LM2931AZ-5 5V LDO Voltage Regulator 100mA TO-92 National Semiconductor

National Semiconductor LM2931AZ-5 Low Dropout 5V Regulator - 60V Load Dump Protected, TO-92 Through-Hole

Condition

Unused NOS. Markings legible: N78BV / LM293 / 1AZ-5 on the TO-92 body; circled V logo molded on face. Three straight leads show light oxidation patina consistent with long-term storage. Sourced from an electronics distributor consolidating inventory.

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Product Overview

National Semiconductor LM2931AZ-5 - a fixed 5.0V LDO linear voltage regulator in a 3-pin TO-92 through-hole package. Converts input voltages up to 26V continuous down to a stable 5.0V rail at up to 100mA, with transient protection to 60V. Designed specifically for automotive and battery-powered environments where load-dump events and reverse battery conditions would destroy a standard 78L05.

Key Features

• Fixed 5.0V output, 100mA maximum continuous output current
• Input voltage range: up to 26V continuous; withstands transients to 60V
• Dropout voltage: 0.2V typical at 10mA load; under 0.6V at 100mA
• Quiescent current: 1mA or less at 10mA load
• 60V load-dump transient protection - automotive-grade resilience
• Reverse battery protection built in
• Mirror-image insertion protection - guards against accidental reverse installation
• 3-pin TO-92 package: Pin 1 Output, Pin 2 Ground, Pin 3 Input
• A-suffix output voltage accuracy grade

Applications

• Replacing a failed 5V regulator on an automotive ECU, instrument cluster, or sensor module - especially where 60V load-dump events have taken out previous regulators
• Powering a microcontroller or sensor rail from a multi-cell battery pack, squeezing out extra runtime because the LDO keeps regulating as the battery sags
• Fixing a handheld meter or remote telemetry unit where the existing 5V rail regulator has failed and the board uses a through-hole TO-92 footprint
• Breadboard prototyping of battery-powered 5V circuits where a standard 7805 would waste too much headroom or lack reverse protection
• Restoring vintage automotive accessories and aftermarket modules that originally specified the LM2931 family

Frequently Asked Questions

Can I drop this straight into a board designed for a 78L05?

Check the pinout before soldering. The LM2931AZ-5 in TO-92 is Pin 1 Output, Pin 2 Ground, Pin 3 Input. The 78L05 in TO-92 uses a different pin arrangement. A direct swap without verifying pad assignments will likely apply input voltage to the wrong pin.

What output capacitor does this require?

The LM2931 requires an output decoupling capacitor of 10µF or higher with adequate ESR to maintain loop stability. Low-ESR ceramic capacitors used alone can cause oscillation in legacy LDO designs - add a small series resistor if you are using ceramics.

Is this suitable for 12V automotive use with load-dump events?

Yes. The LM2931AZ-5 is rated for continuous input up to 26V and withstands transient spikes to 60V, which covers automotive load-dump conditions. It also includes reverse battery protection, making it a purpose-built drop-in for automotive 5V supply applications where a standard regulator would be at risk.

Will this work for a 5V Arduino or microcontroller supply from a Li-ion pack?

Yes, within the 100mA output limit. If your microcontroller and attached peripherals draw under 100mA total, the LM2931AZ-5 will regulate 5V from a Li-ion pack down to near-depleted voltage levels due to its low dropout. Confirm your total current draw before committing to the design.

The 78L05 does one job reasonably well - until the car battery throws a 60V spike at it. The LM2931AZ-5 was built for exactly that moment, and this one has been waiting in a parts bin ever since. Now it is yours to put to work.