Hi
I want to use a MOSFET transistor as a switch to drive a motor..
My question is: Should I connect a resistance to the gate of the MOSFET, or not ??
As I know, The MOSFET has an isolated gate. But I have seen many designes with a resistance connected to the gate of the MOSFET!!!!
any comment
The gate resistance is used to slow down switch operation to a defined di/dt or du/dt rate. Also unwanted RF oscillations during switching are reduced. Basically increasing the gate resistor gives slower current and voltage transition at the output, less overvoltage but increased switching losses. Gate resistor dimensioning depends on MOSFET size, respectively gs and gd capacitances. Could be a few ohms up to several 100 ohms.
A resistor in series with the gate of a Mosfet must be mounted very close to the gate pin. It stops the Mosfet from oscillating at a very high frequency which might make it too hot.
If you don't connect a resistor in series with the gate of a Mosfet right at the gate pin then it can oscillate at a high frequency which might cause it to over-heat.
Ok..I will use IRFZ44 MOSFET transistor to control a 3A DC motor
I will control the speed of the motor using a pulse width modulation signal (PWM) with a frequency up to 1 KHz
Should I connect a resistance or not???
If I should..What is the optimum value of the resistor??
The datasheet of IRFZ44 **broken link removed**
Audioguru said:
A resistor in series with the gate of a Mosfet must be mounted very close to the gate pin. It stops the Mosfet from oscillating at a very high frequency which might make it too hot.
I klooked in Google at Mosfet Gate resistor.
Fairchild have a switching power supply (pretty high frequency) and they say to use 4.7 ohms in series with each gate. They show the switching time slowing down with a gate resistor of 20 ohms.
Fairchild says that a mosfet can oscillate at up to 100MHz and overheat if it doesn't have a series gate resistor.
Your PWM is very slow so a gate resistor of 10 ohms to 68 ohms will be fine.