HMA121B Optoisolator Equivalent & Substitute Parts

Part Overview

The HMA121B is a 3750Vrms optoisolator with transistor output manufactured by onsemi in a 4-SMD package. This component is classified as obsolete, making equivalent and substitute parts necessary for ongoing design support and production continuity. The HMA121B provides single-channel isolation suitable for DC input applications requiring high voltage isolation with moderate current transfer ratios (50–150% @ 5mA).

Key Parameters

Parameter	Value
Voltage - Isolation	3750Vrms
Number of Channels	1
Current Transfer Ratio (Min)	50% @ 5mA
Current Transfer Ratio (Max)	150% @ 5mA
Output Type	Transistor
Voltage - Output (Max)	80V
Current - Output / Channel	80mA
Vce Saturation (Max)	400mV
Operating Temperature	-40°C ~ 100°C
Mounting Type	Surface Mount
Package / Case	4-SMD, Gull Wing
Input Type	DC

Substitute Part Grouping Explanation

Substitution for the HMA121B is determined by the following critical parameters:

Voltage - Isolation: Must equal 3750Vrms
Number of Channels: Must equal 1
Output Type: Must be Transistor
Input Type: Must be DC
Voltage - Output (Max): Must equal or exceed 80V
Current - Output / Channel: Must equal or exceed 80mA (primary requirement for HMA121B)
Mounting Type: Surface Mount
Operating Temperature Range: Must encompass or exceed -40°C ~ 100°C

Substitute parts are grouped into two categories:

Direct Functional Equivalent: FODM121B (onsemi) — identical electrical specifications with active product status and extended temperature range (-40°C ~ 110°C).

Similar Functional Equivalents: Parts meeting all critical isolation, channel, output type, and mounting requirements but with variations in current transfer ratio, package style, or output current capability. These include HCPL-181 series (Broadcom), EL357ND(TA)-G (Everlight), and LTV-356T (Lite-On).

Parameter Comparison

Part Number	Manufacturer	Voltage - Isolation	CTR Min @ 5mA	CTR Max @ 5mA	Output Current	Vce Sat (Max)	Temp Range	Package	Status
HMA121B	onsemi	3750Vrms	50%	150%	80mA	400mV	-40°C ~ 100°C	4-SMD	Obsolete
FODM121B	onsemi	3750Vrms	50%	150%	80mA	400mV	-40°C ~ 110°C	4-SMD	Active
EL357ND(TA)-G	Everlight	3750Vrms	300%	600%	50mA	200mV	-55°C ~ 110°C	4-SOP	Active
HCPL-181-000E	Broadcom	3750Vrms	50%	600%	50mA	200mV	-55°C ~ 100°C	4-SOIC	Active
HCPL-181-00AE	Broadcom	3750Vrms	80%	160%	50mA	200mV	-55°C ~ 100°C	4-Mini-Flat	Active
HCPL-181-00BE	Broadcom	3750Vrms	130%	260%	50mA	200mV	-55°C ~ 100°C	4-Mini-Flat	Active
HCPL-181-00CE	Broadcom	3750Vrms	200%	400%	50mA	200mV	-55°C ~ 100°C	4-Mini-Flat	Active
HCPL-181-00DE	Broadcom	3750Vrms	300%	600%	50mA	200mV	-55°C ~ 100°C	4-Mini-Flat	Active
HCPL-181-06BE	Broadcom	3750Vrms	130%	260%	50mA	200mV	-55°C ~ 100°C	4-Mini-Flat	Active
HCPL-181-06DE	Broadcom	3750Vrms	300%	600%	50mA	200mV	-55°C ~ 100°C	4-Mini-Flat	Active
LTV-356T	Lite-On	3750Vrms	50%	600%	50mA	200mV	-55°C ~ 110°C	4-SOP	Active

Engineering Selection Recommendations

Primary Recommendation: FODM121B

FODM121B is the direct functional equivalent of HMA121B, manufactured by onsemi with identical electrical specifications. It maintains the same current transfer ratio range (50–150% @ 5mA), output current capability (80mA), and saturation voltage (400mV). FODM121B holds active product status and extends the operating temperature range to -110°C, providing superior long-term availability and compliance. RoHS3 compliance is confirmed.

Secondary Recommendations for Package-Constrained Designs

When 4-SMD package footprint cannot be accommodated:

HCPL-181-00BE or HCPL-181-06BE (Broadcom, 4-Mini-Flat): Current transfer ratio 130–260% @ 5mA, reduced output current (50mA), lower saturation voltage (200mV). Suitable for applications not requiring 80mA output current. RoHS3 compliant, active status.
LTV-356T (Lite-On, 4-SOP): Current transfer ratio 50–600% @ 5mA, reduced output current (50mA), extended temperature range (-55°C ~ 110°C). RoHS3 compliant, active status.

Considerations for Output Current Derating

EL357ND(TA)-G and HCPL-181 series provide maximum output current of 50mA, compared to HMA121B's 80mA. Applications requiring the full 80mA output current must use FODM121B or confirm that the substitute part's 50mA rating is sufficient for the circuit design.

Frequently Asked Questions (FAQ)

Q: Can HCPL-181-00BE directly replace HMA121B in existing PCB layouts?

A: No. HCPL-181-00BE uses a 4-Mini-Flat package, while HMA121B uses 4-SMD. PCB footprints are incompatible. FODM121B maintains the 4-SMD footprint for direct replacement. Alternative packages require PCB redesign.

Q: What is the significance of Current Transfer Ratio (CTR) differences?

A: CTR determines the output current for a given input current. HMA121B specifies 50–150% CTR @ 5mA. Substitutes with higher CTR (e.g., HCPL-181-00DE at 300–600%) provide greater output current for the same input, potentially requiring circuit recalibration. Lower CTR substitutes may require increased input current to achieve equivalent output.

Q: Is FODM121B a direct drop-in replacement for HMA121B?

A: Yes, for electrical and mechanical compatibility. FODM121B matches HMA121B's isolation voltage, channel count, output type, package, and current ratings. The extended temperature range (-40°C ~ 110°C vs. -40°C ~ 100°C) provides additional operational margin. Active product status ensures long-term supply availability.

Q: Why do some substitutes have lower output current (50mA vs. 80mA)?

A: Package and die design differences result in different current handling capabilities. HCPL-181 and EL357 series are optimized for different applications. Designs requiring 80mA output must use FODM121B or confirm that 50mA is adequate through circuit analysis.

Q: Are all listed substitutes RoHS3 compliant?

A: FODM121B, HCPL-181 series, EL357ND(TA)-G, and LTV-356T are all RoHS3 compliant. HMA121B (obsolete) does not carry RoHS3 certification. Compliance status is confirmed in product documentation.

Q: What is the difference between HCPL-181-00BE and HCPL-181-06BE?

A: Both use 4-Mini-Flat packages with identical electrical specifications (130–260% CTR @ 5mA, 50mA output, 200mV saturation). The suffix difference (-00 vs. -06) indicates internal design variants. Both are functionally equivalent for substitution purposes.

Q: Can I use EL357ND(TA)-G if my circuit only requires 50mA output?

A: Yes, if your circuit design confirms that 50mA output current is sufficient. EL357ND(TA)-G provides 3750Vrms isolation, single-channel transistor output, and active product status. The 4-SOP package requires PCB redesign. Higher CTR (300–600%) may require input current adjustment.

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