C	-65°C ~ 175°C	-65°C ~ 175°C	-65°C ~ 175°C
Product Status	Obsolete	Active	Active	Active	Active	Active
Inventory Availability	700 Pcs	15810 Pcs	900 Pcs	699 Pcs	1088 Pcs	42600 Pcs

Engineering Selection Recommendations

Primary Recommendation: CDLL4148

The CDLL4148 from Microchip Technology provides direct electrical equivalence to the FDLL4151 with identical 75 V reverse voltage and 200 mA current ratings. This part is active in production status, ensuring long-term availability. The CDLL4148 matches the forward voltage specification at 1 V @ 200 mA and maintains the same capacitance value of 4 pF @ 0 V, 1 MHz. The operating temperature range of -65°C to 175°C covers the FDLL4151 specification except for the upper limit, which is reduced by 25°C. The DO-213AA package is mechanically compatible with SOD-80 applications through standard PCB layout adaptation.

Secondary Recommendation: 1N4148UR-1

The 1N4148UR-1 from Microchip Technology maintains the 75 V reverse voltage and 200 mA current specifications. This part offers the highest inventory availability (15,810 pieces) among active substitutes. The forward voltage is specified at 1.2 V @ 100 mA, representing a 0.2 V increase compared to the FDLL4151. The reverse recovery time of 20 ns is longer than the FDLL4151 specification of 4 ns, which may impact high-frequency switching applications. The DO-213AA package requires PCB layout verification for mechanical compatibility.

Tertiary Recommendation: CDLL483B

The CDLL483B from Microchip Technology provides voltage margin above the FDLL4151 specification with an 80 V reverse voltage rating. This part maintains the 200 mA current rating and 1 V forward voltage @ 100 mA. The reverse leakage current of 100 µA @ 80 V is significantly higher than the FDLL4151 specification of 50 nA @ 50 V, which may increase power dissipation in low-leakage applications. The DO-213AA package requires PCB layout verification.

Alternative Recommendation: LL4151-GS08

The LL4151-GS08 from Vishay General Semiconductor provides the same SOD-80 package as the FDLL4151, eliminating mechanical compatibility concerns. This part is RoHS3 compliant and offers the highest inventory availability (42,600 pieces). However, the 50 V reverse voltage rating and 150 mA current rating represent reductions from the FDLL4151 specification. This part is suitable only for applications operating within these reduced electrical limits.

Not Recommended: 1N5194UR

The 1N5194UR from Microchip Technology has a 70 V reverse voltage rating, which is 5 V below the FDLL4151 specification. While the 200 mA current rating is maintained, the reduced voltage margin may be insufficient for circuits designed to the full 75 V specification.

Frequently Asked Questions (FAQ)

Q: Can the CDLL4148 directly replace the FDLL4151 without PCB modifications?

A: The CDLL4148 uses the DO-213AA package while the FDLL4151 uses SOD-80. Both are surface mount packages with similar footprints, but PCB layout verification is required to confirm pad spacing and component placement compatibility. Consult the respective package datasheets for exact dimensions.

Q: What is the significance of the 4 ns reverse recovery time in the FDLL4151 compared to the 20 ns in the 1N4148UR-1?

A: Reverse recovery time (trr) determines how quickly the diode transitions from conducting to blocking state. The FDLL4151 specification of 4 ns indicates faster switching performance, which is critical in high-frequency applications. The 1N4148UR-1 with 20 ns trr may introduce switching delays in circuits operating above several megahertz. Application frequency requirements determine whether this difference is acceptable.

Q: Why does the CDLL483B have a 100 µA reverse leakage current while the FDLL4151 specifies 50 nA?

A: Reverse leakage current is the small current that flows through a reverse-biased diode. The CDLL483B specification of 100 µA @ 80 V is approximately 2,000 times higher than the FDLL4151 specification of 50 nA @ 50 V. This difference reflects different semiconductor manufacturing processes and doping profiles. In applications requiring low leakage, such as precision analog circuits or high-impedance signal paths, the CDLL483B may introduce unacceptable noise or signal degradation.

Q: Is the LL4151-GS08 suitable for all FDLL4151 applications?

A: The LL4151-GS08 has a 50 V reverse voltage rating and 150 mA current rating, both lower than the FDLL4151 specification of 75 V and 200 mA. This part is suitable only for applications where the circuit operates within these reduced electrical limits. If the circuit is designed for the full 75 V and 200 mA specifications, the LL4151-GS08 will not provide adequate performance margin and may fail under specified operating conditions.

Q: What is the impact of the reduced operating temperature range (-65°C to 175°C) in substitute parts compared to the FDLL4151 (-65°C to 200°C)?

A: The FDLL4151 specifies a maximum junction temperature of 200°C, while all substitute parts specify 175°C. This 25°C reduction may impact applications operating at elevated ambient temperatures or with high power dissipation. Thermal analysis is required to confirm that the substitute part's maximum junction temperature is not exceeded under worst-case operating conditions.

Q: Can the 1N5194UR be used in a circuit designed for 75 V operation?

A: The 1N5194UR has a 70 V reverse voltage rating, which is 5 V below the FDLL4151 specification. While this part may function in many applications, it provides no safety margin above the rated voltage. Any transient overvoltage or design tolerance stack-up that approaches 75 V could cause the diode to exceed its rated voltage and fail. Use of this part is not recommended for circuits specified at 75 V.

Q: What packaging considerations apply when substituting DO-213AA parts for SOD-80?

A: Both DO-213AC (SOD-80) and DO-213AA are surface mount packages with similar form factors but different mechanical specifications. The DO-213AA package uses a glass body while SOD-80 uses a ceramic body. PCB pad spacing, component height, and solder reflow profiles may differ. Verify that the substitute part's package dimensions are compatible with the PCB design before implementation. Consult the manufacturer's package drawings for exact specifications.

Q: Why is the CDLL4148 recommended over the 1N4148UR-1 despite lower inventory availability?

A: The CDLL4148 provides superior electrical equivalence to the FDLL4151 with matching forward voltage (1 V @ 200 mA) and capacitance (4 pF @ 0 V, 1 MHz) specifications. The 1N4148UR-1 has a higher forward voltage (1.2 V @ 100 mA) and longer reverse recovery time (20 ns), which may impact circuit performance in sensitive applications. While inventory availability is a practical consideration, electrical equivalence is the primary substitution criterion.

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