Introduction to Lm324n

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Electrical Engineering

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Electronics Engineering

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Mechatronics Engineering

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Introduction to Lm324n

• Lm324n is a high gain voltage amplifier that comes with differential input and single ended output.
• It is designed in such a way, that the voltage difference between input terminals creates an output signal of much larger magnitude.

• It consists of four independent op-amp that are incorporated in a single 14 pin DIP package.
• Operational amplifiers are the initial devices that were used in analog computer to perform many mathematical operations in many nonlinear and linear circuits.
• Lm324n mostly operates on a single power supply and with wide range of voltages.
• We can also operate this device on a split power supply however, supply current drain doesn't depend on the strength of supply voltage.
• The characteristic of this circuit, its band width, impedance, and input don't effect manufacturing variations and temperature coefficient because this op-amp exhibits negative feedback.
• Op-amp are widely used in many electronic applications as oscillator, rectifier and comparators  and are most common scientific devices these days.
• Output voltage of this amplifier goes to ground and it also allows direct sensing ground. Lm324n is compatible with all forms of logic circuits.
• Power drain incorporated in this amplifier is suitable for battery operation.
• In the linear mode of operation, voltage ranges between ground and out put voltage.
• The unity gain cross frequency and input bias current of this amplifier is temperature compensated.

• Normally operational amplifiers amplifies the difference between the input voltage which is normally called the differential input voltage.
• The differential inputs of this amplifier consists of inverting input voltage with V_ and non-inverting input voltage with V+. The output of the this op-amp is given by

V(out)= AoL(V+ _ V_)

• Here AoL represents the open loop gain of the amplifier. As it is an open loop gain so it doesn't contain feedback from output to the input.
• The magnitude of AoL is very high sometimes goes to 100,000, so small difference between non-inverting and inverting voltages magnifies the output voltage to nearly supply voltage.
• A state in which output voltage is equal or greater than input supply voltage is called saturation state of the amplifier.
• It is important to note magnitude of open loop gain of the amplifier can not be controlled by the manufacturing process, so open loop amplifier can not be used as a standalone differential amplifier.
• Op-amp is behaved like a comparator in the absence of negative feedback.
• If positive voltage is applied at the non-inverting terminal and inverting terminal is set to ground with the help of resister, then the output will turn out to be maximum positive and if negative voltage is applied on the non-inverting terminal the output voltage will be maximum negative.

Lm324n Pinout

• It mainly consists of 14 pins. Function of each pin is shown in the figure below.

• Lm324n operates on a single power supply and contains true differential inputs that operate in linear mode.
• It can operate over a multiple range of power supply voltage which have little impact on performance characteristics.
• At 25 ºC, Lm324n can operate over a minimum voltage supply of 2.3V.

Absolute Maximum Rating Lm324n

• It is important to note that input voltage shown in the figure above will only exist when voltage at any input terminals is driven negative.
• This happens because collector base junction of PNP transistors turns to forward biased mode, which ultimately behaves as input diode clamps.
• This transistor action allows the output voltage oscillates between positive voltage supply and ground.
• It will only happen between the time duration when input is driven negative.
• Short circuits from output to the positive supply voltage can create excessive heating which ultimately damages the device.

Functional Block Diagram

• There is no need of diodes for differential voltage protection because large differential input voltages don't exhibit large current.
• The differential input voltage can exceed from input positive voltage without harming the device.
• However, protection must be needed in order to avoid input voltage from going too negative below than _ 0.3 V. A simple diode with resistor can be used as a protection on the input of voltage terminals.
• In order to minimum the power drain, these amplifies have Class A output stage for small signals which evidently convert to Class B out put stage for large signals.
• This action causes the amplifiers to sink and source the large current. Both, NPN and PNP resistors can be used to increase the power intensity of the basic amplifiers.
• In most of the AC application, output of the load is capacitively connected with amplifier, A resistor must be connected to the amplifier out put and ground in order to avoid crossover distortion and to enhance class A bias current.
• No cross over distortion is observed when out put load is directly connected with the amplifier.

Applications

• Lm324n is widely used in transducer amplifiers.
• DC gain blocks and conventional amplifiers circuits are mainly consists of Lm324n.
• It can be used as a rectifier, oscillator and comparator.