Help with MOSFETs

[swb1]

Hi,

Using power Mosfet MGSF1N03LT1 (On Semiconductor), the FET takes a long time to turn off (1.2 microsecs.). Why is this?? I need for it to turn off quicker. Any suggestions on different Mosfets that will turn off quicker with the same characteristics as the On Semiconductor part??

Thanks,

swb1

 

[IRstuff]

Using your non-information, my brain can't turn on.

TTFN

 

[swb1]

Sorry the data sheet says that the turn off time Td(off) is typically 16 ns with Vdd = 15Vdc, Id = 1.0 Adc, and RL = 50 Ohms. In my circuit, Vdd = 6Vdc, Id = 30mA, and RL = 100 Ohms and it takes 1.2 microsecs to turn off. Why is this??

swb1

 

[itsmoked]

Like what are you driving it with??? What is the entire drive circuit?

Keith Cress
Flamin Systems, Inc.- <

http://www.flaminsystems.com>

 

[analogkid2digitalman]

Excess capacitance on the gate?

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
"It's the questions that drive us"
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 

[itsmoked]

My questions still stand.

Keith Cress
Flamin Systems, Inc.- <

http://www.flaminsystems.com>

 

[nbucska]

Any mosfet has large gate C -- sometimes many nF-s.
You need hi-current driver to drive the gate fast
enough. If the Rout is high, the R*C time constant
will slow it down.


Plesae read FAQ240-1032
WEB: <

http://geocities.com/nbucska/>

 

[zeitghost]

MOSFET gate drivers typically source & sink half an amp or more to turn on & turn off fast.

Repeating the above question... what's your drive circuit like?

 

[MrBananas]

Ditto with the above comments on drive circuitry.

FETs need to establish an electric field to control current flow.

As you may remember from physics, the voltage on a capacitor doesn't change instantly, you have to transfer charge for the voltage to change. The more current your driver can source or sink into/out of the gate, the faster the voltage will change on the gate and the faster the FET will turn on/off. There are other parasitic capacitances in the FET as well, but the gate-to-source capacitance is usually the one that lengthens switching time considerably.

 

[swb1]

Thanks for the help guys!

swb1