Kral
Joined: 28 Mar 2005
Posts: 1182
Helped: 187
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 26 May 2005 16:21 Re: Please, help trying to find a design to do that...... |
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There are several things to consider:
1
The gate-source voltage magnitude must be greater than the rated Vgs(on) rating of the FET. The amount that you need to exceed the Vgs(on) rating is approximately equal to: DeltaV = Iload/gfs, where gfs is the minimumum rated forward transconductance of the FET. Example:
. Vgs(on) = -2V
. Iload = 10 Amperes
. gfs = 5
Then
. Vgs must be at least -2 - 10/5 = -4V.
2
The saturation current (current where the drain current vs Vgs curve flattens out) must be greater than the maximum load current. Look at the data sheet curves to determine this.
3
Since you are working with positive source and load voltages, it would be easier to design a switching circuit that uses NMOS FETs. That way the Vgs for the "On" state would be positive.
Regards,
Jon
Added after 1 minutes:
There are several things to consider:
1
The gate-source voltage magnitude must be greater than the rated Vgs(on) rating of the FET. The amount that you need to exceed the Vgs(on) rating is approximately equal to: DeltaV = Iload/gfs, where gfs is the minimumum rated forward transconductance of the FET. Example:
. Vgs(on) = -2V
. Iload = 10 Amperes
. gfs = 5
Then
. Vgs must be at least -2 - 10/50 = -4V.
2
The saturation current (current where the drain current vs Vgs flattens out) must be greater than the maximum load current.
.
Since you are working with positive source and load voltages, it might be easier to design a switching circuit that uses NMOS FETs. That way the Vgs would be positive.
Regards,
Jon
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