LM78M18CT Linear Voltage Regulator Equivalent & Substitute Parts

Part Overview

The LM78M18CT is a linear voltage regulator IC manufactured by onsemi, designed to provide a fixed positive 18V output at 500mA in a TO-220-3 package. This device is classified as obsolete, making equivalent and substitute parts necessary for ongoing design support, maintenance, and production continuity. The LM78M18CT serves applications requiring stable 18V regulation with thermal and short-circuit protection in through-hole mounting configurations.

Substiute Parts

LM78M18CT

onsemiIn Stock: 2214LM78M18CT Datasheet

Current PartRFQ

MC78M18CTG

onsemiIn Stock: 3179MC78M18CTG Datasheet

Parametric EquivalentRFQ

L7818CV-DG

STMicroelectronicsIn Stock: 65494L7818CV-DG Datasheet

SimilarRFQ

Key Parameters

Substitute Part Grouping Explanation

Substitute parts for the LM78M18CT are identified based on strict electrical and mechanical parameter alignment. The primary substitution criteria are:

Critical Parameters for Substitution:

• Fixed output voltage of 18V
• Positive output configuration
• TO-220-3 package with through-hole mounting
• Maximum input voltage of 35V
• Over temperature and short circuit protection
• Operating temperature range 0°C ~ 125°C

Substitution Categories:

Parametric Equivalent: MC78M18CTG maintains identical electrical specifications including 500mA output current, 18V fixed output, 70dB PSRR, and equivalent protection features. The primary difference is packaging format (Tube vs. standard), with both devices meeting the same functional requirements.

Similar Substitute: L7818CV-DG provides higher output current capability (1.5A vs. 500mA) while maintaining the same 18V fixed output voltage, 35V maximum input, TO-220-3 package, and protection features. This part is suitable for applications requiring higher current capacity within the same voltage regulation framework.

Parameter Comparison

Engineering Selection Recommendations

MC78M18CTG Selection Criteria: Select MC78M18CTG when direct parametric equivalence is required. This part maintains identical output current (500mA), PSRR (70dB), and quiescent current specifications as the LM78M18CT. Both devices are obsolete; however, MC78M18CTG offers ROHS3 compliance certification, providing regulatory advantage for new designs or production batches requiring environmental compliance documentation.

L7818CV-DG Selection Criteria: Select L7818CV-DG when the application requires higher output current capacity (1.5A) while maintaining 18V fixed output regulation. This part is suitable for designs where the original 500mA specification is insufficient. The L7818CV-DG is ROHS3 compliant and provides equivalent thermal and short-circuit protection. Note that PSRR is reduced to 53dB compared to the LM78M18CT's 70dB, and quiescent current increases to 8mA. These differences are acceptable in applications where current capacity is the limiting factor.

All three parts share identical package geometry (TO-220-3), maximum input voltage (35V), operating temperature range (0°C ~ 125°C), and protection features, ensuring mechanical and thermal compatibility in existing PCB designs.

Frequently Asked Questions (FAQ)

Q: Can MC78M18CTG be used as a direct drop-in replacement for LM78M18CT? A: Yes. MC78M18CTG is a parametric equivalent with identical electrical specifications (18V output, 500mA current, 70dB PSRR) and identical TO-220-3 package geometry. No circuit modifications are required.

Q: When should L7818CV-DG be selected instead of MC78M18CTG? A: L7818CV-DG should be selected when the application requires output current exceeding 500mA, up to 1.5A. If the circuit is designed for 500mA operation, MC78M18CTG is the appropriate choice. L7818CV-DG is suitable for higher-current applications within the same 18V regulation framework.

Q: Are all three parts compatible with existing PCB designs for LM78M18CT? A: Yes, all three parts use identical TO-220-3 package geometry and pin configuration, ensuring mechanical compatibility with existing through-hole PCB layouts. No PCB modifications are necessary.

Q: What is the significance of PSRR differences between these parts? A: PSRR (Power Supply Rejection Ratio) measures the regulator's ability to reject input voltage ripple. LM78M18CT and MC78M18CTG both provide 70dB PSRR, while L7818CV-DG provides 53dB. For applications sensitive to input ripple, LM78M18CT or MC78M18CTG are preferred. For general-purpose 18V regulation, the 53dB PSRR of L7818CV-DG is typically sufficient.

Q: Do all substitute parts provide the same protection features? A: Yes. All three parts include over temperature and short circuit protection, ensuring equivalent thermal and fault-condition safety.

Q: What is the impact of quiescent current differences? A: LM78M18CT and MC78M18CTG draw 6mA quiescent current, while L7818CV-DG draws 8mA. In battery-powered or low-power standby applications, this 2mA difference may be significant. For line-powered applications, this difference is negligible.

Q: Are RoHS compliance certifications available for all parts? A: MC78M18CTG and L7818CV-DG are both ROHS3 compliant. RoHS status for LM78M18CT is not specified. For designs requiring RoHS compliance documentation, MC78M18CTG or L7818CV-DG are recommended.