How to operate LM741 with single supply

 In this tutorial we will show bias LM741 op-amp correctly so that it can work with single supply voltage. For illustration purpose we will make a non-inverting amplifier using LM741. LM741 is old but very popular operational amplifier and they are still found in the electronics market. Application of LM741 includes Comparators, Multivibrators, DC Amplifiers, Summing Amplifiers, Integrator or Differentiators and Active Filters.


LM741 Integrated Circuit

The LM741 can operate with supply voltage of +22V/-22V dual power supply. But we can also bias the op-amp in order to work with single supply voltage such as +5V. Single supply voltage is helpful in mainly in low powered devices applications.

In order to make LM741 work with single supply we have place a bias circuit the op-amp at the input. There are three biasing techniques- buffer biasing, split resistor biasing and voltage divider biasing. The different biasing techniques was explained in details with example in the tutorial How to bias non-inverting op-amp amplifiers. Here voltage divider biasing technique is used for non-inverting amplifier to amplify ac signal.

The following is the circuit diagram of LM741 using single supply voltage of +5V.

 In the above circuit, the input signal is coupled into the amplifier using the coupling capacitor C1. The resistor R3 is used as DC path which is required when ac coupled amplifier is used. The resistors R1 and R2 forms the voltage divider biasing circuit. This two equal resistors sets the DC voltage at the midvalue of positive power supply(here 5V) and the ground which is 2.5V. Due to this the output signal swings above and below the 2.5V and maximum swing is obtained. The capacitor C2 is the bypass capacitor. The resistors R4 and R5 sets the gain of the non-inverting amplifier(Gain = 1+R4/R5). The C4 is the decoupling capacitor. At the output we have used another coupling capacitor C3 which couples the output signal to the next stage.

The following picture shows LM741 single supply non-inverting amplifier on breadboard.

LM741 single supply on breadboard

This amplifier was tested using Labview software which generates signal via the PC soundcard and plots the input and output signal on oscilloscope. How to connect the signal generator output via loudspeaker and acquire the input/output signal from the amplifier via the line in/microphone input is explained in details in the tutorial Construction of Collector-Emitter Feedback Bias BJT Amplifier Test with PC Oscilloscope and How to Build BJT amplifier and test with Soundcard based PC Oscilloscope. Alternatively you can also use the matlab/simulink PC oscilloscope and spectrum analyzer, see How to use Matlab Simulink as Oscilloscope and LM358 Op-Amp Integrator Test with Matlab Simulink Oscilloscope for this.

The following shows input and output waveform on PC sound card based oscilloscope.

PC oscllioscope LM741 input and output waveform

The following is the spectrum analyzer graph showing the frequency of the input and output signal from the LM741 non-inverting amplifier.

spectrum analyzer of LM741 non-inverting amplifier

 Here in this tutorial we have used voltage divider biasing method to bias the LM741 so that it works with single supply. The next tutorial Biasing LM741 for Single Supply with Split Resistor Biasing demonstrates how to bias LM741 using split resistor biasing method for single supply.

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