Mosfet driver circuit

Thread Starter

Sweetest Fruit

Joined Jan 10, 2023
So I designed a circuit to drive mosfets through which high powered devices will be connected to.

These devices are mainly a led bar of (24 V, 3 A), a high powered relays (24 V, 30 A) and a dc motor (12 V, 30 A) in my lab.

The low side gate driver I choose is the UCC27517DBVT and it will be controlled by a microcontroller such as the arduino. The LED bar will be driven with pwm and the relay as a switch.

One of my concerns was the choice of mosfet I made, knowing that the one selected only dissipates 26 W and that the vgs optimal for a low RDS On is 10V and full current of ID = 40 A.

Basically I'd like to get feedback to know if these circuits need to be modified or if they are over engineered for the purpose of device control and flexibility.

Thanks !



Joined Mar 10, 2019
Your MOSFET is a logic level device, it will provide a RDSon of 7 milliohms at 4,.5V on the gate. There may not be a need for the "driver". Also, the TVS SMAJ6V5 (I assume SMAJ6.5) will clip any voltage over 7V (approx.), so why have a driver trying to feed 10V to 12V?
Regardless of the gate voltage (4.5V or 10V), you will still need a reasonable heatsink on the 30A device to dissipate the heat.


Joined Jan 17, 2007
You almost certainly do not need a driver for the upper circuit. On that side you can do away with the UCC27517 driver, and R1. Also, R2 can be 100K instead, so as to consume less current when driving the relay.

For the lower part (the LED bar circuit) you might need a driver depending on the switching frequency. In which case R3 should be of a much lower value (about 10 ohms) because that part is there to prevent "ringing" at the Fet's gate while applying PWM. And I'd suggest you changed R4 to 10K, which is a much more common commercial value. I'm guessing C1 is there to smooth the voltage across the LED bar a bit while it's being PWM'd, so you might want to experiment with its value. And placing a TVS or Zener diode across the LED bar (such as D2, which is placed across the relay coil in the upper side of the circuit) would add protection to X5.


Joined Aug 7, 2020
R1 and R3 completely spoil the effects of the driver. The driver wants to drive a large current into the gate to charge it up quickly to ensure a rapid on-off transition, and R1 and R3 prevent it from happening, making it as slow as if there were no driver.