Three phase inveter ouput issuse with optocouplers islation

[JUN2]

Hi, i am using opto as an isloation between a three phase gate driver circuit and controller(signal generator), but i met a problem that is when i connect for example INH3 and INL3(also the ouputs from opto) the same time from opto board to the driver board,
and when i give INL (low side mosfet switching) signal, the Vgs of low side mosfet shows nothing, but once i unplugged the INH3 connection bwteen driver and opto, the there will be vgs waveform, the whole time i didn't give any siganl to INH3.
Also when i directly give INH or INL signal without the opto islation, the waveform is right, high side and low side mosfets are switching, the problem should not be driver circuit, i tried to use a seprate Vcc power supply, and also tried to seprate INH and INL opto on different pcb board, but the issue still there, i think it might becuase they shared the same ground, however they have to share the same ground of driver, so i just get stucked, anyone could help, thank you so much

 

[KlausST]

Hi,

So the signal path is:
Microcontroller -> cable -> R1 -> IC1 -> ? -> gate driver
And all the signaling is somehow defined by: voltage, current, timing
.. basically that´s all ...


look at your own schematic: do you see
* what microcontroller is used? It´s signal output voltage and/vs current?
* what cable and connectors are used?
* the value of R1?
* the power supply (voltage) to IC1?
* why there is an R9 (what value) in series to the supply of IC1? (I highly doubt that this is accrding datasheet recommendations)
* the power supply decoupling capacitor(s)?
* what is "INH1"
* what gate driver is used? What voltage it is supplied with, if the external connections are according datasheet?

I guess you recognize we really miss a lot of essential informations... ;-)

If you want us to check any IC function and specifications .. please post links to their datasheets (directly at the manufacturer site)
(This makes it more eaysy for us, less time consuming, avoids misunderstandings ... and thus gives faster and more accurate feedback for you.)

***
Regardless ... whether informations are missing.

What did you do so far? (By telling us the results, we see your effort, we see what possible problems can already be excluded. No need for wild guessing)
One appoach should be to trace the signal ... according the above mentioned signal path:
* does the microcontroller output the expected signal? ... according voltage level and timing..
* then the cable input ... and output ..
* the resistor input and output ..
... step by step ...
...
for this you need to have the datasheets by hand . . to know the specified output levels .. as well as the specified input thresholds

.. this - at least - is how I would do the debugging

Klaus