Mosfet gate charge with no voltage across D-S

In summary, the conversation discusses whether a mosfet has any gate charge when there is no voltage applied across D-S. The speaker's intuition suggests that there should not be any gate charge, but they are unsure due to the mosfet being a semiconductor. They are asking this question in order to test for a fault in their mosfet driving circuit and determine if the same current is needed to drive the mosfets without them being attached to voltage. It is noted that there is still a small capacitance present, so applying a gate voltage will still lead to a gate charge.
  • #1
Salvador
505
70
Hi , I would like to find out does a mosfet have any gate charge if there is no voltage applied across D-S or no ?
my intuition tells me that there shouldn't be any gate chrge as there is no voltage on the " second plate" to attract that charge like would be the case in a capacitor, although mosfte being a semiconductor maybe because its current carrying channel is doped with current carriers it responds to gate signal even with no voltage across D-S, ?

I am asking this because I need to test for a fault in my mosfet driving circuit but I need to know whether it has the same current need driving the mosfets without them being attached to voltage or no?otherwise i couldn;t fully replicate working condition and also determine the fault.
 
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  • #2
You still have a small capacitance, so applying a gate voltage will lead to a gate charge.
 

FAQ: Mosfet gate charge with no voltage across D-S

1. What is the purpose of measuring Mosfet gate charge with no voltage across D-S?

The purpose of measuring Mosfet gate charge with no voltage across D-S is to determine the amount of charge required to fully turn on the Mosfet. This is important for understanding the switching behavior and efficiency of the Mosfet in different circuit applications.

2. How is Mosfet gate charge measured with no voltage across D-S?

Mosfet gate charge is typically measured by applying a small voltage to the gate terminal and monitoring the resulting current flow. By measuring the change in current over time, the total gate charge can be calculated. This measurement is done with no voltage across the drain-source terminals to isolate the effect of the gate on the Mosfet.

3. What is the significance of no voltage across D-S in Mosfet gate charge measurement?

No voltage across D-S is significant because it allows for a more accurate measurement of the gate charge. By isolating the gate, any parasitic effects from the drain-source voltage are eliminated, providing a more precise measurement of the gate charge.

4. How does Mosfet gate charge with no voltage across D-S affect circuit performance?

The gate charge of a Mosfet with no voltage across D-S can significantly impact circuit performance. A higher gate charge means it takes longer to fully turn on the Mosfet, which can result in slower switching speeds and higher power dissipation. It is important to select a Mosfet with a suitable gate charge for the intended circuit application.

5. Are there any limitations to measuring Mosfet gate charge with no voltage across D-S?

There are a few limitations to measuring Mosfet gate charge with no voltage across D-S. One limitation is that the measurement may not accurately reflect the gate charge in a real circuit, as there may be parasitic effects from other components present. Additionally, different measurement methods may yield slightly different results, so it is important to use a consistent method for comparison.

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