4N37 Optoisolator Equivalent & Substitute Parts

Part Overview

The 4N37 is a single-channel optoisolator with transistor output and base connection, manufactured by Vishay Semiconductor Opto Division. This component provides 5000Vrms isolation voltage and is designed for DC input applications requiring galvanic isolation with transistor-based output control. The part is active and in production, with 19,066 units currently in stock. Substitute parts are identified when equivalent electrical performance and mechanical compatibility are required due to supply constraints, design flexibility, or application-specific parameter optimization.

Key Parameters

Parameter	Value	Unit	Significance for Substitution
Voltage - Isolation	5000	Vrms	Primary isolation specification; substitutes must meet or exceed this value
Number of Channels	1	Channel	Fixed requirement; all substitutes must be single-channel
Current Transfer Ratio (Min)	100% @ 10mA	%	Input-to-output current transfer efficiency; critical for circuit design
Output Type	Transistor with Base	-	Output configuration; must match for pin compatibility
Voltage - Output (Max)	30	V	Maximum collector voltage rating
Current - Output / Channel	50	mA	Maximum output current per channel
Package / Case	6-DIP (0.300", 7.62mm)	-	Physical form factor; must be identical for PCB compatibility
Operating Temperature	-55°C ~ 100°C	°C	Thermal operating range
Mounting Type	Through Hole	-	Assembly method; all substitutes must be through-hole
RoHS Status	ROHS3 Compliant	-	Environmental compliance requirement

Substitute Part Grouping Explanation

Substitute parts for the 4N37 are classified into two functional groups based on isolation voltage specification:

Group A: 5000Vrms Isolation Equivalents These parts maintain the exact 5000Vrms isolation voltage of the 4N37 and are direct functional replacements. Parts in this group: 4N36 (Texas Instruments).

Group B: Enhanced Isolation Voltage (5300Vrms) Substitutes These parts exceed the 4N37 isolation specification with 5300Vrms isolation, providing superior isolation margin. Parts in this group: H11A2X, H11A3X, MCT2EX (all Isocom Components).

Group C: Lower Isolation Voltage (7.5Vpk) Substitutes These parts operate at reduced isolation voltage of 7.5Vpk and are suitable only for applications where lower isolation voltage is acceptable. Parts in this group: 4N36X, H11A5X, MCT2200X, MCT2201X, MCT2202X, MCT2X (all Isocom Components).

All substitute parts share the following mandatory compatibility criteria with the 4N37:

Single-channel configuration
Transistor output with base connection
6-DIP through-hole package (0.300", 7.62mm)
Operating temperature range -55°C ~ 100°C
Output voltage rating 30V maximum
Output current rating 50mA per channel
Forward voltage (Vf) 1.2V to 1.3V typical
DC forward current (If) 50mA to 60mA maximum
RoHS3 compliance
MSL Level 1 (Unlimited moisture sensitivity)

Parameter Comparison

Part Number	Manufacturer	Isolation Voltage	CTR Min @ 10mA	Turn On/Off Time (Typ)	Rise/Fall Time (Typ)	Vce Sat (Max)	RoHS Status	Inventory
4N37	Vishay Semiconductor	5000Vrms	100%	10µs, 10µs	-	-	ROHS3 Compliant	19,066 Pcs
4N36	Texas Instruments	5000Vrms	100%	10µs, 10µs	-	-	RoHS non-compliant	100,400 Pcs
4N36X	Isocom Components	7.5Vpk	100%	-	2µs, 2µs	300mV	ROHS3 Compliant	977 Pcs
H11A2X	Isocom Components	5300Vrms	20%	-	2µs, 2µs	400mV	ROHS3 Compliant	1,290 Pcs
H11A3X	Isocom Components	5300Vrms	20%	-	2µs, 2µs	400mV	ROHS3 Compliant	1,771 Pcs
H11A5X	Isocom Components	7.5Vpk	30%	-	2µs, 2µs	400mV	ROHS3 Compliant	1,203 Pcs
MCT2200X	Isocom Components	7.5Vpk	20%	10µs, 10µs (Max)	-	400mV	ROHS3 Compliant	813 Pcs
MCT2201X	Isocom Components	7.5Vpk	100%	10µs, 10µs (Max)	-	400mV	ROHS3 Compliant	748 Pcs
MCT2202X	Isocom Components	7.5Vpk	63% to 125%	10µs, 10µs (Max)	-	400mV	ROHS3 Compliant	839 Pcs
MCT2EX	Isocom Components	5300Vrms	50%	3µs, 3µs	-	400mV	ROHS3 Compliant	1,750 Pcs
MCT2X	Isocom Components	7.5Vpk	20%	3µs, 3µs	-	400mV	ROHS3 Compliant	778 Pcs

Engineering Selection Recommendations

For Direct Replacement (5000Vrms Isolation Requirement):

The 4N36 (Texas Instruments) is the only direct electrical equivalent maintaining 5000Vrms isolation voltage and 100% minimum CTR. However, the 4N36 is RoHS non-compliant, which may restrict use in regulated applications or regions with environmental compliance mandates. If RoHS3 compliance is mandatory, the 4N37 remains the preferred choice despite lower inventory availability.

