LM78M15CT Linear Voltage Regulator Equivalent & Substitute Parts

Part Overview

The LM78M15CT is a linear voltage regulator IC manufactured by onsemi, designed to provide a fixed positive 15V 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 and production continuity. The LM78M15CT serves applications requiring regulated 15V power from higher input voltages up to 35V, with integrated over-temperature and short-circuit protection.

Key Parameters

Parameter	Value
Output Voltage (Fixed)	15V
Output Current	500mA
Input Voltage (Max)	35V
Voltage Dropout (Max)	2V @ 500mA (Typ)
Quiescent Current (Iq)	6 mA
PSRR	70dB (120Hz)
Operating Temperature Range	0°C ~ 125°C
Package / Case	TO-220-3
Protection Features	Over Temperature, Short Circuit
Product Status	Obsolete

Substitute Part Grouping Explanation

Substitution of the LM78M15CT is determined by the following critical parameters:

Output Voltage: All substitutes must provide fixed 15V output
Package / Case: All substitutes must use TO-220-3 package for mechanical and thermal compatibility
Output Configuration: All substitutes must be positive output regulators
Protection Features: All substitutes must include over-temperature and short-circuit protection
Input Voltage Rating: All substitutes must support maximum input voltage of 32V or higher

Substitute parts are grouped into two categories:

Parametric Equivalent (500mA Output Current): MC78M15CTG matches the original 500mA output current specification, providing direct functional replacement with identical current rating.

Higher Current Alternatives (1A or 1.5A Output Current): MC7815ACTG, MC7815BTG, MC7815CTG, AS7815AT-E1, L7815ABV, L7815ACV, L7815ACV-DG, L7815CV, and L7815CV-DG provide higher output current ratings. These are suitable for applications where the original 500mA specification can accommodate higher current capability without design modification.

Parameter Comparison

Part Number	Manufacturer	Output Current	Input Voltage (Max)	Voltage Dropout (Max)	Quiescent Current (Iq)	PSRR (120Hz)	Operating Temperature	Product Status	RoHS Status
LM78M15CT	onsemi	500mA	35V	2V @ 500mA	6 mA	70dB	0°C ~ 125°C	Obsolete	Not Specified
MC78M15CTG	onsemi	500mA	35V	Not Specified	Not Specified	70dB	0°C ~ 125°C	Active	ROHS3 Compliant
MC7815ACTG	onsemi	1A	35V	2V @ 1A	6 mA	80dB	0°C ~ 125°C	Active	ROHS3 Compliant
MC7815BTG	onsemi	1A	35V	2V @ 1A	8 mA	58dB	-40°C ~ 125°C	Active	ROHS3 Compliant
MC7815CTG	onsemi	1A	35V	2V @ 1A	6.5 mA	58dB	0°C ~ 125°C	Active	ROHS3 Compliant
AS7815AT-E1	Diodes Incorporated	1A	32V	2V @ 1A	6 mA	58dB	-40°C ~ 125°C	Active	ROHS3 Compliant
L7815ABV	STMicroelectronics	1.5A	35V	2V @ 1A	6 mA	58dB	-40°C ~ 125°C	Active	ROHS3 Compliant
L7815ACV	STMicroelectronics	1.5A	35V	2V @ 1A	6 mA	58dB	0°C ~ 125°C	Active	ROHS3 Compliant
L7815ACV-DG	STMicroelectronics	1.5A	35V	2V @ 1A	6 mA	58dB	0°C ~ 125°C	Active	ROHS3 Compliant
L7815CV	STMicroelectronics	1.5A	35V	2V @ 1A	8 mA	54dB	0°C ~ 125°C	Active	ROHS3 Compliant
L7815CV-DG	STMicroelectronics	1.5A	35V	2V @ 1A	8 mA	54dB	0°C ~ 125°C	Active	ROHS3 Compliant

Engineering Selection Recommendations

Primary Recommendation: MC78M15CTG (onsemi) is the direct parametric equivalent, providing identical 500mA output current and 70dB PSRR performance. This part is active and ROHS3 compliant, offering the closest functional match to the obsolete LM78M15CT.

Alternative for Extended Temperature Range: AS7815AT-E1 (Diodes Incorporated) supports operating temperatures from -40°C to 125°C, compared to the original 0°C to 125°C range. This part is suitable for applications requiring wider temperature operation while maintaining 1A output capability.

Higher Current Alternatives: MC7815ACTG, MC7815CTG, L7815ABV, L7815ACV, L7815ACV-DG, L7815CV, and L7815CV-DG provide 1A or 1.5A output current ratings. These parts are suitable for designs where increased current headroom is acceptable and beneficial for thermal performance.

Extended Temperature Variants: MC7815BTG and L7815ABV support -40°C to 125°C operating range, suitable for industrial or automotive applications requiring wider temperature specifications.

All recommended substitutes are ROHS3 compliant and carry active product status, ensuring long-term availability and supply chain stability.

Frequently Asked Questions (FAQ)

Q: Can MC78M15CTG directly replace LM78M15CT without circuit modification?

A: Yes. MC78M15CTG is a parametric equivalent with matching 500mA output current, 15V fixed output, 35V maximum input voltage, and TO-220-3 package. No circuit modification is required.

Q: What is the difference between 500mA and 1A output current variants?

A: The LM78M15CT and MC78M15CTG are rated for 500mA maximum output current. MC7815ACTG, MC7815BTG, and MC7815CTG are rated for 1A. The 1A variants can supply higher load current and typically offer better thermal performance due to lower junction temperature at equivalent power dissipation. Selection depends on application current requirements.

Q: Are all substitute parts available in TO-220-3 package?

A: Yes. All listed substitute parts use TO-220-3 package, ensuring mechanical and thermal compatibility with the original LM78M15CT footprint.

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

A: PSRR measures the regulator's ability to reject input voltage ripple and noise. The LM78M15CT and MC78M15CTG both provide 70dB PSRR at 120Hz. Higher PSRR values indicate better noise rejection. Most 1A variants provide 58dB PSRR, which is acceptable for most applications but represents a trade-off for increased current capability.

Q: Which substitute offers the widest operating temperature range?

A: AS7815AT-E1, MC7815BTG, and L7815ABV support -40°C to 125°C operating range, compared to the original 0°C to 125°C specification. These parts are suitable for industrial and automotive applications.

Q: Are all substitutes ROHS3 compliant?

A: Yes. All active substitute parts listed are ROHS3 compliant. The original LM78M15CT does not specify RoHS status due to its obsolete classification.

Q: What is the difference between L7815ACV and L7815ACV-DG?

A: Both parts are manufactured by STMicroelectronics with identical electrical specifications (1.5A output, 15V fixed output, 35V maximum input). The "-DG" suffix indicates a different packaging or distribution format. Electrical performance and TO-220-3 package compatibility are equivalent.

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