[moved] Squarewave Generator using LM741

[imranahmed]

Please let me know that I built Squarewave generator using LM741 opamp but it

could not generate any output.

Please see attachment.

 

[Easyrider83]

Re: Squarewave Generator using LM741

Try to specify parameter for C1: "precharge = 0"

 

[BradtheRad]

Re: Squarewave Generator using LM741

The 741's output cannot go lower than 2V above its low supply rail. Therefore the 741 needs a bipolar supply.

This relaxation oscillator will only work if the output goes down to 0V or into negative region. It may be sufficient if you make the lower supply rail -1 or -2V.

 

[E-design]

Try this modification.

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If you want the output to switch down to zero, you can add a transistor like shown.

 

[imranahmed]

Thank you E-design

I'll do this.

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Dear bradtheRad,

I set low and high rail at +12 and -12

 

[E-design]

Make sure you are using an opamp model that can simulate. Some are only for schematic purposes and do not have a simulation model attached. It should work with your +12/-12 supply as you can see here.

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Make sure there is an SPICE model attached.

 

[imranahmed]

Thank you dear E-design, its working.

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Dear E-design.

I want to generate 25kHz square wave but when I set C1=0.001uF and R1=18k-Ohms.

For example:

C1=0.001uF , R1=18k-Ohms

According to,
F=1/(2.2 * R1 * C1)

F = 25.2 kHz.

But it could not generate 25kHz pulses.

 

[Audioguru]

The lousy old 741 opamp design is 47 years old. It was designed for DC and low frequencies. Its datasheet shows that it has slew rate problems above 9kHz. Also, at 25kHz its voltage gain is fairly low.
To produce a half decent 25kHz squarewave it must produce the harmonics that are 250kHz and higher.

 

[imranahmed]

Dear Audioguru,

Please recommend me any opamp or IC to generate precise square wave.

 

[KlausST]

Hi,

use a push-pull comparator.

like this:


Klaus

 

[E-design]

The older LF351 or a TL071 should work well for you.