LM79M12CT Equivalent & Substitute Parts

Part Overview

The LM79M12CT is a linear voltage regulator IC manufactured by Texas Instruments, designed to provide a fixed negative 12V 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 procurement.

The LM79M12CT serves applications requiring negative voltage regulation with moderate current capacity. Substitute parts must maintain electrical compatibility across output voltage, current rating, input voltage tolerance, and thermal characteristics while accommodating modern component availability and compliance requirements.

Key Parameters

Parameter	LM79M12CT
Output Voltage (Fixed)	-12V
Output Current	500mA
Input Voltage (Max)	-35V
Voltage Dropout (Max)	1.1V @ 500mA
Quiescent Current	1.5 mA
PSRR	70dB (120Hz)
Protection Features	Over Temperature, Short Circuit
Operating Temperature	0°C ~ 125°C
Package	TO-220-3
Product Status	Obsolete

Substitute Part Grouping Explanation

Substitution for the LM79M12CT is determined by the following critical parameters:

Output Voltage: Must be fixed at -12V
Output Current Capacity: Minimum 500mA required for direct replacement; higher ratings (1A, 1.5A) are acceptable for applications with lower current demands
Input Voltage Range: Maximum -35V input tolerance required
Package Type: TO-220-3 through-hole mounting
Protection Features: Over temperature and short circuit protection required
Operating Temperature Range: 0°C to 125°C minimum

Substitute parts are grouped into two categories based on output current capacity:

Category 1: 500mA Output Current (Direct Equivalents)

MC79M12BTG (onsemi)

Category 2: Higher Current Output (1A and 1.5A Upgrades)

MC7912ACTG, MC7912BTG, MC7912CTG (onsemi, 1A output)
L7912ACV, L7912ACV-DG, L7912CV, L7912CV-DG (STMicroelectronics, 1.5A output)

Parameter Comparison

Parameter	LM79M12CT	MC79M12BTG	MC7912ACTG	MC7912BTG	MC7912CTG	L7912ACV	L7912ACV-DG	L7912CV	L7912CV-DG
Output Voltage	-12V	-12V	-12V	-12V	-12V	-12V	-12V	-12V	-12V
Output Current	500mA	500mA	1A	1A	1A	1.5A	1.5A	1.5A	1.5A
Input Voltage (Max)	-35V	-35V	-35V	-35V	-35V	-35V	-35V	-35V	-35V
Voltage Dropout (Max)	1.1V @ 500mA	1.1V @ 500mA	1.3V @ 1A	1.3V @ 1A	1.3V @ 1A	1.1V @ 1A	1.1V @ 1A	1.1V @ 1A	1.1V @ 1A
Quiescent Current	1.5 mA	Not specified	Not specified	Not specified	Not specified	3 mA	3 mA	3 mA	3 mA
PSRR	70dB (120Hz)	60dB (120Hz)	61dB (120Hz)	61dB (120Hz)	61dB (120Hz)	60dB (120Hz)	60dB (120Hz)	60dB (120Hz)	60dB (120Hz)
Protection Features	Over Temperature, Short Circuit	Over Current, Over Temperature	Over Current, Over Temperature	Over Current, Over Temperature	Over Current, Over Temperature	Over Temperature, Short Circuit	Over Temperature, Short Circuit	Over Temperature, Short Circuit	Over Temperature, Short Circuit
Operating Temperature	0°C ~ 125°C	-40°C ~ 125°C	0°C ~ 125°C	-40°C ~ 125°C	0°C ~ 125°C	0°C ~ 125°C	0°C ~ 125°C	0°C ~ 125°C	0°C ~ 125°C
Package	TO-220-3	TO-220-3	TO-220-3	TO-220-3	TO-220-3	TO-220-3	TO-220-3	TO-220-3	TO-220-3
Product Status	Obsolete	Active	Active	Active	Active	Active	Obsolete	Active	Active
RoHS Status	Non-compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant

Engineering Selection Recommendations

For Direct 500mA Replacement: MC79M12BTG is the primary equivalent, offering identical 500mA output current and matching electrical specifications. This part is manufactured by onsemi, carries active product status, and is ROHS3 compliant. The extended operating temperature range (-40°C to 125°C) provides additional thermal margin compared to the original LM79M12CT.

For Higher Current Applications (1A Output): MC7912ACTG, MC7912BTG, and MC7912CTG are suitable when application requirements permit 1A output current. All three are onsemi products with active status and ROHS3 compliance. MC7912BTG offers the widest operating temperature range (-40°C to 125°C). These parts feature over-current protection in addition to over-temperature protection.

For Higher Current Applications (1.5A Output): L7912CV-DG and L7912CV are STMicroelectronics products with the highest current capacity (1.5A) and active product status. Both are ROHS3 compliant. L7912CV-DG has the largest inventory availability (158,850 units). These parts provide superior current headroom for applications with variable or future current demands.

All substitute parts maintain the required -12V fixed output voltage, -35V maximum input voltage, TO-220-3 package compatibility, and operating temperature range of 0°C to 125°C or better. All substitute parts are ROHS3 compliant, addressing the non-compliance status of the obsolete LM79M12CT.

Frequently Asked Questions (FAQ)

Q: Can I use a 1A or 1.5A rated regulator in place of the 500mA LM79M12CT?

A: Yes. Higher current-rated regulators are electrically compatible substitutes. The output voltage (-12V), input voltage tolerance (-35V max), and package (TO-220-3) remain identical. The higher current rating does not affect operation in circuits designed for 500mA or less. No circuit modifications are required.

Q: What is the difference between MC79M12BTG and MC7912ACTG?

A: MC79M12BTG provides 500mA output current, matching the original LM79M12CT specification. MC7912ACTG provides 1A output current. Both use TO-220-3 packages and maintain -12V output voltage. MC7912ACTG is suitable if your application requires higher current capacity or future design margin.

Q: Are STMicroelectronics L7912 parts compatible with onsemi MC7912 parts?

A: Yes. Both manufacturers produce -12V negative regulators in TO-220-3 packages with identical output voltage, input voltage range, and protection features. They are electrically interchangeable. The primary differences are output current capacity (1A for onsemi MC7912, 1.5A for STMicroelectronics L7912) and quiescent current specifications.

Q: Why do some substitute parts have higher quiescent current (3mA vs 1.5mA)?

A: Quiescent current represents the regulator's internal power consumption when no load is connected. The STMicroelectronics L7912 series specifies 3mA quiescent current compared to the LM79M12CT's 1.5mA. This difference is acceptable for most applications and does not affect circuit functionality. For battery-powered or ultra-low-power applications, verify quiescent current specifications against your design requirements.

Q: What does ROHS3 compliance mean for my design?

A: ROHS3 compliance indicates the part meets Restriction of Hazardous Substances Directive requirements, restricting lead and other hazardous materials. The original LM79M12CT is non-compliant. All substitute parts listed are ROHS3 compliant, supporting modern manufacturing and environmental standards.

Q: Can I substitute L7912ACV-DG if it is listed as obsolete?

A: L7912ACV-DG is obsolete but remains available in inventory (5,400 units). For new designs, L7912CV-DG is the recommended active alternative with identical electrical specifications and superior availability (158,850 units). For legacy system repairs, L7912ACV-DG remains a valid substitute if inventory is accessible.

Q: Do all substitute parts fit the same PCB footprint?

A: Yes. All substitute parts use the TO-220-3 package with identical pin configuration and mechanical dimensions. No PCB layout modifications are required for any listed substitute.

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