24v driven MosFET

[netstranger.nz]

Hi Everyone

I've got a samll problem of driving a MosFET (P or N) in a 24v DC environment.
Before this day, I happily worked in a 12v DC environment (cars). But I have come across several trucks (24v DC) and now industrial automation systems that are 24v DC religiously.
So three things to modify (for a start):
* 5v reg isn't a problem as a lot of switch-mode regulators will take 7 - 40V.
* MosFET drivers aren't a problem as MICROCHIP produces FET drives with 4.5 to 30v supply.
* FETs are a bit of a problem because of their Vgs limit. The highest I could find is 20V max (other characteristics being realistic).

Can you please share your experience and ideas in working with 24V DC

Thanks in advance.

[Ioannis]

P or N?

It is different thing.

About the Microchip drivers, which is the one that is up to 30 Volts?n

Ioannis

[netstranger.nz]

TC4431
TC4432
P and N in one application (to be more general) say for an H bridge

[Ioannis]

I will give you an idea on P driver because I had a similar problem. Needed to drive a P-Mosfet from a PIC and the load was operating on 24V battery (up to 28,5 volts fully charged).

I ended with a small mosfet from PIC output driving a resistive divider to the P-Mosfet,because of the Vgs as you noted.



Ioannis

[netstranger.nz]

Thanks a lot Ioannis for waking me up. I've completely forgotten that often Mosfets do not need much current to switch them on/off. Attached is the oscillogram showing some delay on switch_OFF. The FET is driven by PIC through 10k and 330R respectively.
I've got a question then. In what situation would one need a 3A FET driver. Considering 5/330 = 0.015A does a pretty good job as seen above.

[Ioannis]

I cannot understand how is your circuit. Please attach it to see what you have done.

About the driver FET, the one I select was based on price, availability, size and speed.

Remember that when you try to switch ON the Power mosfet, you try to bring low the gate. The gate is at that moment a capacitor charged at 24 volts and discharged through the small FET and the 470 or 330 resistor.

Also remember that the resistor on my schematic should be at least 1/2 watt because when the small MOSFET is ON, they draw a current of at least 16mA and this leads to power loss of 0.391 Watts!

Ioannis