LM331 V-F Converter: Circuit, Price and Pinout

LM331 is a precision voltage/frequency converter integrated circuit produced by American NS company with high cost performance, simple peripheral circuit, single power supply, and low power consumption. The LM331 has a wide dynamic range of 100dB, an operating frequency as low as 0.1Hz, and has good linearity, and a digital resolution of up to 12 bits. The output driver of LM331 adopts the open-collector form, so the logic level of the output pulse can be flexibly changed by selecting the logic current and external resistance to adapt to different logic circuits such as TTL, DTL and CMOS. LM331 can work between 4.0V and 40V, the output can be as high as 40V, and can prevent VCC short circuit.

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3D Model

★ Guaranteed linearity: 0.01% (maximum) 

★ Low power consumption: 15mW5V

★ Wide comprehensive frequency: 1Hzto100kHz

★ Pulse output compatible with all logic forms

★ Wide dynamic range: 100db

Texas Instruments LM331N/NOPB technical specifications, attributes, parameters and parts with similar specifications to Texas Instruments LM331N/NOPB.

The internal circuit composition of LM331 as shown in the figure is composed of input comparator, timing comparator, RS flip-flop, output drive tube, reset transistor, band gap reference circuit, precision current source circuit, current switch, output protection tube, etc. The drive tube adopts the open-collector form, so the logic level of the output pulse can be flexibly changed by selecting the logic current and external resistance to adapt to different logic circuits such as TTL, DTL and CMOS. LM331 can use dual power supply or single power supply, can work between 4.0 ~ 40V, the output can be as high as 40V, and can prevent Vcc short circuit.

The circuit used by LM331 for V/F conversion is shown below, where CIN is a filter capacitor, and the size is generally 0.1μF; in order to improve the conversion accuracy, the size of RIN is generally 100 kΩ. All devices should try to use materials with high temperature stability, such as metal film resistors. The capacitor is best to choose materials such as NPO ceramic, polystyrene, polytetrafluoroethylene or polypropylene. Pin 2 can be connected in series with a fixed resistor and an adjustable resistor to adjust the errors caused by Rt, Ct and RL. Connecting a 47Ω resistor and a 1μF capacitor to ground in series can improve linearity. Although the size of CL will not directly affect the conversion result, a capacitor with a small leakage current should be selected as much as possible. R1 and R2 are used to adjust the zero output. The relationship between output frequency and input voltage is:

Application Circuit(1)

The figure is a voltage/frequency conversion circuit composed of LM331. LM331 is switched by on-chip reference voltage and current of 1·9v. A monolithic voltage/frequency conversion integrated circuit composed of comparators and flip-flops. In order to expand the measuring range, an A1 operational amplifier is added to the circuit. The reference current IR is set by (Rl+R(RPl)). Since the internal reference voltage is 1·9V, IR=l·9V/(Rl+R(RPl)). The usual setting range is 100-500μA . In addition, the current average value I at the output (pin 1) of the current switch. It is equal to the input current Ii. For the on-chip charging and discharging circuit, when the charging voltage reaches 2A of the power supply voltage, the circuit is reset, so the pulse width is equal to 1·1R4C3. Since the input current Ii is equal to 1·lxR4xC3xf0xIR, the input current Ii is proportional to the oscillation frequency f0, that is, the output frequency f0 is proportional to -Ui.

Application Circuit(2)

Application Circuit(3)

Precision Voltage-to-Frequency Converter, 100KHz Full-Scale

Light Intensity to Frequency Converter

Simple Frequency-to-Voltage Converter, 10KHz Full-Scale

★ Voltage to Frequency Conversions

★ Frequency to Voltage Conversions

★ Remote-Sensor Monitoring

★ Tachometers

Texas Instruments Incorporated (TI) is an American technology company headquartered in Dallas, Texas, that designs and manufactures semiconductors and various integrated circuits, which it sells to electronics designers and manufacturers globally.[6] It is one of the top 10 semiconductor companies worldwide based on sales volume.The company's focus is on developing analog chips and embedded processors, which account for more than 80% of its revenue.TI also produces TI digital light processing technology and education technology products including calculators, microcontrollers and multi-core processors. The company holds 45,000 patents worldwide as of 2016.

Download datasheets and manufacturer documentation for Texas Instruments LM331N/NOPB.