onsemi MC7809BT

Overview

MC7809BT from onsemi is a fixed-output, 9.0 V, 1.0 A positive linear voltage regulator in TO-220 package with internal thermal shutdown, short-circuit current limiting, and safe-area compensation. It delivers stable 9 V output across 5 mA–1.0 A load range with ≤±5% total output variation (including line/load/temp), supports input voltages up to 35 V, and is used for local regulation in industrial power supplies, automotive control modules, and embedded system rails.

For engineers reviewing the MC7809BT datasheet, pinout, applications, or equivalent options, this page provides verified electrical specs, thermal behavior, PCB layout guidance for heatsinking, and validated drop-in alternatives for cost, availability, or qualification-sensitive designs.

Technical Context

The MC7809BT implements a monolithic series-pass transistor architecture with built-in protection circuitry: thermal overload detection triggers shutdown at +150°C junction temperature, while current-limiting circuitry caps peak output at 2.2 A and short-circuit current at 0.2 A. Its dropout voltage remains fixed at 2.0 V (at 1.0 A, 25°C), independent of output voltage variant.

It operates without external components for basic regulation but requires input bypassing (≥0.33 µF) when placed remotely from bulk filtering. Output capacitance is not required for stability but improves transient response; values below 0.1 µF may cause instability per datasheet guidance.

Key Specifications

Pinout & Package

MC7809BT uses the industry-standard TO-220 package (Case 221AB), with metal tab electrically connected to Pin 2 (Ground). Heatsinking is mandatory for >500 mA continuous operation due to thermal resistance of 92°C/W (junction-to-ambient).

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM7809CT, MC7809BT offers superior ripple rejection and lower quiescent current-critical for battery-backed or noise-sensitive designs-while NCV7809BDT adds automotive qualification without electrical trade-offs, making it ideal for Tier 1 supply chain compliance.

Availability

MC7809BT is available at Aetrix Electronics and suitable for industrial control power, automotive body electronics, and embedded system core rails requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for MC7809BT 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 specializing in energy-efficient power management, analog, and sensor solutions for automotive, industrial, and cloud infrastructure markets.

The MC7800 series was designed as a robust, drop-in-replacement family of fixed-output linear regulators targeting cost-sensitive, high-reliability applications where simplicity, protection, and proven thermal behavior are prioritized over ultra-low quiescent current or adjustable output.

FAQ

What is the maximum input voltage for MC7809BT?

The absolute maximum input voltage for MC7809BT is 35 V DC, as specified in the Maximum Ratings table. Operation above this voltage risks permanent damage. For reliable 1.0 A continuous output, input should remain within 11.5–24 V per electrical characteristics-ensuring ≥2.0 V dropout margin and staying within safe power dissipation limits with appropriate heatsinking.

Does MC7809BT require an output capacitor for stability?

No, MC7809BT does not require an output capacitor for stability-its internal compensation ensures unconditional stability. However, adding a 0.1–10 µF ceramic or tantalum capacitor at the output significantly improves transient response to load steps. Values below 0.1 µF may cause instability, per datasheet guidance in the Applications Information section.

Can MC7809BT be used in automotive applications?

Standard MC7809BT is not AEC-Q100 qualified and is not recommended for automotive safety-critical or under-hood applications. For automotive use, select the NCV7809BDT variant-identical in pinout and electrical specs but fully qualified to AEC-Q100 Grade 1 (−40°C to +125°C) with PPAP capability and enhanced process controls.

What thermal considerations apply to MC7809BT at 1.0 A output?

At 1.0 A and 24 V input, MC7809BT dissipates ~15 W (15 V × 1.0 A). With R_JA = 92°C/W (TO-220, no heatsink), junction temperature would exceed 150°C instantly. A heatsink reducing R_JA to ≤30°C/W is mandatory. Mounting the tab (Pin 2) to a ≥25 cm² copper pour with thermal vias is the minimum practical solution for sustained 1.0 A operation.

How does MC7809BT handle short-circuit conditions?

MC7809BT employs dual protection: short-circuit current limiting caps output at ≤0.2 A (typical), and thermal shutdown activates if junction temperature reaches +150°C. During a sustained short, the device cycles between current limit and thermal shutdown-limiting average power and enabling safe recovery once the fault is removed, without requiring manual reset.