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LM331 Converter: Pinout, Datasheet and Circuit [Video&FAQ]

  • Contents

LM331 is basically a precision voltage to frequency converter from National Semiconductors.

 

Catalog

Product Overview

Related Video Instruction

Circuit Diagram

Features

Principles of Operation

Simplified Voltage-to-Frequency Converter

Block Diagram

Schematic Diagram

Datasheet

Product Attributes

Using Warning

FAQ

 

Product Overview

LM331 is basically a precision voltage to frequency converter from National Semiconductors. The IC has a hand full of applications like analog to digital conversion, long-term integration, voltage to frequency conversion, frequency to voltage conversion. Wide dynamic range and excellent linearity make the IC well suitable for the applications mentioned above.

 

The LM231 /LM331 family of voltage-to-frequency converters are ideally suited for use in simple low-cost circuits for analog-to-digital conversion, precision frequency-to-voltage conversion, long-term integration, linear frequency modulation, or demodulation, and many other functions. The output when used as a voltage-to-frequency converter is a pulse train at a frequency precisely proportional to the applied input voltage.

 

Thus, it provides all the inherent advantages of the voltage-to-frequency conversion techniques and is easy to apply in all standard voltage-to-frequency converter applications. Further, the LM231A/LM331A attain a new high level of accuracy versus temperature which could only be attained with expensive voltage-to-frequency modules. Additionally, the LM231 /331 are ideally suited for use in digital systems at low power supply voltages and can provide low-cost analog-to-digital conversion in microprocessor-controlled systems.

 

And, the frequency from a battery-powered voltage- to-frequency converter can be easily channeled through a simple photo isolator to provide isolation against high common-mode levels. The LM231/LM331 utilie a new temperature-compensated band-gap reference circuit, to provide excellent accuracy over the full operating temperature range, at power supplies as low as 4.0V.

 

The precision timer circuit has low bias currents without degrading the quick response necessary for 100 kHz voltage-to-frequency conversion,  And the output is capable of driving 3 TTL loads, or a high voltage output up to 40V, yet is short-circuit-proof against Vcc-.

 

Video: VOLTAGE to FREQUENCY CONVERTER

LM331 Video Description: The voltage to frequency (V-F) converter accepts an analog input 𝑽_𝒊𝒏 and generates a pulse train with frequency f. Mathematically it is expressed as 𝒇=𝒌𝑽_𝒊𝒏 Where k is the sensitivity of V-F converter in 𝑯𝒛∕𝑽. The op-amp 𝑨_𝟏is comparator while op-amp 𝑨_𝟐 is integrator. When 𝑽_𝒐𝟏 is negative the diode D is forward biased and Capacitor C starts charging.

 

Circuit Diagram

LM331-Circuit

 

Figure: LM331 Circuit

 

Notes

  • The circuit can be assembled on a vero board.
  • I used 15V DC as the supply voltage (+Vs) while testing the circuit.
  • The LM331 can be operated from anything between 5 to 30V DC.
  • The value of R3 depends on the supply voltage and the equation is R3= (Vs – 2V)/ (2mA).
  • According to the equation, for Vs = 15V, R3=68K.
  • The output voltage depends on the equation, Vout = ((R4)/(R5+R6))*R1C1*2.09V*Fin.
  • POT R6 can be used for calibrating the circuit.

 

Features

  • Ensured Linearity 0.01% max
  • Improved Performance in Existing Voltage-to-Frequency Conversion Applications
  • Split or Single Supply Operation
  • Operates on Single 5V Supply
  • Pulse Output Compatible with AIlI Logic Forms
  • Excellent Temperature Stability: +50 ppm/°C max
  • Low Power Consumption: 15 mW Typical at 5V
  • Wide Dynamic Range, 100 dB min at 10 kHz Full Scale Frequency
  • Wide Range of Full Scale Frequency: 1 Hz to 100 kHz
  • Low Cost

 

Principles of Operation

The LM231 /331 are monolithic circuits designed for accuracy and versatile operation when applied as voltage-to-frequency (V-to-F) converters or as frequency-to-voltage (F-to-V) converters. A simplified block diagram of the LM231/331 is shown in the following figure and consists of a switched current source, input comparator, and 1-shot timer.

