Problem when measure square wave and Charge & Discharge

Thread Starter

Sakamoto21

Joined Jan 20, 2023
9
Please help me, I got problem.
From circuit diagram
Target : I want to make square wave on Vout (Period =18 sec on :8 sec off: 10 sec)
I have problem when I use scope to measure triangle and Vout , I have followed target. But when I use scope to measure Vout only, time Period and time on reduce. it's not followed target.
I don't understand.
Q: why measure triangle signal and no measure, it's too difference.
* Actual I use op-amp: NJM2904C.


1674536768442.png

Simulate Vout
Period: 17.79 sec
on: 8.1 sec

1674540841348.png


Actual (No measure triangle)
Period : 16.67 sec
on 5.916 sec

1674541138399.png
Actual (measure triangle)
Period: 18.295 sec
on: 7.689 sec

1674541322756.png
***Actual is same sample and same parameter.o_O
 

Attachments

Thread Starter

Sakamoto21

Joined Jan 20, 2023
9
h S21.
This is what I see on LTS.
E
I have deleted the 1Sec Time step in .tran
I try make actual sample and measure on scope.
When I measure triangle point and Vout -> period,on time ,off time follow target.But
When I measure Vout only -> period,on time reduce.
Did you know cause that. I don't know why occur that

My Hypothesis :
1. I think about select op-amp ?
2. frequency on scope ?
 

ericgibbs

Joined Jan 29, 2010
18,767
Hi S21.
The scope probe of say 1meg or 10meg resistance on Triangle node loads that pin and causes a change in frequency.
Look at this sim.

E
EG57_ 490.png
 

ericgibbs

Joined Jan 29, 2010
18,767
Hi,
He says,
Q: why measure triangle signal and no measure, it's too difference.
* Actual I use op-amp: NJM2904C.

This simple question is pretty clear to me.

IF he asks for alternative idea's, no problem, but let's try to answer his original query first,
E
 
Top