I have a design that requires a PWM input to be isolated from the output. The input is driven from a mcu (3.3V), the output has a 15V DC power supply and requires the PWM to be 4V.
I have modelled this in LT Spice with a basic 4N25 and can get the concept to work OK at 1kHz. I require resolution of 40 discrete values for the PWM so 6 bit accuracy is fine. Resistors R2/R3 drop the supply voltage down to the required 4V output.
Now the 4N25 is a pretty basic low speed part which won't work as I'm looking to get the PWM frequency up to a minimum of 100kHz.
At my required resolution of 40 discrete values this would required a turn on/turn off time of 250nS.
I've looked at parts with active outputs to get the speed up, the constraint being the 15V DC power supply (most active devices run to ~6V). I've found two parts that run to 30V supply:
- Vishay VOM453, which has an open collector output so could be plugged into my circuit. The speed though is a bit slow with turn off and turn on running to 1,000 nS.
- Broadcom ACPL-M484, which has a push/pull totem pole output. I think this will require an additional N channel driver for my P channel output but has faster turn on/turn off times (~200nS)
I'm having trouble finding LT Spice compatible models for these two parts.
How would I modify an existing model ?
I have modelled this in LT Spice with a basic 4N25 and can get the concept to work OK at 1kHz. I require resolution of 40 discrete values for the PWM so 6 bit accuracy is fine. Resistors R2/R3 drop the supply voltage down to the required 4V output.
Now the 4N25 is a pretty basic low speed part which won't work as I'm looking to get the PWM frequency up to a minimum of 100kHz.
At my required resolution of 40 discrete values this would required a turn on/turn off time of 250nS.
I've looked at parts with active outputs to get the speed up, the constraint being the 15V DC power supply (most active devices run to ~6V). I've found two parts that run to 30V supply:
- Vishay VOM453, which has an open collector output so could be plugged into my circuit. The speed though is a bit slow with turn off and turn on running to 1,000 nS.
- Broadcom ACPL-M484, which has a push/pull totem pole output. I think this will require an additional N channel driver for my P channel output but has faster turn on/turn off times (~200nS)
I'm having trouble finding LT Spice compatible models for these two parts.
How would I modify an existing model ?