Solving MOSFET Issues | 180 Ohm Resistor

In summary, MOSFET issues can be solved by using a 180 ohm resistor as a gate pull-down resistor. This helps to prevent the MOSFET from turning on unintentionally and causing issues such as overheating or overloading the circuit. The resistor helps to stabilize the voltage and current in the circuit, ensuring proper functioning of the MOSFET. Additionally, using a higher resistance value can also help to reduce power consumption and improve overall efficiency. Overall, using a 180 ohm resistor is an effective solution for addressing MOSFET issues and ensuring proper operation of electronic circuits.
  • #1
Raisintoe
23
2
I am new to using MOSFET transistors as load switches. Here, I am trying to trigger the P-channel MOSFET to run a current through the 180 ohm resistor. I can not figure out what I am doing wrong. It is supposed to turn on for a small moment (at the zero-crossing moment of the AC phase), then turn back off.
Opto with MOSFET.jpg
 
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  • #2
Your circuit turns on the PMOS at all times except for a small moment (at the zero-crossing moment of the AC phase).
 
  • #3
Svein said:
Your circuit turns on the PMOS at all times except for a small moment (at the zero-crossing moment of the AC phase).

I know it does, but why is it doing that? It is a p-channel MOSFET, why doesn't it turn on when a positive voltage is present? Also, when it does turn on, it has a very small current, (240uA in this LTSpice simulation).
 
  • #4
Raisintoe said:
It is a p-channel MOSFET, why doesn't it turn on when a positive voltage is present?
A p-channel MOSFET turns on when the gate is negative relative to the source. You need to invert the driving signal.
 
  • #5
OK, that's confusing. My next question is, why is the current so small? What do I have to do to increase the current?
 
  • #6
Raisintoe said:
OK, that's confusing. My next question is, why is the current so small? What do I have to do to increase the current?
I do not think the optocoupler is able to drive the PMOS gate as far down as necessary. You need to amplify and invert the output of the optocoupler.
 
  • #7
Svein said:
I do not think the optocoupler is able to drive the PMOS gate as far down as necessary. You need to amplify and invert the output of the optocoupler.

Hmmm, I tied the gate directly to ground, and that didn't change the current through the 180 ohm resistor. I finally get the proper current (27.8mA) when I set the gate to negative 1 million volts!
 
  • #9
It could be the gate threshold for the PMOS is too high. Try setting V2 to 10V and ground the gate.
 
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FAQ: Solving MOSFET Issues | 180 Ohm Resistor

1. What is a MOSFET and why is it important?

A MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) is a type of transistor that is commonly used in electronic devices. It acts as a switch to control the flow of electrical current and is important because it allows for efficient and precise control of electronic circuits.

2. What are some common issues that can arise with MOSFETs?

Some common issues that can arise with MOSFETs include overheating, breakdown due to excessive voltage, and short circuits. These issues can cause the MOSFET to fail and disrupt the proper functioning of the electronic device.

3. How can an 180 Ohm resistor help solve MOSFET issues?

An 180 Ohm resistor can help solve MOSFET issues by limiting the amount of current flowing through the MOSFET. This can prevent overheating and protect the MOSFET from damage. Additionally, the resistor can act as a buffer to reduce the effects of voltage spikes, helping to prolong the lifespan of the MOSFET.

4. What are some other methods for solving MOSFET issues?

Other methods for solving MOSFET issues include adding heat sinks, using a higher voltage MOSFET, and implementing proper circuit design and layout techniques. It is also important to ensure that the MOSFET is not being overdriven and to properly test and troubleshoot the circuit.

5. Can MOSFET issues be prevented?

While it is impossible to completely prevent MOSFET issues, proper circuit design, layout, and testing can help minimize the chances of encountering problems. Additionally, using high-quality components and implementing safety measures such as fuses can also help prevent MOSFET issues.

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