onsemi MC78L09ACP

Overview

MC78L09ACP from onsemi is a 100 mA, fixed +9.0 V positive linear voltage regulator in TO-92 package with internal short-circuit and thermal overload protection. It delivers stable output under 1.0–100 mA load, requires no external components in basic configurations, and supports industrial temperature range (0°C to +125°C). It is widely used in low-power sensor interfaces, microcontroller supply rails, and legacy analog subsystems.

For engineers reviewing the MC78L09ACP datasheet, pinout, applications, or equivalent options, key selection criteria include dropout voltage (1.7 V typical), line/load regulation (≤125 mV/≤40 mV), thermal resistance (200°C/W in TO-92), and compatibility with standard 0.33 µF input / 0.1 µF output capacitor configuration.

Technical Context

The MC78L09ACP implements a monolithic series-pass transistor regulator with built-in current limiting and thermal shutdown circuitry. Its internal architecture includes error amplifier, reference voltage generator, and pass element - all integrated into a single silicon die without external feedback network.

It operates as a three-terminal device requiring only input, ground, and output connections. Input-to-output differential must remain ≥2.0 V during ripple minima to maintain regulation, and its quiescent current is ≤6.0 mA at +125°C - enabling predictable power budgeting in battery-backed or thermally constrained designs.

Key Specifications

Pinout & Package

MC78L09ACP uses the industry-standard TO-92 plastic package (Case 029), with leads formed for straight-lead bulk or tape-and-reel packaging. Thermal performance is optimized for PCB mounting with minimal copper area.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar fixed-voltage linear regulator applications.

Compared with MC78L09ACP, the SOIC-8 MC78L09ACDR2G offers better manufacturability but requires PCB redesign, while LM78L09ACZ trades off regulation precision and thermal margin for second-source availability - making MC78L09ACP optimal for cost-sensitive, through-hole industrial applications demanding tight voltage tolerance and robust thermal behavior.

Availability

MC78L09ACP is available at Aetrix Electronics and suitable for industrial sensor interfaces, legacy microcontroller power supplies, and low-power analog instrumentation requiring stable component supply and long-term obsolescence management.

Supply support for MC78L09ACP includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

onsemi (formerly ON Semiconductor) is a global semiconductor supplier delivering energy-efficient, intelligent power and sensing solutions for automotive, industrial, cloud, medical, and IoT applications.

The MC78L00A Series was designed specifically for cost-sensitive, low-current linear regulation tasks where simplicity, reliability, and long-lifecycle support outweigh switching efficiency - targeting industrial controls, legacy equipment upgrades, and analog subsystems.

FAQ

What is the maximum input voltage for MC78L09ACP?

The absolute maximum input voltage for MC78L09ACP is 35 Vdc for devices rated at 12–18 V output, but per the datasheet's Absolute Maximum Ratings table, the 9 V variant (MC78L09A) has a 35 V limit for 12–18 V input ranges - however, the specific entry for 9 V devices lists "Input Voltage (12 V–18 V)" as 35 V. For safe continuous operation, input should not exceed 24 V to maintain regulation margin and avoid excessive power dissipation in the MC78L09ACP.

Does MC78L09ACP require input and output capacitors?

Yes - the MC78L09ACP requires a 0.33 µF input capacitor (tantalum, mylar, or low-ESR ceramic) placed close to the input pin to ensure stability, especially with long traces or high source impedance. An output capacitor (0.1 µF) is not mandatory for stability but improves transient response and is strongly recommended in all MC78L09ACP applications per the datasheet's Figure 2 and Applications Information section.

What is the thermal resistance of MC78L09ACP in TO-92 package?

The thermal resistance, junction-to-ambient (R_JA), for MC78L09ACP in TO-92 package is 200°C/W, as specified in the Thermal Characteristics table on page 2 of the datasheet. This value assumes no heatsink and standard PCB mounting - actual R_JA improves with increased copper area, but the MC78L09ACP's 625 mW max power dissipation at 25°C ambient is derived directly from this R_JA.

Is MC78L09ACP suitable for automotive applications?

No - MC78L09ACP is rated for 0°C to +125°C operation and is not AEC-Q100 qualified. For automotive use, the NCV78L09ABPRAG (−40°C to +125°C, AEC-Q100 qualified, TO-92) is the designated automotive-grade variant. The "C" suffix in MC78L09ACP denotes commercial/industrial temperature grade, not automotive qualification.

Can MC78L09ACP be used as a current source?

Yes - the MC78L09ACP can be configured as a constant-current source per Figure 9 in the datasheet. By connecting the input to a higher voltage rail, grounding the output through a sense resistor R, and returning the regulator ground to the load return, output current equals (9.0 V / R) + I_IB. For example, with R = 90 Ω, MC78L09ACP delivers ~100 mA (plus ~3–6 mA bias current), making it viable for LED bias or sensor excitation where moderate accuracy suffices.