Hello,
I am searching for a suitable optocoupler for driving the circuit shown in the attachment.
The MOSFET is IRLB3036GPbF. I know its different from the diagram.
This MOSFET has awesome characteristics. Low RdsON, 60V, 380W dissipation, 195A...
The current that comes from the battery and cap is 110A. The heat loss in the resistors is of no concern here.
My question is this: what is a suitable and inexpensive optocoupler for driving both of these MOSFETs?
Note: supply voltage for optocoupler can be 5V, 8V, or 12V. The opto is driven with a microcontroller PWM pin at 1kHz frequency (I probably need resistor there too).
Thank you,
My question is this: what is a suitable and inexpensive optocoupler for driving both of these MOSFETs?
No, and most standard optocouplers are not an appropriate device to control power MOSFETS without additional circuitry. A MOSFET gate is like a capacitor that must be actively charged to turn on and active discharged to turn off the gate. Your opto output when turned off is just allowing the mosfet gates to float and not be driven to a off condition. Also significant current drive is required to be able to switch the mosfets on and off as fast as possible to keep switching losses and heat dissipation as low as possible. So the device that is driving the mosfets gates need to have significant source and sink current capacity, which simple optoisolators can't provide. So in a case like your application where you wish to switch high current you need to use a purpose designed 'mosfet gate driver' IC between the optoisolator and the mosfet gates.
Lefty
Hi Lefty,
Thank you for your response.
If the gates are gonna float, is it possible to have a resistor from gates to ground (What value is ok for fast switching?)
Also could you recommend some part numbers for MOSFET drivers for this application.
Thanks
FardinB:
Hi Lefty,
Thank you for your response.
If the gates are gonna float, is it possible to have a resistor from gates to ground (What value is ok for fast switching?)
Also could you recommend some part numbers for MOSFET drivers for this application.
Thanks
Yes, pull-down resistor will turn off the mosfets eventually, but at a speed determined by the R/C time constant of the resistor value and the sum of the two gate capacitance values, a very slow and dangerious way to try and turn off two high current MOSFETS, they most likely will blow up the first time they are commanded to turn off with a full drain current load. To select the 'best' gate driver is a matter of matching the datasheet specs of the gate driver and the gate capacitance values of your mosfets and the switching speeds you want, which in your case due to high current loads, to be as fast as the mosfets will allow. Best to just start learning about gate drivers and mosfets in high current applications, it's not a application to jump into with learning the hazards and solutions needed.
Lefty
