![]() Read this article: Triangular wave generator for a better understanding on opamp integrators. Since the integrator is wired in inverting mode, the sawtooth wavform falls when the timer output is high and rises when the timer output is low. Resistor R4 in conjunction with capacitor C3 sets the bandwidth. Resistors R3 and R4 sets the gain of the opamp integrator. The assymmetric square wave obtained at the output of NE555 is integrated by the inverting active integrator based on opamp IC uA741. Read this article : NE555 as astable multivibrator for a better understanding on NE555 based astable multivibrators. The charging time period (ON time) is given by the equation T1= 0.69(R1+R2)C1 and the discharging time period (OFF time) is given by the equation T2=0.69R2C1. ![]() This action is repeated and the result will be a square wave at pin 3 of the NE555. As a result the output of the timer( pin 3) goes low. ![]() When the voltage across capacitor C1 becomes less than 1/3Vcc, the lower comparator inside the IC switches to positive saturation and this again triggers the internal flip-flop. Now the capacitor C1 starts to discharge through resistor R2 into pin 7 of the IC. This makes the output (pin 3) of the timer low. When the voltage across C1 is above 2/3Vcc the upper comparator inside the NE555 swings to positive saturation and this triggers the internal flip-flop. When the power supply is switched ON, capacitor C1 starts charging through resistors R1 and R2. The working of the astable multivibrator is given below. The asymmetric square wave is available at pin 3 of the IC. The value of these components are so selected that the OFF time is less than 10% of the ON times. The the resistor R1, R2 and capacitor C2 sets the ON and OFF time periods. Here the IC NE555 is wired as an astable multivibrator with unequal ON and OFF times. Here an NE555 timer IC is used for generating the assymmetric square wave and opamp integrator based on uA741 is used for integrating the assymmetric square wave. The circuit shown below shows a setup for generating sawtooth wave. ![]() Sawtooth waveforms can be generated by integrating square waves with unequal rise and fall times (asymmetrical square waves). ![]() Sawtooth wave generator using NE555 timer and uA741 opamp. Like triangular waveforms, sawtooth waveforms are also used in applications like thyristor (SCR, triac etc) switching, sampling, tone/frequency generation, modulation etc. ![]()
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