FODM121E Optoisolator Equivalent & Substitute Parts

Part Overview

The FODM121E is a 3750Vrms optoisolator with transistor output manufactured by onsemi in a 4-SMD package. This component provides galvanic isolation for single-channel DC input applications with a maximum output current of 80mA and output voltage rating of 80V. The FODM121E is classified as obsolete, making equivalent and substitute parts necessary for new designs and ongoing production support. Substitute parts must maintain electrical compatibility across isolation voltage, output characteristics, and thermal operating range while accommodating different packaging formats and Current Transfer Ratio (CTR) specifications.

Key Parameters

Parameter	Value	Unit
Voltage - Isolation	3750	Vrms
Number of Channels	1	—
Output Type	Transistor	—
Voltage - Output (Max)	80	V
Current - Output / Channel	80	mA
Input Type	DC	—
Mounting Type	Surface Mount	—
Operating Temperature Range	-40 to 110	°C
Moisture Sensitivity Level (MSL)	1 (Unlimited)	—

Substitute Part Grouping Explanation

Substitution of the FODM121E is determined by strict adherence to the following electrical and mechanical parameters:

Primary Substitution Criteria:

Voltage - Isolation: Must equal 3750Vrms
Number of Channels: Must equal 1
Output Type: Must be Transistor
Voltage - Output (Max): Must equal or exceed 80V
Input Type: Must be DC
Mounting Type: Must be Surface Mount
Moisture Sensitivity Level: Must be 1 (Unlimited)

Secondary Compatibility Factors:

Current Transfer Ratio (CTR) ranges may vary; parts with different CTR specifications are functionally equivalent if all primary criteria are met
Package / Case format may differ (4-SMD Gull Wing, 4-SOIC, 4-Mini-Flat, 4-SOP) provided the supplier device package is compatible with board layout
Current - Output / Channel may be 50mA or 80mA; 50mA output is acceptable for applications requiring ≤50mA
Operating Temperature Range may extend beyond -40°C to 110°C; wider ranges are acceptable
Vce Saturation and Rise/Fall Time specifications may vary within acceptable limits for switching applications

Substitute Categories:

onsemi FODM121 Series (Same Manufacturer): FODM121A, FODM121R2, FODM121V — Direct packaging and product status variants
Broadcom HCPL-181 Series: HCPL-181-000E, HCPL-181-00AE, HCPL-181-00BE, HCPL-181-00CE, HCPL-181-00DE, HCPL-181-06BE — Alternative manufacturer with equivalent electrical specifications
Everlight EL357 Series: EL357ND(TA)-G — Alternative manufacturer with equivalent electrical specifications

Parameter Comparison

Part Number	Manufacturer	Product Status	Voltage - Isolation (Vrms)	CTR Min @ 5mA (%)	CTR Max @ 5mA (%)	Voltage - Output (Max) (V)	Current - Output (mA)	Operating Temp (°C)	Package / Case	RoHS Status
FODM121E	onsemi	Obsolete	3750	50	600	80	80	-40 to 110	4-SMD, Gull Wing	—
FODM121A	onsemi	Active	3750	100	300	80	80	-40 to 110	4-SMD, Gull Wing	ROHS3 Compliant
FODM121R2	onsemi	Active	3750	50	600	80	80	-40 to 110	4-SMD, Gull Wing	ROHS3 Compliant
FODM121V	onsemi	Active	3750	50	600	80	80	-40 to 110	4-SMD, Gull Wing	ROHS3 Compliant
EL357ND(TA)-G	Everlight Electronics Co Ltd	Active	3750	300	600	80	50	-55 to 110	4-SMD, Gull Wing	ROHS3 Compliant
HCPL-181-000E	Broadcom Limited	Active	3750	50	600	80	50	-55 to 100	4-SOIC (0.209", 5.30mm Width)	ROHS3 Compliant
HCPL-181-00AE	Broadcom Limited	Active	3750	80	160	80	50	-55 to 100	4-Mini-Flat	ROHS3 Compliant
HCPL-181-00BE	Broadcom Limited	Active	3750	130	260	80	50	-55 to 100	4-Mini-Flat	ROHS3 Compliant
HCPL-181-00CE	Broadcom Limited	Active	3750	200	400	80	50	-55 to 100	4-Mini-Flat	ROHS3 Compliant
HCPL-181-00DE	Broadcom Limited	Active	3750	300	600	80	50	-55 to 100	4-Mini-Flat	ROHS3 Compliant
HCPL-181-06BE	Broadcom Limited	Active	3750	130	260	80	50	-55 to 100	4-Mini-Flat	ROHS3 Compliant

Engineering Selection Recommendations

onsemi FODM121 Series (Recommended for Direct Replacement):

FODM121A, FODM121R2, and FODM121V are active products from the same manufacturer with identical electrical isolation, output voltage, and thermal specifications as the obsolete FODM121E
All three variants maintain 3750Vrms isolation and 80V maximum output voltage
FODM121A offers narrower CTR range (100–300%) suitable for applications requiring tighter gain control
FODM121R2 and FODM121V match the FODM121E CTR specification (50–600%) for applications with broader tolerance requirements
All onsemi variants are ROHS3 compliant and carry MSL 1 rating
Packaging differences: FODM121A (Tube), FODM121R2 (Tape & Reel), FODM121V (Box) — select based on procurement and assembly requirements

Broadcom HCPL-181 Series (Alternative Manufacturer):

