Hello all , I have made an optocoupler relay PCB.. that I'm using with my stm32 development board.. that relay power at 5V and triggered at 3.3V .. sometimes my controller board give less voltage like 3.2 or 3.21 at that time it's not triggering can someone tell me what's going on or help me ..

 

hiJ;
Please post a diagram with component values.
E

 

When you post your schematic, make sure that each component has a unique reference designator (R1, R2, etc.) and the component's value. Without this information, discussing how the circuit functions is very difficult.

ak

 

can someone tell me what's going on or help me

Not without more information. What is the part number for the relay and where's the schematic?

Your posts would be easier to read (meaning you're more likely to get responses) if you used proper grammar (capitalization, paragraphs, and sentence terminators).

 

Most Relay manufacturers will provide "Must-Break" and "Must-Make" Voltages,
unless, of course, You got your Relay from China.
.
.
.

 

Since few of us are clairvoyant, you will need to post a schematic of what you, if you want help.

 

Of the relays I've used, pick-up voltages of 70-80% of the nominal coil voltage were specified. 70% required selected devices.

You're below 65%.