need help regarding MOSFET.

[niks]

regardingmosfet

Hi
Im using BSP88. Vds = 2.4,Vgs=2.4.When there is low to high transition at the GATE, im getting sudden shoot of 1.5 V at source side. It'll be there for 10uS then it settles down. Why its behaving like this? And whats the solution?


O Vcc = 2.4
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> 470K
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--|<- BSP88
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> 6.8K
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Regards
~niks~

 

[sutapanaki]

Can you clarify a bit. It is not very obvious from your drawing how the gate is connected. Is it driven separately or it is connected to the drain - you say both drain and gate are at 2.4v? Do you also mean that Vcc can simply have a value somewhere in the range you specified or it is also changing - like a signal?

 

[flatulent]

gate-source capacitance

This looks like the gate-soruce capacitance is putting part of the gate drive on the source. Try slowing down the gate drive rise and fall times to see if it goes away.

 

[niks]

Actually the input will be at 2.4 V when Gate will be enabled.

 

[aaaaa]

It is the current that flows into the gate to charge the G-S capacitor. The current flows into the G, than capacitivly coupled to S, through your S resistor and back. You can calculate required Q from GS capacity of your MOSFET and voltage (2,4V in your case).

 

[superluminal]

can you draw it with any schematic program ? & please tell us if these values are from simulation or from your testbench

 

[jodokus]

I agree with the others that this must be caused by the g-s capacitance. Try lowering your resistance values or add a resistor in series with the gate to minimize this phenomenon. I don't know the rest of your schematic but maybe you are better off with a bipolar transistor here.