 

LM331-Principle-of-Operation

Figure: LM331 Principle of Operation

 

Simplified Voltage-to-Frequency Converter

The operation of these blocks is best understood by going through the operating cycle of the basic V-to-F converter, the above-mentioned figure, which consists of the simplified block diagram of the LM231/331 and the various resistors and capacitors connected to it.

 

The voltage comparator compares a positive input voltage, V1, at pin 7 to the voltage, Vx, at pin 6. If V1 is greater, the comparator will trigger the 1-shot timer. The output of the timer will turn ON both the frequency output transistor and the switched current source for a period t=1.1 RtCt. During this period, the current i will flow out of the switched current source and provide a fixed amount of charge, Q = i × t, into the capacitor, CL. This will normally charge Vx up to a higher level than V1. At the end of the timing period, the current i will turn OFF, and the timer will reset itself.

 

Now there is no current flowing from pin 1, and the capacitor CL will be gradually discharged by RL until Vx falls to the level of V1. Then the comparator will trigger the timer and start another cycle. The current flowing into CL is exactly IAVE = i × (1.1×RtCt) × f, and the current flowing out of CL is exactly Vx/RL ≃ VIN/RL. If VIN is doubled, the frequency will double to maintain this balance. Even a simple V-to-F converter can provide a frequency precisely proportional to its input voltage over a wide range of frequencies.

 

Block Diagram

LM331-Block-Diagram

 

Figure: LM331 Block Diagram

 

Schematic Diagram

LM331-Schematic Diagram

 

Figure: LM331 Schematic Diagram

 

Datasheet

You can download the datasheet from the link given below.

LM331-Datasheet

 

Product Attributes

Product Attribute Attribute Value
Source Content uid: LM331N/A+
Manufacturer Part Number: LM331N/A+
Part Life Cycle Code: Obsolete
Ihs Manufacturer: NATIONAL SEMICONDUCTOR CORP
Package Description: DIP, DIP8,.3
Reach Compliance Code: unknown
ECCN Code: EAR99
HTS Code: 8542.39.00.01
Manufacturer: Texas Instruments
Risk Rank: 5.92
Converter Type: VOLTAGE TO FREQUENCY CONVERTER
JESD-30 Code: R-PDIP-T8
JESD-609 Code: e0
Number of Terminals: 8
Operating Temperature-Max: 70 °C
Package Body Material: PLASTIC/EPOXY
Package Code: DIP
Package Equivalence Code: DIP8,.3
Package Shape: RECTANGULAR
Package Style: IN-LINE
Power Supplies: 5 V
Subcategory: Analog Special Function Converters
Supply Current-Max: 8 mA
Supply Voltage-Nom: 5 V
Temperature Grade: COMMERCIAL
Terminal Finish: Tin/Lead (Sn/Pb)
Terminal Form: THROUGH-HOLE
Terminal Pitch: 2.54 mm
Terminal Position: DUAL

Using Warning

Note: Please check their parameters and pin configuration before replacing them in your circuit. 

 

FAQ

  • What makes the IC well suitable for the applications mentioned above?

Wide dynamic range and excellent linearity.

 

  • What is the output when used as a voltage-to-frequency converter?

Pulse train.

 

  • What does the LM231/LM331 utilie?

A new temperature-compensated band-gap reference circuit.

 

  • What type of applications does the LM331 have?

Analog to digital conversion

 

  • What does the LM231/LM331 family of voltage-to-frequency converters provide?

All the inherent advantages of the voltage-to-frequency conversion techniques.

 

  • Where can the LM231/331 provide low-cost analog-to-digital conversion?

Microprocessor-controlled systems.

 

  • What is the power supply of the LM231/LM331?

4.0V.

 

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