Opamp triggering with optocoupler problem

Thread Starter

Ahmet Pehlivan

Joined Oct 16, 2022
In this circuit, if i connect the pwm (mcu output) to the pwm_output directly ( without optocouper) everything is fine but whenever i use optocoupler opamp is never triggering. Can anyone help ?
WhatsApp Görsel 2023-07-20 saat 13.01.21.jpg


Joined Dec 13, 2021
the op amp input is "high impedance"
so if you connect the transistor part of the opto to the op amp input
"zero" or about that current flows,
as @DickCappels says, put resistors on the output of the opto, and you give some where for the current to flow, so the opto can control the current..


Joined Mar 14, 2008
The opto output pulls the op amp input signal up to 5V, but there is nothing to pull it down to 0V.
When the opto is off the output is an open circuit, and an open circuit is not necessarily 0V.
With the characteristics of that op amp input (PNP transistors) it likely just stays near 5V.