For Enhanced Isolation Margin (5300Vrms Isolation):

The H11A2X, H11A3X, and MCT2EX provide superior isolation voltage (5300Vrms) compared to the 4N37 specification. These parts are suitable for applications requiring additional isolation safety margin. However, H11A2X and H11A3X exhibit reduced CTR (20% minimum), which may require circuit design adjustment. MCT2EX offers 50% minimum CTR with faster switching times (3µs vs. 10µs), making it suitable for higher-speed applications. All three parts are RoHS3 compliant.

For Cost-Optimized or Lower-Isolation Applications (7.5Vpk Isolation):

Parts in Group C (4N36X, H11A5X, MCT2200X, MCT2201X, MCT2202X, MCT2X) operate at 7.5Vpk isolation voltage and are suitable only for applications where isolation voltage requirements are significantly lower than 5000Vrms. These parts are not recommended as substitutes for the 4N37 in high-voltage isolation circuits. MCT2201X and MCT2202X maintain 100% and 63-125% CTR respectively, matching the 4N37 current transfer performance.

Compliance Considerations:

All substitute parts except 4N36 are RoHS3 compliant and REACH unaffected, matching the 4N37 environmental compliance profile. The 4N36 is RoHS non-compliant and REACH affected, restricting its use in regulated markets.

Frequently Asked Questions (FAQ)

Q: Can the 4N36 be used as a direct replacement for the 4N37?

A: The 4N36 is electrically equivalent to the 4N37, maintaining identical 5000Vrms isolation voltage, 100% minimum CTR, and 10µs switching times. However, the 4N36 is RoHS non-compliant, which may violate environmental regulations in certain jurisdictions. Verify compliance requirements before substitution.

Q: What is the difference between Group A and Group B substitutes?

A: Group A (4N36) maintains the 4N37's 5000Vrms isolation specification. Group B (H11A2X, H11A3X, MCT2EX) provides enhanced 5300Vrms isolation, offering additional safety margin but with reduced or different current transfer ratios. Group B parts are suitable for applications requiring higher isolation voltage than specified.

Q: Are the 7.5Vpk isolation parts (Group C) suitable for the 4N37 application?

A: Group C parts operate at significantly lower isolation voltage (7.5Vpk vs. 5000Vrms) and are not recommended as substitutes for the 4N37 in high-voltage isolation circuits. These parts are suitable only for applications with substantially lower isolation requirements.

Q: Do all substitute parts use the same 6-DIP package as the 4N37?

A: Yes. All listed substitute parts use the 6-DIP (0.300", 7.62mm) through-hole package, ensuring mechanical and pin compatibility with the 4N37. No PCB layout modifications are required for package substitution.

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

A: CTR determines the input-to-output current transfer efficiency. The 4N37 specifies 100% minimum CTR at 10mA input. Substitutes with lower CTR (such as H11A2X at 20%) require higher input current to achieve equivalent output current, potentially affecting circuit design. Verify CTR requirements before selecting lower-CTR alternatives.

Q: Which substitute offers the fastest switching performance?

A: MCT2EX and MCT2X offer the fastest switching times at 3µs turn-on/turn-off, compared to the 4N37's 10µs specification. These parts are suitable for higher-frequency switching applications. However, MCT2EX operates at 5300Vrms isolation while MCT2X operates at 7.5Vpk isolation.

Q: Are all substitute parts RoHS3 compliant?

A: All substitute parts except 4N36 are RoHS3 compliant. The 4N36 is RoHS non-compliant and REACH affected. For applications requiring environmental compliance certification, select from RoHS3-compliant alternatives.

Q: What inventory levels are available for each substitute?

A: Inventory varies significantly. The 4N36 has the highest availability (100,400 Pcs), while Group B and C parts range from 748 to 1,771 Pcs. The 4N37 has 19,066 Pcs in stock. Verify current inventory status with suppliers before design commitment.

Q: Can MCT2202X be used if CTR variation is acceptable?

A: MCT2202X specifies CTR range of 63% to 125% at 10mA, providing broader tolerance than the 4N37's fixed 100% minimum. This part is suitable only if circuit design accommodates CTR variation across the specified range. Verify output current requirements at minimum CTR (63%) before selection.

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