Hi, i designed Optocoupler, however, the output voltage is not stable at all, i use a waveform generator give 3.3Vpp and 50%duty,25khz square waveform signal, the ouput side is shown in imagie, here is also the circuit of opto, the input side i use a 120 ohm res to limit the current, calculated by giving 3.3V input voltage, and output side i use 1k ohm pull up res, the ouput vcc supply is 15V, anyone could help, thank you in advance,

 

Something doesn't add up. If Vcc=15V, how would your first scope pic show a signal value of 27.9V (top of pic) and an RMS value of 19.5V? What is happening at the Vee node?

 

The first picture looks like the scope probe ground is not connected.

 

Most likely the scope ground was connected to the opposite, isolated ground.

 

Something doesn't add up. If Vcc=15V, how would your first scope pic show a signal value of 27.9V (top of pic) and an RMS value of 19.5V? What is happening at the Vee node?

thank you for replying, i made a stupid mistake that i should connect the probe ground to the ouput side of opto ground, after that it is right

 

Most likely the scope ground was connected to the opposite, isolated ground.

Thank you for replying, yes you are right, i connect the wrong ground

 

The first picture looks like the scope probe ground is not connected.

Thank you for replying, i connected the wrong ground, now it works

 

now it works

We like knowing. We get paid in thanks not dollars, pounds, yen, rupees, etc. lol

 

I echo what Ron mentioned.
A polite reply is always valuable.