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LM78S40CN
Texas Instruments
IC REG BUCK BST ADJ 1.5A 16DIP
7151 Pcs New Original In Stock
Buck, Boost Switching Regulator IC Positive or Negative Adjustable 1.25V 1 Output 1.5A (Switch) 16-DIP (0.300", 7.62mm)
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5.0 / 5.0
- (462 Ratings)
LM78S40CN
Product Overview
1339251
DiGi Electronics Part Number
LM78S40CN-DGManufacturer
Texas Instruments
LM78S40CN
Description
IC REG BUCK BST ADJ 1.5A 16DIPInventory
7151 Pcs New Original In Stock
Buck, Boost Switching Regulator IC Positive or Negative Adjustable 1.25V 1 Output 1.5A (Switch) 16-DIP (0.300", 7.62mm)
Quantity
Minimum 1
Minimum 1
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LM78S40CN Technical Specifications
Category
Power Management (PMIC), Voltage Regulators - DC DC Switching Regulators
Packaging
-
Series
-
Product Status
Obsolete
Function
Step-Up, Step-Down
Output Configuration
Positive or Negative
Topology
Buck, Boost
Output Type
Adjustable
Number of Outputs
1
Voltage - Input (Min)
2.5V
Voltage - Input (Max)
40V
Voltage - Output (Min/Fixed)
1.25V
Voltage - Output (Max)
40V (Switch)
Current - Output
1.5A (Switch)
Frequency - Switching
100Hz ~ 100kHz
Synchronous Rectifier
No
Operating Temperature
0°C ~ 70°C (TA)
Mounting Type
Through Hole
Package / Case
16-DIP (0.300", 7.62mm)
Supplier Device Package
16-PDIP
Base Product Number
LM78S40
Datasheet & Documents
HTML Datasheet
LM78S40CN-DG
Environmental & Export Classification
RoHS Status
RoHS non-compliant
Moisture Sensitivity Level (MSL)
1 (Unlimited)
REACH Status
REACH Unaffected
ECCN
EAR99
HTSUS
8542.39.0001
Additional Information
Standard Package
25
Alternative Parts
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MANUFACTURER
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SUBSTITUTE TYPE
Reviews
5.0/5.0-(Show up to 5 Ratings)
de desembre 02, 2025
Ich bin begeistert von der prompte Versandabwicklung und der freundlichen Beratung.
de desembre 02, 2025
Ich konnte meine Bestellung einfach und schnell aufgeben, und die Versandabwicklung war blitzschnell.
de desembre 02, 2025
Auf meine Bestellung wurde blitzschnell reagiert; großartiger Service!
de desembre 02, 2025
Der schnelle Versand hat meinen Einkauf bei DiGi Electronics sehr angenehm gemacht. Die Produkte sehen aus wie neu, sogar nach Monaten.
de desembre 02, 2025
DiGi Electronicsのウェブサイトはとても見やすくて、必要な情報を素早く見つけられました。使い勝手が良かったです。
de desembre 02, 2025
Their diverse range of solutions caters to both individual and business needs.
de desembre 02, 2025
Their proactive customer service makes a real difference in my experience.
de desembre 02, 2025
Shipping was incredibly fast; I appreciated the timely delivery.
de desembre 02, 2025
Excellent support and timely delivery—made my first purchase a pleasure.
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Frequently Asked Questions (FAQ)
Can I use the LM78S40CN for a wide-input industrial power supply design where VIN fluctuates between 3V and 36V, and what design risks should I consider with this obsolete part?
Yes, the LM78S40CN supports 2.5V to 40V input, making it suitable for fluctuating industrial supplies. However, since it’s obsolete and marked RoHS non-compliant, long-term supply and compliance are risks. Designers must secure lifetime buys or plan early migration. Ensure external components (inductor, diode) are rated for worst-case stress at high VIN, and verify thermal performance without synchronous rectification, which increases losses at higher loads. Use conservative derating on the 1.5A switch current limit to avoid thermal shutdown in continuous heavy loads.
How do I replace the obsolete LM78S40CN with a modern, drop-in compatible switching regulator without redesigning the entire power stage?
The LM78S40CN has no direct modern pin-compatible replacement due to its legacy 16-DIP package and non-synchronous topology. The closest functional alternatives are adjustable buck-boost regulators like the TI LM5118 or Analog Devices LT3791, but they require PCB redesign. For minimal change, consider using the LM78S40CN/NOPB if available in limited stock, but expect higher cost and supply risk. Evaluate redesigning with a modern synchronous controller in a TSSOP or SOIC package with better efficiency and thermal performance.
What are the key reliability concerns when using the LM78S40CN in a high-temperature environment near its 70°C max operating temperature?
The LM78S40CN has a TA limit of 70°C (not TJ), so ambient temperature must include margin for self-heating. Without synchronous rectification, the external switching transistor and power diode dissipate significant heat—especially at high input/output differentials or switching frequencies near 100kHz. Use thermal vias or heatsinking for external pass elements, limit duty cycles under heavy load, and avoid confined enclosures. Operating near 70°C ambient risks thermal runaway; derate output current by at least 30% and monitor case temperature in prototype testing.
Is the LM78S40CN suitable for generating a stable negative output voltage from a single positive supply, and what are the key layout challenges?
Yes, the LM78S40CN can generate negative outputs using a buck-boost topology, which is useful for legacy dual-rail designs. The main challenge is proper grounding: separate power and signal grounds must be joined at a single point near the IC to avoid noise coupling. Pay close attention to the feedback divider return, which connects to the negative output, not system ground. Use a low-ESR output capacitor and minimize loop area for the inductor-switch-diode path to reduce EMI and voltage spikes on the 1.5A switch node.
How does the LM78S40CN compare to the MC34063A in terms of efficiency, design complexity, and suitability for battery-powered step-down applications?
Both the LM78S40CN and MC34063A are legacy non-synchronous buck-boost regulators with external switches, but the LM78S40CN supports higher switch current (1.5A vs. 1.5A peak on MC34063A) and wider VIN (2.5V–40V vs. 3V–40V). The LM78S40CN offers better control precision and lower minimum startup voltage, making it slightly more suitable for wide-range battery apps. However, both suffer from low efficiency due to external Schottky diodes and lack of synchronous rectification. For battery designs, prioritize low quiescent current, where neither part excels—consider upgrading to a modern low-IQ buck-boost like the TPS63020 for better runtime, but note the LM78S40CN’s through-hole package simplifies prototyping in legacy systems.
Quality Assurance (QC)
DiGi ensures the quality and authenticity of every electronic component through professional inspections and batch sampling, guaranteeing reliable sourcing, stable performance, and compliance with technical specifications, helping customers reduce supply chain risks and confidently use components in production.
LM78S40CN CAD Models
Texas Instruments LM78S40CN PCB symbols & footprints
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