How do you generate saw tooth waveform from op amp741?

Answer 1

Use the 741 op amp in the integrator configuration. to do this you need to place one end of resistor to negative terminal of opamp and then connect a capacitor from the negative terminal of the opamp to its output. Then provide input voltage to the other unused end of the resistor. (you must also power up your 741 seperately, see data sheet for those info). so what you have is an opamp in the 'non-inverting' configuration except that the resistor that connects the negative terminal of the opamp to its output, is replaced by a capacitor. Now that you have done that.. you need to provide a 'pulse train' with a certain frequency(try 1kHz). the integration of a pulse train gives you a sawtooth function. have fun by playin aroud by changing the frequency and see what happens, also use a potentiometer instead of the resistor to see what happens when you change the resistance value.

Answer 2

One option to generating a sawtooth wave with an opamp (or two) and a few extra components is...

Ground the positive input of an opamp U1.

R1 is a potentiometer, used to set frequency. R2 is a fixed resistor, chosen to limit the maximum frequency rate. R1 and R2 are in series between the U1 negative input and the negative rail.

Choose a capacitor C1. It can be non polarized or electrolytic, as desired, since it will only be charged in one direction. Look at the differential equation for a capacitor ...

dv/dt = i/c

... so if you want (for example) a slope of 1 volt per millisecond, with a reference current of 1 milliamp, you would choose a value of 1 microfarad. That reference current is determined by the negative supply voltage divided by R1 + R2. Scale accordingly, but remember that at lower capacitance values and higher frequencies, parasitic capacitance and inductance will start to have an effect.

Connect C1 between U1 negative input and R3, with the other end of R3 connected to output. R3 is chosen to limit the transient on U1 when C1 is later shorted, but should be relatively small in comparison with R1 + R2, but not too small. If C1 is electrolytic, connect the negative terminal to the negative input. (The value of R3, within limits, does not affect the frequency of the oscillator, because U1 is operating as a constant current source.)

At this point, you have a circuit which will charge C1 linearly until U1 reaches its limits, with slope set by R1. Now we need to reset C1...

Connect an SCR S1 and resistor R4 in series across C1. The cathode goes to the negative side (negative input of opamp) and R4 is between the anode and the junction of C1/R3. R4 could be zero, but if C1 is electrolytic, it should be some very small value to limit discharge current and protect S1.

Connect a zener diode Z1 across the anode and gate of S1, anode to gate and cathode to anode. The reference voltage of Z1 should be about 0.6 volts less than the trip point, which must also be a few volts less than the positive supply voltage.

Last, connect a resistor R5 between S1 gate and S1 cathode. R5 should be relatively high value - it is there to prevent parasitic firing of S1.

At this point, you have an operational sawtooth generator, with frequency adjusted by R1. The output, at the junction of C1 and R3, starts near zero, rises to the Z1/S1 trigger voltage with slope set by R1, and then discharges rapidly through R4. If the trip point was 10 volts, C1 was 1 microfarad, and the reference current was 1 milliamp, the frequency would be about 100 Hz.

If the output needs to be buffered, you can do so with a second opamp U2. Connect C1/R3 to the U2 positive input, and the U2 output connected to its negative input.

The output has a DC bias. To remove that bias, you can put a high value resistor between C1/R3 and the positive input of U2. Then add a high value potentiometer R6 between the power supply rails, with the wiper also connected to the U2 positive input. As you adjust R6, the output will shift up and down, within limits of U2.