LM3909 LED Flasher/Oscillator

Overview

The LM3909 is a monolithic integrated circuit designed primarily as a low-voltage LED flasher and oscillator. This versatile component is engineered to deliver high-efficiency LED flashing capabilities while operating from extremely low supply voltages (as low as 1V). Its unique design uses a timing capacitor for voltage boost, enabling it to produce output pulses sufficient to drive LEDs brightly even when operating from a single 1.5V battery cell.

Originally developed by National Semiconductor, the LM3909 has become a popular choice for battery-operated flashing applications due to its exceptional power efficiency and minimal external component requirements. The device is inherently self-starting and maintains reliable operation across a wide temperature range.

Features

• Ultra-Low Voltage Operation: Functions reliably from 1V to 5V DC
• Exceptional Battery Life: Can operate continuously for over one year from a single C-size flashlight cell
• High-Efficiency LED Driving: Generates bright, high-current pulses to LEDs (2V+ pulses from 1.5V supply)
• Minimal External Components: Requires only a timing capacitor and battery for basic operation
• Low Current Consumption: Averages under 0.5mA during battery life
• Versatile Output Capability: Can directly drive an 8Ω speaker when used as an oscillator
• Wide Temperature Range: Suitable for operation in various environmental conditions
• Cost-Effective Solution: Provides simple, economical flashing functionality

Applications

The LM3909's unique combination of features makes it suitable for numerous applications, particularly those requiring reliable, low-power visual indicators:

• Location Markers: Finding flashlights in the dark or locating boat mooring floats
• Promotional Devices: Sales and advertising attention-getters
• Safety Equipment: Emergency locators for fire extinguishers or other critical equipment
• Entertainment: Toys and novelty items requiring eye-catching flashing effects
• Electronic Circuits: Trigger and sawtooth generators in various electronic designs
• Audio Applications: Siren generation for toy fire engines (combining oscillator and speaker driver functions)
• Warning Indicators: Low-power visual alarms capable of operating from 1.4V to 200V supplies

Electrical Characteristics

Absolute Maximum Ratings

• Supply Voltage: 5V DC
• Power Dissipation: 500 mW
• Operating Temperature Range: 0°C to +70°C
• Storage Temperature Range: -65°C to +150°C
• Lead Temperature (Soldering, 10 sec): 260°C

Recommended Operating Conditions

• Supply Voltage Range: 1V to 5V DC
• Operating Temperature Range: 0°C to +70°C
• Timing Capacitor: 100μF typical (value determines flash rate)
• LED Current: 10mA to 20mA peak (pulsed)

Performance Characteristics

• Oscillation Frequency: Adjustable via timing capacitor (typically 1Hz to 10Hz)
• Output Pulse Voltage: 2V minimum (with 1.5V supply)
• Quiescent Current: Typically 0.3mA between pulses
• Start-up Time: Immediate (self-starting design)
• Duty Cycle: Approximately 10% (adjustable with circuit modifications)

Package Information

Physical Specifications

• Package Type: 8-pin DIP (Dual In-line Package)
• Package Designator: N08E
• Order Number: LM3909N
• Dimensions: 9.81mm x 6.35mm x 3.3mm (typical)
• Lead Pitch: 2.54mm (0.1 inch)
• Lead Material: Copper alloy
• Finish: Matte tin plating
• Weight: Approximately 0.5 grams

Pin Configuration (Top View)

• Pin 1: Timing Capacitor (+) terminal
• Pin 2: Ground
• Pin 3: Output (LED connection)
• Pin 4: Not Connected
• Pin 5: Positive Supply Voltage
• Pin 6: Timing Capacitor (-) terminal
• Pin 7: Not Connected
• Pin 8: Speaker Drive (when used as oscillator)

Typical Application Circuit

The most basic implementation of the LM3909 requires only three external components:

• 1.5V battery (AA, C, or D cell)
• 100μF electrolytic timing capacitor
• Standard LED (any color)

For variable flash rate applications, the timing capacitor value can be adjusted - larger values result in slower flash rates, while smaller values increase the flash frequency. The circuit can be easily modified to drive multiple LEDs in series or parallel configurations, though current-limiting resistors may be required for parallel LED arrangements.

Design Considerations

When implementing the LM3909 in a design, several factors should be considered:

• Battery Selection: Alkaline batteries provide longest life; rechargeables may require circuit adjustments
• Capacitor Quality: Use low-leakage electrolytic capacitors for most reliable timing
• LED Characteristics: Standard efficiency LEDs work well; high-brightness types may require current limiting
• Environmental Factors: Extreme temperatures may affect flash rate and capacitor performance
• Power Supply Decoupling: For non-battery applications, include a small bypass capacitor near the IC