KA7818E Equivalent & Substitute Parts

Part Overview

The KA7818E is a linear voltage regulator IC from onsemi designed to provide a fixed positive 18V output at 1A current capacity in a TO-220-3 package. This device is classified as obsolete, making equivalent and substitute parts necessary for ongoing design support and component sourcing. The KA7818E serves applications requiring stable 18V regulation with thermal and short-circuit protection in through-hole mounting configurations.

Key Parameters

Parameter	Value
Manufacturer Part Number	KA7818E
Manufacturer	onsemi
Product Status	Obsolete
Output Voltage (Fixed)	18V
Output Current	1A
Input Voltage (Max)	35V
Voltage Dropout (Max)	2V @ 1A (Typ)
Quiescent Current	8 mA
PSRR	69dB (120Hz)
Protection Features	Over Temperature, Short Circuit
Operating Temperature Range	-40°C ~ 125°C
Package / Case	TO-220-3
Mounting Type	Through Hole
Moisture Sensitivity Level	1 (Unlimited)

Substitute Part Grouping Explanation

Substitution for the KA7818E is determined by the following critical parameters:

Fixed output voltage of 18V
Output current capability of 1A or greater
Maximum input voltage of 35V or greater
TO-220-3 package or compatible through-hole package
Over temperature and short circuit protection
Operating temperature range compatibility

Substitute parts are grouped into three categories:

Direct Equivalents (Identical Specifications): Parts with matching output current (1A), identical voltage ratings, and equivalent performance characteristics.

Similar Parts (Reduced Current Output): Parts with 500mA output current, suitable only for applications requiring less than 1A.

Parametric Equivalents (Enhanced Specifications): Parts with higher output current capability (1.5A or 2A), providing superior performance margin while maintaining 18V output and TO-220-3 compatibility.

Parameter Comparison

Part Number	Manufacturer	Product Status	Output Voltage	Output Current	Input Voltage (Max)	Dropout Voltage	Quiescent Current	PSRR (120Hz)	Operating Temp Range	Package
KA7818E	onsemi	Obsolete	18V	1A	35V	2V @ 1A	8 mA	69dB	-40°C ~ 125°C	TO-220-3
MC7818BTG	onsemi	Active	18V	1A	35V	2V @ 1A	8 mA	57dB	-40°C ~ 125°C	TO-220-3
MC7818CTG	onsemi	Active	18V	1A	35V	2V @ 1A	6.5 mA	57dB	0°C ~ 125°C	TO-220-3
MC78M18CTG	onsemi	Obsolete	18V	500mA	35V	—	—	70dB	0°C ~ 125°C	TO-220-3
L7818CV-DG	STMicroelectronics	Obsolete	18V	1.5A	35V	2V @ 1A	8 mA	53dB	0°C ~ 125°C	TO-220-3
L78S18CV	STMicroelectronics	Obsolete	18V	2A	35V	—	8 mA	43dB	0°C ~ 150°C	TO-220-3
MC7818ACTG	onsemi	Obsolete	18V	1A	35V	2V @ 1A	6 mA	57dB	0°C ~ 125°C	TO-220-3
MC78M18BTG	onsemi	Obsolete	18V	500mA	35V	—	—	70dB	-40°C ~ 125°C	TO-220-3
KA7818ETU-ON	onsemi	Active	18V	1A	35V	2V @ 1A	8 mA	69dB	-40°C ~ 125°C	TO-220-3

Engineering Selection Recommendations

Primary Recommendation - KA7818ETU-ON: This onsemi part is a parametric equivalent with active product status. It maintains identical electrical specifications to the KA7818E, including 69dB PSRR, 8mA quiescent current, and -40°C to 125°C operating range. RoHS3 compliance and REACH unaffected status support modern supply chain requirements. Bulk packaging is available with 20,170 units in stock.

Secondary Recommendation - MC7818BTG: An active onsemi product offering 1A output current with identical voltage ratings and dropout characteristics. Operating temperature range matches the original (-40°C to 125°C). ROHS3 compliant with 17,100 units in stock. PSRR is reduced to 57dB compared to the original 69dB.

Alternative for Enhanced Performance - L78S18CV: STMicroelectronics part providing 2A output current, doubling the current capacity while maintaining 18V output and TO-220-3 compatibility. Extended operating temperature range to 150°C. Suitable for applications requiring additional current margin. Product status is obsolete; 2,737 units in stock.

Not Recommended for Direct Substitution - MC78M18CTG and MC78M18BTG: These parts provide only 500mA output current, insufficient for applications designed for 1A operation. Use only if application requirements have been verified to operate below 500mA.

Frequently Asked Questions (FAQ)

Q: Can MC7818BTG directly replace KA7818E? A: Yes. MC7818BTG provides identical 1A output current, 18V fixed output, and -40°C to 125°C operating range. Both are TO-220-3 packages with equivalent dropout voltage and protection features. The primary difference is PSRR (57dB vs. 69dB), which does not affect basic regulation functionality.

Q: What is the difference between KA7818ETU-ON and KA7818E? A: KA7818ETU-ON is the active production equivalent of the obsolete KA7818E. Electrical specifications are identical, including 69dB PSRR, 8mA quiescent current, and -40°C to 125°C range. The primary difference is packaging format (bulk vs. standard) and active product status, ensuring long-term availability.

Q: Can L78S18CV be used as a drop-in replacement? A: L78S18CV is mechanically and electrically compatible in TO-220-3 applications. It provides 2A output current versus the original 1A, offering superior performance margin. However, it is an obsolete product. Use only if enhanced current capacity is beneficial and long-term availability is not critical.

Q: Why should I avoid MC78M18CTG for 1A applications? A: MC78M18CTG is rated for 500mA maximum output current. Using it in a circuit designed for 1A operation will cause the device to operate beyond its rated capacity, resulting in thermal stress, potential shutdown, or component failure.

Q: Are all substitute parts RoHS3 compliant? A: Most substitute parts listed are RoHS3 compliant. KA7818ETU-ON and MC7818BTG explicitly state ROHS3 compliance. Verify compliance status for specific procurement requirements, as some obsolete parts may have different compliance designations.

Q: What is the significance of the TO-220-3 package? A: TO-220-3 is a through-hole package with three leads (input, ground, output). All listed substitutes use this identical package, ensuring mechanical and electrical compatibility without PCB redesign. Mounting and thermal management characteristics remain consistent across all parts.

Q: Can I use a higher current-rated part in a 1A circuit? A: Yes. Parts rated for 1.5A (L7818CV-DG) or 2A (L78S18CV) can be used in 1A applications. The regulator will supply only the current demanded by the load, operating safely within its rated capacity. This approach provides additional thermal margin and design headroom.

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