sawtooth waveform using 555 IC or opamp?

[rudr_p]

Hi, I need a sawtooth wave of +/-15v(little less than that will also do) of about 12khz or more. the two op amp circuit (schmitt trigger and integrator method) but will it work with lm324 or 339 opamp?................. another option I see is 555 ic timer for as square wave generator and opamp. I have +/- 15v available.
is there another method to obtain the waveform?

 

[schmitt trigger]

The integrator method will produce a triangular waveform, not a sawtooth...which one do you really need?

The easiest way to produce a sawtooth is with an UJT (unijunction transistor) oscillator, which consists of exactly three components: the UJT itself, a resistor and a capacitor.

The circuit can be further enhanced with another resistor on base 2 for temp stability, and if you want the sawtooth to be really linear, with a current source instead of the charging resistor. You can roll your own or use a LM334 in a temperature compensated configuration (see figure 15 in the datasheet).

Lastly you need to buffer said sawtooth, in which case the LM324 is a good option (as long as you keep the sawtooth at a low frequency, say 200 Hz max). At higher frequencies you may want to use a TL074, or any other opamp with a higher slew rate.
Since the TL074 is a FET input device, it will load your circuit far less, and therefore that would be my opamp of choice even if I were generating low frequencies.

 

[rudr_p]

thank you schmitt trigger for your reply. I am skeptic if ujt or tl074 is available in my office's inventory but i'll see what I can get there.

 

[Audioguru]

The LM324 quad and LM358 dual opamp's are low power which causes them to be slow. They have trouble with high level sinewaves above about 2kHz so a triangle wave above about 200Hz will be fairly messed up.
Any half-decent audio opamp like the TL071 single, TL072 dual and TL074 quad work well up to 100kHz so they can produce a good triangle wave up to about 10kHz.

 

[Borber]

If supply voltage equals requested amplitude of signal you must use rail-to-rail output device. Some CMOS rail-to-rail OPAs can do it.

 

[schmitt trigger]

Then check figure 23 on the LM555 datasheet.

I'm looking at TI's datasheet. Other manufacturers may show the same circuit but with a different figure number.

You will still have to buffer the waveform with an opamp. Use the TL074, and if not available at your office, purchase one.
The TL074 is also a very mature device and should be both widely available and low cost.

 

[D.A.(Tony)Stewart]

How fast slew rate do you need? 100x ramp? 1000x ramp?
Ramp= 30V/0.833ms = 36kV/s

Thus 1000x Ramp = 36V/μs

FYI only in choosing circuit.

 

[crutschow]

Below is the simulation of an all transistor sawtooth generator. It uses a current-mirror constant-current source (Q3, Q4) to linearly charge C1. C1 is then rapidly discharged by the regenerative switch (Q1 & Q2) at the peak of the waveform (as determined by voltage divider R1 and R2).

It's maximum output amplitude is from about 0.5V to a little over 26V with a 30V supply. For a ±15V supply just connect the minus 15V output in place of all the ground connections on the schematic. The frequency can be varied by pot U1 from about 8kHz to 24kHz for the C1 value shown.

Q5 and Q6 form a complimentary emitter-follower circuit to buffer the output.

Note that R4 should be a 1/2W resistor. If you can tolerate a higher output impedance changing R4 to 2KΩ allows it to be a 1/4W size.

 

[crutschow]

By changing the value of R2 to 30kΩ in my circuit, the maximum peak voltage increases to over 28V.

 

[BrunoARG]

Such a high voltage variation will need a fast opamp such as LM318 (single OP-amp).

The signal generation could be done at lower voltages with a cheap opamp (double) and be amplified by the fast one.

A displaced integrator with a schmitt trigger can generate a sawtooth (I reached a 97% duty triangle with that method), and then you amplify the output with a non-inverting amplifier using the fast op amp. LM318 can be supplied with +-18V so you're done with that.

 

[rudr_p]

Thank you guys for your valuable suggestion. I used TL074 for generating the triangular wave and by setting the pulse width I got almost sawtooth wave.