audioguru2
- Apr 6, 2004
- 12,026
- Joined
- Apr 6, 2004
- Messages
- 12,026
Why not look at a datasheet? Like for an IRF540 Mosfet:
1) The gate threshold voltage to cause the Mosfet to conduct only 250uA is between 2V to 4V.
2) It conducts best (33A) with a gate voltage of 10V.
3) Its max gate voltage is 20V.
It is a Mosfet. Mosfets don't have gate current.
BUT, its gate has a high capacitance that needs a fairly high current to charge quickly so that the Mosfet can turn on quickly, so that it doesn't heat up much when it is switching.
I go to www.datasheetarchive.com for datasheets.
1) The gate threshold voltage to cause the Mosfet to conduct only 250uA is between 2V to 4V.
2) It conducts best (33A) with a gate voltage of 10V.
3) Its max gate voltage is 20V.
It is a Mosfet. Mosfets don't have gate current.
BUT, its gate has a high capacitance that needs a fairly high current to charge quickly so that the Mosfet can turn on quickly, so that it doesn't heat up much when it is switching.
I go to www.datasheetarchive.com for datasheets.
A bit more clarification on a few points..............
Gate capacitance isn't the "important" number... "total gate charge" is what will determine how much current is needed to switch a FET on in a particular amount of time given the drain source voltage. Typically, the lowest Rds on is had at the highest Vgs (max channel enhancement), but may not be, and in most cases isn't, the optimum operating point unless it's a static application (i.e. DC switch). Unless prolonged periods of time are spent in the ohmic region, switching losses in a power MOSFET aren't that big when compared to Rds on losses (I^2R). Assuming adequate current is available, optimal gate drive voltage levels will vary with switching frequency.
Gate capacitance isn't the "important" number... "total gate charge" is what will determine how much current is needed to switch a FET on in a particular amount of time given the drain source voltage. Typically, the lowest Rds on is had at the highest Vgs (max channel enhancement), but may not be, and in most cases isn't, the optimum operating point unless it's a static application (i.e. DC switch). Unless prolonged periods of time are spent in the ohmic region, switching losses in a power MOSFET aren't that big when compared to Rds on losses (I^2R). Assuming adequate current is available, optimal gate drive voltage levels will vary with switching frequency.
