LM393 comparator issue #2

Thread Starter

Arijeet

Joined Dec 27, 2019
78
In my Lm 393 comparator, my output is not coming proper square wave.picture is shown below.i have described about my circuit. practically
I am using voltage comparator LM393 for comparing two signals, one signal is my reference signal which is a triangle wave, with voltages 2.08 volt generated by 555 timers above 200kHZ giving to the input terminal of inverting side of LM393 and input signal or modulating signal which voltage is less than 2.08 giving from function generator as a sinusoidal signal in the range of 1 Hz to 20kHz in the noninverting side of LM393. My question is when I am providing two signals it should be compared and give a square wave, but LM393 only taking triangle wave, sin wave is not going? why I don't understand. please give suggestion to the above points. In this picture below, I am referring to this circuit, please tell me what 's wrong in this circuit, when I am taking triangle wave from 555 timer ad providing into the comparator and another signal providing from the generator. View attachment 210902View attachment 210903
 

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Thread Starter

Arijeet

Joined Dec 27, 2019
78
R6 pull-up is too high a value to drive the stray capacitance at that frequency, giving the rounded rise-time.
Reduce its value to about 1.3kΩ.

Note: Never leave CMOS inputs floating as you show for U3.
Connect all unused inputs to ground.
I understand your point. let I explain you everything before you want to conclude anything .i am generating triangle wave from TLC 555 timer, I have also attached pictures shown below, in the real-time practical performed, I have seen triangle wave coming, it looks like a sawtooth wave but it's okay .carrier frequency is above 200 kHz, the output voltage is 2.14 vpp . if you carefully my triangle wave is coming with dc offset(look at arrow ground ref in the scope), now I am giving this signal to the lm393 inverting port, now I am providing audio signal conserving all input common voltage range .it should be less than 2.14 volt, audio frequency 1 Hz to 20 kHz. now when I am providing to the 3rd pin or non-inverting pin in lm393, the output signal is coming in the above picture. I will upload one more picture. , my question is how I can improve square wave, and one more thing still I have connected this lm393 output with hex inverter, I am only connected with 10 k pull up resistor. only . Help me.
 

Thread Starter

Arijeet

Joined Dec 27, 2019
78
In my Lm 393 comparator, my output is not coming proper square wave.picture is shown below.i have described about my circuit. practically
I am using voltage comparator LM393 for comparing two signals, one signal is my reference signal which is a triangle wave, with voltages 2.08 volt generated by 555 timers above 200kHZ giving to the input terminal of inverting side of LM393 and input signal or modulating signal which voltage is less than 2.08 giving from function generator as a sinusoidal signal in the range of 1 Hz to 20kHz in the noninverting side of LM393. My question is when I am providing two signals it should be compared and give a square wave, but LM393 only taking triangle wave, sin wave is not going? why I don't understand. please give suggestion to the above points. In this picture below, I am referring to this circuit, please tell me what 's wrong in this circuit, when I am taking triangle wave from 555 timer ad providing into the comparator and another signal providing from the generator. View attachment 210902View attachment 210903
 

MisterBill2

Joined Jan 23, 2018
7,711
I understand your point. let I explain you everything before you want to conclude anything .i am generating triangle wave from TLC 555 timer, I have also attached pictures shown below, in the real-time practical performed, I have seen triangle wave coming, it looks like a sawtooth wave but it's okay .carrier frequency is above 200 kHz, the output voltage is 2.14 vpp . if you carefully my triangle wave is coming with dc offset(look at arrow ground ref in the scope), now I am giving this signal to the lm393 inverting port, now I am providing audio signal conserving all input common voltage range .it should be less than 2.14 volt, audio frequency 1 Hz to 20 kHz. now when I am providing to the 3rd pin or non-inverting pin in lm393, the output signal is coming in the above picture. I will upload one more picture. , my question is how I can improve square wave, and one more thing still I have connected this lm393 output with hex inverter, I am only connected with 10 k pull up resistor. only . Help me.
Both posts#2and #3 stated that the pull-up resistor for the comparator output is much to high a value. That alone will explain the long rise time and why it is not a nice rectangular wave-shape. And I see the photo of the assembly and no bypass capacitor across the power terminals of the comparator. And still no hysteresis in the comparator and quite long leads on most of the circuit.
Jn addition, comparator switching is better with higher drive levels, and with the voltage divider shown the drive level is not that high.
Has the comparator load resistor value been reduced from the 10K ohms?
AND still, are the other sections of that CMOS gate following the comparator now grounded? Unused CMOS gate inputs MUST be held either low or high or the whole IC will not function as desired.

