Problem with optocupled pwm signals SOLVED

[tronicgr]

I used these values (1.5k) after testing in real hardware. I used 4.7k potentiometers for the input and output and I found that I was getting perfect waveform shape with 1.5k for both input-output stages. These values allow equal cut-off range for both low and high range (about 10%). Then I normalize this signal with Schmitt trigger (74hc08) to allow proper switching for the mosfets.

Have a look in the waveforms here: http://www.x-sim.de/forum/viewtopic.php?f=39&t=132&start=20#p978


Sometimes you have to have in consideration the type of the signal you want to transfer instead of just using the maximum recommended values from the datasheet.

Thanos

[prilad]

Sometimes you have to have in consideration the type of the signal you want to transfer instead of just using the maximum recommended values from the datasheet.

Oh, yes, I absolutely agree with you.
What can you advise to solve the eldeejay's problem?

Regards,
Ale

[eldeejay]

Hi all, sorry for the delay in replying, work and my family did not leave much free time

I carefully studied your pictures and saw that you use 4n25 optocoupler. I think you have Thanos isolator schematics.

Hi Prilad, i´m using optocuplers 4n26, (4n25 and 4n26 are equal) and i was using Rled=100 ohm. I'm not using any of tronic optoisolators scheme.

My Optocoupler Solution Explanation xD:
I've done enough evidence about the problem that I have described and solved using optocouplers smith trigger. First I implemented one of the signs of the optocoupler SFH6705 H bridge (open collector output) and the output signal is perfect. But this model has a drawback, the emitter of the output transistor is referenced to ground the optocoupler and that ground must be referenced to the motor supply / H bridge, this forces the engine operating voltage never exceed 15VDC .
That is why I changed the model optocoupler SFH6732 or SFH6731. http://www.vishay.com/docs/83685/sfh6731.pdf
It is a high speed optocoupler 2ch that operates from 4.5 V up to 15V. Using 14Vdc for this optocoupler, its output will always be about 13 - 14V and ensuring that exceeds Mosfet VGS = 10V and being able to use motor voltage / H bridge from 12 to 55 VDC, I perish important h bridge allows to use a large margin voltage. With only 2 components i´ve optocoupled control signals.






The "Optolink" tronic use 6 optocouplers + 12 resistors + 74HC14; optocoupler all control signals and PWM, in total 6, after integrates signals to smith trigger inverters 74HC14 and finally used 74HC08 to AND the control signals applied to the H bridge.

I simply put my 74HC08 outputs directly into the SFH6732 and applied them to the H bridge. This is my diference.

Thanks very much for your help and remain at your disposal
Regards

[RafBR]

Hello Mr Eldeejay,
I was looking for one solution just like yours
as you can see here:
viewtopic.php?f=43&t=68&start=30

The problem was that slotted optocouplers are slower, right? Then we would have to rectify the pwm waves...

Can you show how would be the wiring for the sfh6732?

My regards!
Rafael.

[eldeejay]

Can you show how would be the wiring for the sfh6732?

Hi RafBR, of course. Wait a little time, I have to draw it.
Reagards xD