3C91CTX Optoisolator Equivalent & Substitute Parts

Part Overview

The 3C91CTX is a 1000VDC isolation optoisolator with transistor output in TO-72-4 metal can packaging, manufactured by TT Electronics/Optek Technology. This component is classified as obsolete, which necessitates identification of active equivalent parts for ongoing design support and procurement. The 3C91CTX maintains a single isolation channel with 30-200% current transfer ratio and 30mA maximum output current, suitable for applications requiring galvanic isolation in industrial and control systems.

Key Parameters

Parameter	Value
Manufacturer Part Number	3C91CTX
Manufacturer	TT Electronics/Optek Technology
Category	Optoisolators
Number of Channels	1
Voltage - Isolation	1000VDC
Current Transfer Ratio (Min)	30% @ 10mA
Current Transfer Ratio (Max)	200% @ 10mA
Turn On / Turn Off Time (Typ)	9µs, 6µs (Max)
Output Type	Transistor
Voltage - Output (Max)	50V
Current - Output / Channel	30mA
Voltage - Forward (Vf) (Typ)	1.2V (Max)
Current - DC Forward (If) (Max)	50mA
Vce Saturation (Max)	400mV
Operating Temperature	-55°C ~ 125°C
Mounting Type	Through Hole
Package / Case	TO-206AF, TO-72-4 Metal Can
Product Status	Obsolete
RoHS Status	RoHS non-compliant

Substitute Part Grouping Explanation

Substitution of the 3C91CTX is determined by strict equivalence across the following critical parameters:

Isolation Voltage: 1000VDC minimum
Number of Channels: 1 channel configuration
Output Type: Transistor output
Current Transfer Ratio Range: 30% (Min) to 200% (Max) @ 10mA
Maximum Output Current: 30mA per channel
Switching Speed: Turn-on/turn-off times of 9µs and 6µs (Max)
Output Voltage Rating: 50V maximum
Vce Saturation: 400mV maximum
Operating Temperature Range: -55°C to 125°C
Package Type: TO-72-4 metal can through-hole mounting

The 3C91C is identified as the direct manufacturer-recommended substitute, maintaining identical electrical specifications and package configuration while offering active product status and improved compliance posture.

Parameter Comparison

Parameter	3C91CTX (Main Part)	3C91C (Substitute)	Match Status
Manufacturer	TT Electronics/Optek Technology	TT Electronics/Optek Technology	Identical
Number of Channels	1	1	Identical
Voltage - Isolation	1000VDC	1000VDC	Identical
Current Transfer Ratio (Min)	30% @ 10mA	30% @ 10mA	Identical
Current Transfer Ratio (Max)	200% @ 10mA	200% @ 10mA	Identical
Turn On / Turn Off Time (Typ)	9µs, 6µs (Max)	9µs, 6µs (Max)	Identical
Output Type	Transistor	Transistor	Identical
Voltage - Output (Max)	50V	50V	Identical
Current - Output / Channel	30mA	30mA	Identical
Voltage - Forward (Vf) (Typ)	1.2V (Max)	1.2V (Max)	Identical
Current - DC Forward (If) (Max)	50mA	50mA	Identical
Vce Saturation (Max)	400mV	400mV	Identical
Operating Temperature	-55°C ~ 125°C	-55°C ~ 125°C	Identical
Mounting Type	Through Hole	Through Hole	Identical
Package / Case	TO-206AF, TO-72-4 Metal Can	TO-206AF, TO-72-4 Metal Can	Identical
Product Status	Obsolete	Active	Substitute is Active
RoHS Status	RoHS non-compliant	ROHS3 Compliant	Substitute offers improved compliance

Engineering Selection Recommendations

The 3C91C is the direct equivalent substitute for the 3C91CTX. All electrical and mechanical parameters are identical, ensuring pin-for-pin and functional compatibility. The 3C91C offers two significant advantages over the obsolete 3C91CTX:

Product Status: The 3C91C maintains active product status, ensuring long-term availability and manufacturer support.
Regulatory Compliance: The 3C91C is ROHS3 compliant, whereas the 3C91CTX is RoHS non-compliant. This compliance improvement aligns with current environmental and regulatory requirements for electronic components in most markets.

Both parts share identical isolation voltage (1000VDC), current transfer ratio specifications (30-200% @ 10mA), output current capability (30mA), switching characteristics (9µs turn-on, 6µs turn-off maximum), and TO-72-4 metal can through-hole packaging. No circuit modifications or design changes are required for substitution.

Frequently Asked Questions (FAQ)

Q: Can the 3C91C directly replace the 3C91CTX without circuit modifications?

A: Yes. The 3C91C is electrically and mechanically identical to the 3C91CTX. All specifications including isolation voltage, current transfer ratio, output current, switching speed, and package configuration are equivalent. Direct substitution is possible without design changes.

Q: What is the primary reason to substitute the 3C91CTX?

A: The 3C91CTX is classified as obsolete. The 3C91C is the manufacturer-recommended active equivalent, ensuring continued availability and long-term supply chain reliability.

Q: Are there compliance differences between the 3C91CTX and 3C91C?

A: Yes. The 3C91C is ROHS3 compliant, while the 3C91CTX is RoHS non-compliant. For applications subject to RoHS regulations or customer requirements, the 3C91C is the appropriate selection.

Q: Is the TO-72-4 metal can package identical between both parts?

A: Yes. Both the 3C91CTX and 3C91C use the TO-206AF / TO-72-4 metal can package with through-hole mounting. Pin configuration and physical dimensions are identical.

Q: What are the key electrical parameters that define substitution eligibility?

A: Substitution is based on matching: 1000VDC isolation voltage, single-channel configuration, 30-200% current transfer ratio @ 10mA, 30mA maximum output current, 50V maximum output voltage, 400mV maximum Vce saturation, and -55°C to 125°C operating temperature range.

Q: Is the 3C91C the only available substitute?

A: Based on the provided data, the 3C91C is the manufacturer-recommended substitute. Both parts are from TT Electronics/Optek Technology and share identical specifications.

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