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Help with MOSFETs

Help with MOSFETs

Help with MOSFETs

(OP)
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

RE: Help with MOSFETs

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

TTFN



RE: Help with MOSFETs

(OP)
Sorry smile 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

RE: Help with MOSFETs

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

Keith Cress
Flamin Systems, Inc.- <http://www.flaminsystems.com>

RE: Help with MOSFETs

Excess capacitance on the gate?

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

RE: Help with MOSFETs

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/>

RE: Help with MOSFETs

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?

RE: Help with MOSFETs

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.  

RE: Help with MOSFETs

(OP)
Thanks for the help guys!

swb1

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