If the TS is not willing to take good advice it will no longer be offered.
 
Last edited:

Thread Starter

Arijeet

Joined Dec 27, 2019
78
Both posts#2and #3 stated that the pull-up resistor for the comparator output is much to high a value. That alone will explain the long rise time and why it is not a nice rectangular wave-shape. And I see the photo of the assembly and no bypass capacitor across the power terminals of the comparator. And still no hysteresis in the comparator and quite long leads on most of the circuit.
Jn addition, comparator switching is better with higher drive levels,
okay, I got your point. so I will do 3 three things,1- reducing the value of pull up resistor,2- adding a bypass capacitor into the power lines,3-add a 1M resistor connecting with pin 2 and pin 1 (inverting and output ) this point refers the hysteresis .please correct me where I am wrong . and I am going to upload my new results asap. I would like to add, I am not connected to the output of the comparator with hex inverter or any circuit. the circuit only consists of TLC 555, Lm393 only.
 

MisterBill2

Joined Jan 23, 2018
7,711
okay, I got your point. so I will do 3 three things,1- reducing the value of pull up resistor,2- adding a bypass capacitor into the power lines,3-add a 1M resistor connecting with pin 2 and pin 1 (inverting and output ) this point refers the hysteresis .please correct me where I am wrong . and I am going to upload my new results asap.
The feedback resistor goes to the NON-INVERTING input, so that should be correct.

I am heading out to work now so my response will be later.
 

Thread Starter

Arijeet

Joined Dec 27, 2019
78
I have improved muy circuit, now this type of results is coming, is this is a proper signal to give the MOSFET driver2113 ?improvements have occurred in this pictures 1- reducing the value of pull up resistor,2- adding a bypass capacitor into the power lines,3-add a 1M resistor connecting with pin 2 and pin 3 (non inverting and output ) this point refers the hysteresis, please suggest me .what should I do?
 

Audioguru again

Joined Oct 21, 2019
2,380
Your messy long wires on the breadboard are causing the LM393 comparator to oscillate at a high frequency, each time its output goes low.
Why do you use a huge potentiometer with long wires instead of using a trimpot with short leads?
Why are the parts on the breadboard so far apart?
 

Thread Starter

Arijeet

Joined Dec 27, 2019
78
Your messy long wires on the breadboard are causing the LM393 comparator to oscillate at a high frequency, each time its output goes low.
Why do you use a huge potentiometer with long wires instead of using a trimpot with short leads?
Why are the parts on the breadboard so far apart?
should I remove the breadboard wires ?
 

cmartinez

Joined Jan 17, 2007
7,214
Audioguru is right, at those frequencies component placement and trace paths on a PCB becomes very important. I suggest you take a look at this post if you want to learn how to make a proper PCB. The expensive paper cited in that post is no longer necessary, as I discovered that the backing paper of adhesive vinyl film can be also used. With the proper technique of course.
 

Thread Starter

Arijeet

Joined Dec 27, 2019
78
Audioguru is right, at those frequencies component placement and trace paths on a PCB becomes very important. I suggest you take a look at this post if you want to learn how to make a proper PCB. The expensive paper cited in that post is no longer necessary, as I discovered that the backing paper of adhesive vinyl film can be also used. With the proper technique of course.
okay, sir, I will follow your comment and will remove potentiometer and put a trim pot. any other comments you want to say, in a way to improve my circuit.
 
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