What Is an LM3914N-1 IC?

What Is LM3914N-1?
- The LM3914N-1 is a monolithic integrated circuit to display an analog signal level with a series of LEDs.
- The LM3914N-1 can drive up to 10 LEDs in either a bar graph or dot mode.
- It is useful for applications such as battery level indicators, audio VU meters, and other measurement displays where a visual representation of a variable signal is needed.
- The LM3914N-1 operates over a wide voltage range (typically 3-18V) and includes an adjustable reference voltage to tailor the range of the displayed signal.
- It features built-in LED current regulation.
Pinout of LM3914N-1
LED1 - Drives the first LED in the series, indicating the lowest level.
V- - Ground pin (negative power supply).
V+ - Positive power supply voltage input.
RLO - Lower reference voltage input, used to set the minimum threshold for the signal display.
SIG - Signal input pin; this is the analog input voltage to be displayed.
RHI - Upper reference voltage input, used to set the maximum threshold for the signal display.
REFOUT - Reference output, provides a stable reference voltage for other parts of the circuit if needed.
REFADJ - Reference adjustment, used to set the reference voltage for the display range.
MODE - Mode selection pin, selects between bar mode (all LEDs up to the signal level lit) and dot mode (only one LED lit at the signal level).
LED10 - Drives the tenth (highest) LED in the series, indicating the highest level.
LED9 - Drives the ninth LED in the series.
LED8 - Drives the eighth LED in the series.
LED7 - Drives the seventh LED in the series.
LED6 - Drives the sixth LED in the series.
LED5 - Drives the fifth LED in the series.
LED4 - Drives the fourth LED in the series.
LED3 - Drives the third LED in the series.
LED2 - Drives the second LED in the series.
Circuit of LM3914N-1
The LM3914N-1 converts analog signals into LEDs in the form of dots or bars to indicate the magnitude of the input voltage. The circuit principle is based on the operation of a network of comparators and voltage dividers.The LM3914N-1 has an internal 10-segment voltage divider and 10 comparators, which divide the input signal (SIG) into 10 different voltage ranges by means of set upper and lower voltage limits (RHI and RLO pins). A change in signal voltage causes the corresponding comparator to energize, which drives the corresponding number of LEDs to illuminate, indicating the number of LEDs illuminated at the current voltage level.
In terms of circuit flow, the input voltage (SIG) of the LM3914N-1 is first processed by the voltage divider network, and the internal comparator compares it to the preset voltage intervals one by one. For voltages higher than the specified range, the corresponding LED output pins (LED1 - LED10) of the LM3914N-1 will turn on, causing the LEDs to illuminate. The display sensitivity and display range can be set by adjusting the REFADJ pin, while the MODE pin selects the display mode. In bar display mode, all LEDs below the signal voltage are illuminated, while in dot display mode, only a single LED corresponding to the signal voltage is illuminated.
Specification of LM3914N-1
Voltage - Supply: 3V to 20V
Reference Voltage Output: 1.25V ~ 12V
Input Signal Range: 0V ~ 1.2V
Current - Supply: 6.1 mA
Operating Temperature: 0°C ~ 70°C
LED Outputs: 10 independent LED outputs
Accuracy: ±1 dB over temperature range
Response Time: 2.5 ms
Package / Case: 18-DIP
Features of LM3914N-1
- Drives LEDs, LCDs or Vacuum Fluorescents
- Bar or Dot Display Mode Externally Selectable by User
- Expandable to Displays of 100 Steps
- Internal Voltage Reference from 1.2V to 12V
- Operates with Single Supply of Less than 3V
- Inputs Operate Down to Ground
- Output Current Programmable from 2 mA to 30 mA
- No Multiplex Switching or Interaction Between Outputs
- Input Withstands ±35V without Damage or False Outputs
- LED Driver Outputs are Current Regulated, Open-collectors
- Outputs can Interface with TTL or CMOS Logic
- The Internal 10-step Divider is Floating and can be Referenced to a Wide Range of Voltages
Package of LM3914N-1
The LM3914N-1 is available in an 18-pin dual in-line package (18-DIP) with the pins arranged on two parallel rows with nine pins on each side. This package format is easy to insert into the corresponding slots in breadboards or circuit boards for quick installation and removal. 18-DIP packages have good thermal performance and are ruggedized for use in electronic circuits that require high reliability and stability.
Where to Use LM3914N-1?
The LM3914N-1 is capable of providing intuitive visual feedback by converting an incoming voltage signal into a 10-level LED indicator display. Typical applications include battery level indication, audio level display, and temperature display. For example, in a battery level monitoring system, the LM3914N-1 can display the voltage status of the battery in real time to help users understand the remaining battery power.
In addition, the LM3914N-1 is also widely used in instrumentation and audio equipment. For example, in audio equipment, the LM3914N-1 can display the level of the audio signal, allowing users to easily observe the audio output signal strength through the LED display. It can also be integrated in temperature monitoring devices to display temperature changes by measuring the output voltage of a temperature sensor.
How to Test LM3914N-1?
To test the LM3914N-1, you can start by building a simple circuit on a breadboard and connecting the power supply and the ICs. First, connect V+ (pin 3) to a power supply and ground V- (pin 2). Next, connect the LEDs to pins 1, 10, and 18 in order to limit the current.
Then, connect a variable voltage source (such as a potentiometer) to the signal input (pin 5). Starting from the lowest voltage position of the potentiometer, gradually increase the voltage. As the voltage increases, observe that the LEDs light up sequentially. This indicates that the IC is correctly measuring and displaying the input signal. To confirm the IC's functionality, adjust the voltage across the range to ensure that each LED lights within the corresponding voltage range to reflect the IC's linear display output.
FAQs
How does the LM3914N-1 work?
The LM3914N-1 measures an input voltage and translates it into a corresponding LED output. As the input voltage rises, the IC progressively lights up more LEDs along a 10-step scale, either in a bar or dot mode.
What’s the difference between bar mode and dot mode on the LM3914N-1?
In bar mode, all LEDs up to the selected level light up, creating a continuous bar. In dot mode, only one LED at the current voltage level lights up. Dot mode can be set by connecting pin 9 to ground, and bar mode is set by leaving pin 9 unconnected or connecting it to a positive voltage.
Can the LM3914N-1 drive high-current LEDs directly?
The LM3914N-1 can source up to 30mA per LED, so it can handle standard LEDs directly. However, for higher-current LEDs, an external transistor may be needed to amplify the current.