# Help with mosfet and resistors

• eyore@raat
In summary: Hz.In summary, you would need a 100ohm resistor in series with the gate of the mosfet to turn it on, and a 30k resistor in parallel with the gate to discharge it when the trigger is pulled.
eyore@raat
Hi I am trying to figure out how to determine the size of the resistors I need to put in line of the gate wire to turn on and off the mosfet in a circuit for an airsoft gun
I have several mosfets laying around the 1 I want to use is a 50a 100v
that said what size resistors do I need to put in line for the gate 100ohm ?watt and what watt do I need to use for the discharge a 30kohm ? watt
like they have in this schematic

http://www.airsoftmechanics.com/home/content/view/23/30/1/6/

any help will be greatly appreciated

Last edited by a moderator:
The wattage of the resistor can be computed from the two equations E=IR and P=EI.
In this case E would be your battery voltage.
In selecting the resistor the common practice is to double the computed wattage to allow for environmental effects.

first I would like to say thanks for replying
next is there a way you could explain that in a more simple way I am just starting out in electronics and know very little I need it in layman's terms please

R = Resistance
I = Current
E = Voltage (or EMF)
P = Power (or Watts)

You probably don't know the current.
The battery voltage you can get from the battery.
The resistance you stated.

A little algebra and the two equations will let you solve this without knowing the current.

The best way to go about it is to see the gate waveform on an oscilloscope. Then you tweak the value of 100ohm and see if any ringing occurs at all. The 30k discharge resistor depends on the gate capacitance and how quickly you want that to be discharged (A rough value is 1600pF but it varies from MOSFET to MOSFET so please look up the datasheet). Time constant= RC.

Not that I actually worked this out, but I suspect that the most current will flow when the trigger switch is pushed putting the battery voltage across the 30k resistor.
The gate charge works out to < 20nJoules and the repetition rate is essentially 0.

## 1. What is a MOSFET?

A MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) is a type of transistor that is commonly used in electronic circuits. It is used to control the flow of current between the source and drain terminals by applying a voltage to the gate terminal.

## 2. How does a MOSFET work?

A MOSFET works by using an electric field created by the voltage applied to the gate terminal to control the flow of current between the source and drain terminals. The voltage applied to the gate terminal determines the resistance of the MOSFET and thus, the amount of current that can flow through it.

## 3. What is the function of a resistor in a MOSFET circuit?

A resistor is used in a MOSFET circuit to limit the amount of current that can flow through the circuit. This is important because too much current can damage the MOSFET and other components in the circuit.

## 4. How do I choose the right resistor for my MOSFET circuit?

The value of the resistor you choose will depend on the voltage and current requirements of your circuit. You can use Ohm's law (V=IR) to calculate the resistance needed for your circuit. It is also important to consider the power rating of the resistor to ensure it can handle the amount of current flowing through it.

## 5. What are the common applications of MOSFET and resistors?

MOSFETs and resistors are commonly used in a wide range of electronic devices, including power supplies, amplifiers, and digital circuits. They are also commonly used in switching circuits, motor control, and LED drivers.

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