MC7818ACT Linear Voltage Regulator - Equivalent & Substitute Parts

Part Overview

The MC7818ACT is a linear voltage regulator IC from onsemi, classified as a Power Management (PMIC) component. It delivers a fixed positive 18V output at 1A maximum current in a TO-220-3 package configuration. The device is currently listed as obsolete, making equivalent and substitute parts necessary for ongoing design support and component procurement.

Substiute Parts

MC7818ACT

onsemiIn Stock: 924MC7818ACT Datasheet

Current PartRFQ

MC7818CTG

onsemiIn Stock: 1503MC7818CTG Datasheet

Parametric EquivalentRFQ

MC7818ACTG

onsemiIn Stock: 1773MC7818ACTG Datasheet

DirectRFQ

L78S18CV

STMicroelectronicsIn Stock: 2795L78S18CV Datasheet

SimilarRFQ

Key Parameters

Substitute Part Grouping Explanation

Substitution for the MC7818ACT is determined by the following critical parameters:

• Output Voltage: 18V fixed (non-adjustable)
• Output Current Capability: Minimum 1A
• Package Type: TO-220-3 (mechanical and thermal compatibility)
• Input Voltage Range: Maximum 35V
• Output Configuration: Positive fixed regulator
• Mounting Type: Through Hole

Substitute parts are grouped into two categories:

Parametric Equivalent (Direct Replacement): Parts with identical electrical specifications and package configuration, differing only in product status or minor quiescent current variations within acceptable tolerances.

Direct Manufacturer Equivalent: Parts from the same manufacturer with identical specifications but different packaging or product status designation.

Similar Substitute: Parts with higher current capability or extended temperature range that maintain electrical compatibility while offering enhanced performance characteristics.

Parameter Comparison

Engineering Selection Recommendations

MC7818CTG is the primary recommended substitute. It is manufactured by onsemi with identical electrical specifications to the MC7818ACT, maintains the same TO-220-3 package configuration, and carries Active product status. The MC7818CTG is ROHS3 compliant, addressing regulatory requirements that the obsolete MC7818ACT does not meet. Quiescent current is marginally higher at 6.5 mA compared to 6 mA, which is within acceptable tolerance for most applications.

MC7818ACTG provides an alternative from onsemi with identical electrical performance to the MC7818ACT. However, it retains Obsolete product status and does not offer the regulatory advantage of the MC7818CTG. This part is suitable only when existing inventory must be maintained or when RoHS compliance is not a design requirement.

L78S18CV from STMicroelectronics is a similar substitute offering higher output current capability (2A versus 1A) and extended operating temperature range (0°C ~ 150°C). The TO-220-3 package remains compatible. This part includes Over Current protection in addition to Over Temperature and Short Circuit protection. PSRR is reduced to 43dB compared to 57dB in the onsemi variants. The L78S18CV is suitable for applications requiring higher current delivery or extended temperature operation, provided the reduced PSRR is acceptable for the intended application.

Frequently Asked Questions (FAQ)

Q: Can MC7818CTG directly replace MC7818ACT in existing designs?

A: Yes. The MC7818CTG is electrically and mechanically identical to the MC7818ACT. Both deliver 18V at 1A maximum output current in the same TO-220-3 package. The primary difference is product status (Active versus Obsolete) and RoHS compliance. No circuit modifications are required.

Q: What is the significance of the quiescent current difference between MC7818ACT (6 mA) and MC7818CTG (6.5 mA)?

A: The 0.5 mA difference is negligible for most applications. Quiescent current represents the current drawn by the regulator itself when no load is connected. In typical designs, this represents less than 1% of total system current and does not affect circuit functionality or thermal performance.

Q: Why does L78S18CV have lower PSRR (43dB) compared to MC7818ACT (57dB)?

A: PSRR (Power Supply Rejection Ratio) measures the regulator's ability to reject input voltage ripple. The 14dB difference indicates that L78S18CV is less effective at filtering input noise. For noise-sensitive applications, MC7818CTG is the preferred choice. For general-purpose applications, L78S18CV remains acceptable.

Q: Is L78S18CV suitable as a drop-in replacement for MC7818ACT?

A: L78S18CV is mechanically compatible (TO-220-3 package) and electrically compatible for applications requiring up to 1A output current. However, it is not a true drop-in replacement due to reduced PSRR and different quiescent current. Use L78S18CV only when higher current capability (2A) or extended temperature range (0°C ~ 150°C) is required for the application.

Q: What does RoHS compliance mean for component selection?

A: RoHS (Restriction of Hazardous Substances) compliance indicates the part meets environmental regulations restricting lead and other hazardous materials. MC7818CTG and MC7818ACTG are ROHS3 compliant, while MC7818ACT is not. For new designs or applications subject to environmental regulations, ROHS3 compliant parts are required.

Q: Can I use MC7818ACTG instead of MC7818CTG?

A: Both parts are electrically identical. MC7818ACTG is suitable if existing inventory is available or if RoHS compliance is not a requirement. However, MC7818CTG is preferred for new designs due to Active product status and ROHS3 compliance, ensuring long-term availability and regulatory alignment.

Q: What is the difference between TO-220 and TO-220-3 package designations?

A: TO-220-3 specifies a three-pin TO-220 package configuration (Input, Ground, Output). All listed parts use this identical package, ensuring mechanical and thermal compatibility in PCB layouts and heat sink mounting.