MC7818ECT Equivalent & Substitute Parts

Part Overview

The MC7818ECT is a linear voltage regulator IC from onsemi designed to provide a fixed positive 18V output at 1A in a TO-220-3 package. This part is classified as obsolete, making equivalent and substitute parts necessary for ongoing design support and procurement. The MC7818ECT serves applications requiring stable 18V regulation with thermal and short-circuit protection in through-hole mounting configurations.

Key Parameters

Parameter	Value
Manufacturer	onsemi
Output Voltage (Fixed)	18V
Output Current	1A
Input Voltage (Max)	35V
Voltage Dropout (Typ)	2V @ 1A
Quiescent Current	8 mA
PSRR	69dB (120Hz)
Protection Features	Over Temperature, Short Circuit
Operating Temperature	0°C ~ 125°C
Package	TO-220-3
Mounting Type	Through Hole
Product Status	Obsolete

Substitute Part Grouping Explanation

Substitution for the MC7818ECT 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
Positive output configuration
Over temperature and short circuit protection

Substitute parts are grouped into two categories:

Direct Equivalents (Same Output Current): Parts with 1A output current matching the MC7818ECT specification, enabling pin-for-pin or functional replacement without circuit modification.

Higher Current Alternatives: Parts with output current ratings exceeding 1A, suitable for applications where additional current headroom is beneficial while maintaining the same voltage regulation and protection characteristics.

Parameter Comparison

Part Number	Manufacturer	Output Voltage	Output Current	Input Voltage (Max)	Dropout Voltage	Quiescent Current	PSRR (120Hz)	Operating Temp	Product Status	Package
MC7818ECT	onsemi	18V	1A	35V	2V @ 1A	8 mA	69dB	0°C ~ 125°C	Obsolete	TO-220-3
MC7818BTG	onsemi	18V	1A	35V	2V @ 1A	8 mA	57dB	-40°C ~ 125°C	Active	TO-220-3
MC7818CTG	onsemi	18V	1A	35V	2V @ 1A	6.5 mA	57dB	0°C ~ 125°C	Active	TO-220-3
MC7818ACTG	onsemi	18V	1A	35V	2V @ 1A	6 mA	57dB	0°C ~ 125°C	Obsolete	TO-220-3
MC78M18CTG	onsemi	18V	500mA	35V	—	—	70dB	0°C ~ 125°C	Obsolete	TO-220-3
MC78M18BTG	onsemi	18V	500mA	35V	—	—	70dB	-40°C ~ 125°C	Obsolete	TO-220-3
L7818CV-DG	STMicroelectronics	18V	1.5A	35V	2V @ 1A	8 mA	53dB	0°C ~ 125°C	Obsolete	TO-220-3
L78S18CV	STMicroelectronics	18V	2A	35V	—	8 mA	43dB	0°C ~ 150°C	Obsolete	TO-220-3

Engineering Selection Recommendations

Primary Recommendation: MC7818BTG (onsemi)

MC7818BTG is the preferred direct substitute for MC7818ECT. Both parts share identical electrical specifications (18V output, 1A current, 35V maximum input, 2V dropout voltage) and package configuration. MC7818BTG holds active product status, ensuring long-term availability and supply chain stability. The extended operating temperature range (-40°C to 125°C) provides additional environmental flexibility compared to the MC7818ECT specification (0°C to 125°C). RoHS3 compliance and REACH unaffected status meet modern regulatory requirements.

Secondary Recommendation: MC7818CTG (onsemi)

MC7818CTG is a parametric equivalent with active product status. It maintains the same 18V output, 1A current, and 35V input specifications. The quiescent current is reduced to 6.5 mA compared to 8 mA in the original part, offering improved power efficiency. This part is suitable for applications where lower standby power consumption is beneficial.

Higher Current Alternative: L7818CV-DG (STMicroelectronics)

L7818CV-DG provides 1.5A output current in the same TO-220-3 package, offering 50% additional current capacity while maintaining 18V regulation and 35V maximum input voltage. This part is appropriate for designs requiring current margin or future load expansion. Operating temperature range matches the MC7818ECT specification (0°C to 125°C).

Maximum Current Alternative: L78S18CV (STMicroelectronics)

L78S18CV delivers 2A output current, doubling the original part's capacity. It maintains 18V output and 35V maximum input specifications. The extended operating temperature range (0°C to 150°C) supports high-temperature applications. This part is suitable for designs with significant current requirements or thermal margin needs.

Not Recommended: MC78M18CTG and MC78M18BTG

These 500mA parts provide insufficient output current for applications designed around the 1A MC7818ECT specification and should not be used as direct substitutes.

Frequently Asked Questions (FAQ)

Q: Can MC7818BTG replace MC7818ECT directly?

A: Yes. MC7818BTG is a direct functional replacement. Both parts provide 18V fixed output at 1A with identical electrical characteristics and TO-220-3 packaging. MC7818BTG is actively manufactured, making it the recommended substitute for obsolete MC7818ECT applications.

Q: What is the difference between MC7818CTG and MC7818BTG?

A: Both are 18V, 1A regulators in TO-220-3 packages with active product status. MC7818CTG has lower quiescent current (6.5 mA vs. 8 mA) and operates over 0°C to 125°C. MC7818BTG operates over the extended range of -40°C to 125°C. Select MC7818BTG for wider temperature applications; select MC7818CTG for lower power consumption requirements.

Q: Can I use L78S18CV (2A) instead of MC7818ECT (1A)?

A: Yes, L78S18CV is electrically compatible and provides higher current capacity. The 2A rating ensures adequate headroom for 1A applications. However, verify that your circuit board layout and thermal management accommodate the potentially different package variant. Both use TO-220-3 packages.

Q: Why are MC78M18CTG and MC78M18BTG not suitable substitutes?

A: These parts are rated for 500mA output current, which is insufficient for applications designed around the 1A MC7818ECT specification. Using an undersized regulator may cause voltage regulation failure under full load conditions.

Q: What is the significance of the PSRR (Power Supply Rejection Ratio) differences?

A: PSRR indicates how effectively the regulator rejects input voltage ripple. The MC7818ECT has 69dB PSRR, while most active substitutes (MC7818BTG, MC7818CTG) have 57dB. For noise-sensitive applications, verify that the lower PSRR of substitute parts meets your system requirements. L78S18CV has 43dB PSRR and should be evaluated for high-noise environments.

Q: Are all substitute parts RoHS compliant?

A: MC7818BTG and MC7818CTG are explicitly RoHS3 compliant. L7818CV-DG and L78S18CV are also RoHS3 compliant. All parts listed are REACH unaffected. Verify compliance documentation with your supplier for specific procurement batches.

Q: Can I use these regulators in applications requiring -40°C operation?

A: MC7818BTG and MC78M18BTG support -40°C to 125°C operation. MC7818ECT, MC7818CTG, MC7818ACTG, L7818CV-DG, and L78S18CV are rated 0°C to 125°C. Select MC7818BTG for low-temperature applications below 0°C.

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