question about multisim

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karas

Joined Sep 8, 2011
208
can some one help me to do simulation for optocoupler (hcpl3180) in multisim i can not find any optocoupler in my multisim ,
second question how can i do simulation for PWM (I HAVE FET AND I NEED TO BE ABLE TO VARY THE PULSE WIDTH )
 

crutschow

Joined Mar 14, 2008
23,508
can some one help me to do simulation for optocoupler (hcpl3180) in multisim i can not find any optocoupler in my multisim ,
second question how can i do simulation for PWM (I HAVE FET AND I NEED TO BE ABLE TO VARY THE PULSE WIDTH )
Optocoupler models are hard to find. You might Google "optocoupler spice models" and see if you see anything appropriate.

You can generate a PWM signal using the controlled_one_shot source.
 

praondevou

Joined Jul 9, 2011
2,942
There is nothing similar to the HCPL-3180 in MS.
I've personally used it and it's use is really straightforward.
Just make sure you use it according to the datasheet specifications when you finally build your circuit,e.g with a proper bypass capacitor and the right Rgates or use oversized Mosfets/Igbts and you will not run into any problems. But these problems (mainly layout) you wouldn't see in the sim anyway.

For simulation purposes I would either not even bother to include it or build a small block, just take a resistor, apply the PWM to it (to simulate the LED forward current), then drive directly the FET with it.
If you only want to change pulse width, you can take a simple clock voltage and change it's duty cycle. Of course this doesn't work during simulation.You'll have to restart it..

Of course, what I just wrote only works if you use the clock voltage source, since it has zero internal resistance. You find it under signal voltages sources.

If the PWM comes from another circuit of yours whose output impedance I don't know, you could try to simulate the driver with a handmade buffer made out of p-mosfets and n-mosfets, but this probably introduces a bigger propagation delay than the HCPL 3180 has.

Maybe you should post your diagram so other people can also help you out with LTspice etc. There are highspeed optocouplers that could maybe adapted to your needs with a power driver stage after it to simulate the HCPL.
 
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