FDH700 Equivalent & Substitute Parts

Part Overview

The FDH700 is a general-purpose rectifier diode manufactured by onsemi, rated for 20 V DC reverse voltage and 150 mA average rectified current in a DO-35 through-hole package. This component is classified as obsolete, making identification of functionally equivalent alternatives necessary for ongoing design support and procurement continuity. The FDH700 operates across a junction temperature range of -65°C to 175°C and exhibits small-signal switching characteristics suitable for general rectification and signal detection applications.

Key Parameters

Parameter	Value	Unit
Voltage - DC Reverse (Vr) (Max)	20	V
Current - Average Rectified (Io)	150	mA
Voltage - Forward (Vf) (Max) @ If	1.25 V @ 50 mA	V
Reverse Recovery Time (trr)	900	ps
Current - Reverse Leakage @ Vr	50	nA @ 20 V
Capacitance @ Vr, F	1.5	pF @ 0V, 1MHz
Package / Case	DO-204AH, DO-35, Axial	—
Operating Temperature - Junction	-65 to 175	°C
Mounting Type	Through Hole	—
Product Status	Obsolete	—

Substitute Part Grouping Explanation

Substitution of the FDH700 is determined by compatibility across the following critical parameters:

Mandatory Compatibility Criteria:

Package / Case: DO-35 through-hole axial configuration
Mounting Type: Through-hole
Voltage - DC Reverse (Vr) (Max): Must equal or exceed 20 V
Current - Average Rectified (Io): Must equal or exceed 150 mA
Speed Classification: Small signal (≤ 200 mA)
Operating Temperature Range: Must encompass or exceed -65°C to 175°C

Functional Equivalence Basis: The 1N4448 qualifies as a substitute because it maintains the same DO-35 package geometry, exceeds the voltage and current ratings of the FDH700, operates within the required temperature range, and shares identical speed classification. The 1N4448 provides enhanced electrical performance with higher reverse voltage (75 V vs. 20 V) and increased current capacity (200 mA vs. 150 mA), making it suitable for applications where the FDH700 was previously specified.

Parameter Comparison

Parameter	FDH700 (onsemi)	1N4448 (Microchip Technology)	Unit
Voltage - DC Reverse (Vr) (Max)	20	75	V
Current - Average Rectified (Io)	150	200	mA
Voltage - Forward (Vf) (Max) @ If	1.25 V @ 50 mA	1 V @ 100 mA	V
Reverse Recovery Time (trr)	900	4	ps / ns
Current - Reverse Leakage @ Vr	50 nA @ 20 V	25 nA @ 20 V	nA
Package / Case	DO-35	DO-35	—
Operating Temperature - Junction	-65 to 175	-65 to 150	°C
Mounting Type	Through Hole	Through Hole	—
Speed Classification	Small Signal ≤ 200mA	Small Signal ≤ 200mA	—

Engineering Selection Recommendations

1N4448 Substitution Suitability:

The 1N4448 is electrically and mechanically compatible with the FDH700 for direct replacement in through-hole PCB applications. The substitute part exceeds all minimum electrical requirements: reverse voltage rating is 3.75 times higher (75 V vs. 20 V), average rectified current capacity is 33% greater (200 mA vs. 150 mA), and forward voltage drop is lower (1 V vs. 1.25 V at comparable current levels).

Status Considerations:

The FDH700 is classified as obsolete, while the 1N4448 is listed as discontinued at DiGi Electronics. Both parts share identical REACH compliance status (REACH Unaffected) and ECCN classification (EAR99). The 1N4448 is non-compliant with RoHS directives, whereas RoHS status for the FDH700 is not specified in the provided data.

Temperature Range Limitation:

The 1N4448 maximum junction temperature is 150°C, which is 25°C lower than the FDH700 specification of 175°C. Applications requiring operation at junction temperatures between 150°C and 175°C require alternative solutions.

Reverse Recovery Time Trade-off:

The 1N4448 exhibits faster reverse recovery (4 ns vs. 900 ps), indicating improved switching performance for high-frequency applications, though this represents a different technology generation.

Frequently Asked Questions (FAQ)

Q: Can the 1N4448 be used as a direct replacement for the FDH700 in all applications?

A: The 1N4448 is mechanically and electrically compatible for most applications. However, designs operating at junction temperatures above 150°C require verification against the 1N4448 maximum rating of 150°C, as the FDH700 supports operation to 175°C.

Q: What is the significance of the DO-35 package specification?

A: The DO-35 package is a standardized through-hole axial lead configuration. Both the FDH700 and 1N4448 use this identical package, ensuring mechanical compatibility with existing PCB layouts without requiring board redesign.

Q: Why does the 1N4448 have a higher reverse voltage rating than the FDH700?

A: The 1N4448 is rated for 75 V reverse voltage compared to the FDH700's 20 V rating. This higher rating provides design margin and allows the 1N4448 to function in applications with higher voltage transients or overvoltage conditions.

Q: Are there compliance differences between these parts?

A: Both parts share REACH Unaffected and EAR99 ECCN status. The 1N4448 is RoHS non-compliant. RoHS compliance status for the FDH700 is not provided in the available data.

Q: What does "small signal" classification mean for these diodes?

A: Small signal classification indicates average rectified current capacity of 200 mA or less. Both the FDH700 (150 mA) and 1N4448 (200 mA) fall within this category, distinguishing them from power rectifier diodes with higher current ratings.

Q: How do reverse recovery times affect circuit performance?

A: Reverse recovery time (trr) determines how quickly a diode transitions from conducting to blocking state. The 1N4448's 4 ns recovery time is faster than the FDH700's 900 ps specification, resulting in reduced switching losses in high-frequency applications.

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