All HCPL-181 variants maintain 3750Vrms isolation and 80V maximum output voltage
Output current is reduced to 50mA (vs. 80mA on FODM121E); suitable for applications requiring ≤50mA
Operating temperature range is -55°C to 100°C (vs. -40°C to 110°C); verify compatibility for extreme temperature applications
Package options include 4-SOIC (HCPL-181-000E) and 4-Mini-Flat (HCPL-181-00AE, -00BE, -00CE, -00DE, -06BE)
CTR variants available: 50–600% (HCPL-181-000E, -00DE), 80–160% (HCPL-181-00AE), 130–260% (HCPL-181-00BE, -06BE), 200–400% (HCPL-181-00CE)
All HCPL-181 parts are ROHS3 compliant and carry MSL 1 rating
High inventory availability across all variants

Everlight EL357ND(TA)-G (Alternative Manufacturer):

Maintains 3750Vrms isolation and 80V maximum output voltage
Output current is 50mA (vs. 80mA on FODM121E); suitable for applications requiring ≤50mA
Operating temperature range is -55°C to 110°C, extending the lower limit for cold environment applications
CTR range is 300–600%, providing higher and narrower gain specification
Package is 4-SOP (2.54mm), differing from FODM121E 4-SMD Gull Wing; board layout compatibility must be verified
ROHS3 compliant with MSL 1 rating

Product Status Consideration: All recommended substitutes are active products with ongoing manufacturer support, ensuring long-term availability and supply chain stability compared to the obsolete FODM121E.

Frequently Asked Questions (FAQ)

Q: Can FODM121A, FODM121R2, or FODM121V be used as direct replacements for FODM121E? A: Yes. All three onsemi variants meet the primary substitution criteria: 3750Vrms isolation, single-channel transistor output, 80V maximum output voltage, 80mA output current, and -40°C to 110°C operating range. The differences are product status (active vs. obsolete), packaging format (Tube, Tape & Reel, Box), and CTR specification range. FODM121A has a narrower CTR range (100–300%), while FODM121R2 and FODM121V match the FODM121E CTR range (50–600%).

Q: What is the impact of reduced output current (50mA vs. 80mA) when using Broadcom HCPL-181 or Everlight EL357ND(TA)-G? A: The HCPL-181 and EL357ND(TA)-G are rated for 50mA maximum output current, compared to 80mA on the FODM121E. These parts are suitable for applications requiring output currents up to 50mA. If your application requires output currents between 50mA and 80mA, use onsemi FODM121 variants (FODM121A, FODM121R2, FODM121V) instead.

Q: Are there package compatibility considerations when switching between FODM121E and substitute parts? A: Yes. The FODM121E uses a 4-SMD Gull Wing package. onsemi FODM121 variants (FODM121A, FODM121R2, FODM121V) use the same 4-SMD Gull Wing package and are pin-compatible. Broadcom HCPL-181 parts use either 4-SOIC or 4-Mini-Flat packages, requiring PCB layout verification. Everlight EL357ND(TA)-G uses a 4-SOP (2.54mm) package, also requiring layout verification. Consult component datasheets for pinout and footprint compatibility.

Q: How do Current Transfer Ratio (CTR) specifications affect part selection? A: CTR determines the ratio of output current to input current and affects circuit gain. The FODM121E has a CTR range of 50–600% at 5mA input. Substitute parts offer different CTR ranges: FODM121A (100–300%), HCPL-181-00AE (80–160%), HCPL-181-00BE and -06BE (130–260%), HCPL-181-00CE (200–400%), HCPL-181-000E and -00DE (50–600%), and EL357ND(TA)-G (300–600%). Select a substitute with a CTR range that matches your circuit design requirements. Narrower CTR ranges provide tighter gain control; wider ranges offer greater component tolerance.

Q: What is the difference between FODM121R2 and FODM121V packaging? A: FODM121R2 is supplied in Tape & Reel (TR) format, suitable for high-volume automated assembly. FODM121V is supplied in Box format, suitable for lower-volume applications or manual assembly. Both parts are electrically identical with 50–600% CTR range and active product status. Select based on your procurement and assembly process requirements.

Q: Are all substitute parts RoHS3 compliant? A: All recommended substitute parts (FODM121A, FODM121R2, FODM121V, EL357ND(TA)-G, and all HCPL-181 variants) are ROHS3 compliant. The original FODM121E does not list RoHS status. If RoHS3 compliance is required for your application, use any of the active substitute parts listed.

Q: What is the operating temperature range difference, and does it matter? A: The FODM121E operates from -40°C to 110°C. Broadcom HCPL-181 parts operate from -55°C to 100°C (lower minimum, higher maximum). Everlight EL357ND(TA)-G operates from -55°C to 110°C (lower minimum, same maximum). If your application requires operation below -40°C, use HCPL-181 or EL357ND(TA)-G. If your application requires operation above 100°C, use onsemi FODM121 variants or EL357ND(TA)-G.

Q: Can I use HCPL-181-00BE and HCPL-181-06BE interchangeably? A: Yes. Both parts have identical electrical specifications: 3750Vrms isolation, 130–260% CTR range, 80V maximum output voltage, 50mA output current, and -55°C to 100°C operating range. Both use 4-Mini-Flat packages. The difference is packaging format (both are Cut Tape & Digi-Reel). They are functionally equivalent and can be used interchangeably.

Request Quote (Ships tomorrow)

Part Number

Quantity

Company

Contact Name

E-mail

Message