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how we can measure rds by depth of saturation

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phanikiran

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what is the relation between the Mos Drain to source resistance (saturation region rds) and depth of saturation? can we get high rds by setting small vds ?
 

The datasheet of most Mosfets shows it conducting a high current when Vgs is high and conducting a low current when Vgs is low. But each Mosfet is a little different and the resistance between drain and source is affected by the temperature and by the Vds. It becomes a current source or sink.
 

phanikiran said:
can we get high rds by setting small vds ?
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Yes you can, but the off to on transition is fairly abrupt, as mentioned above it is subject to drain voltage and temperature, which makes it rather unstable, and slightly different from mosfet to mosfet.

Its one reason why you never see mosfets used in audio power amplifiers, they are much better suited to on off switching.

If you wish to work in the high resistance region, junction fets are much more easy to use and more user friendly.
 

Warpspeed said:
Its one reason why you never see mosfets used in audio power amplifiers, they are much better suited to on off switching.
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Some manufacturers and some audiophools do have audio amplifiers that use Mosfets. The negative feedback adjusts their operating point the same as negative feedback adjusts the operating point of ordinary transistors.
 

Audioguru said:
The datasheet of most Mosfets shows it conducting a high current when Vgs is high and conducting a low current when Vgs is low. But each Mosfet is a little different and the resistance between drain and source is affected by the temperature and by the Vds. It becomes a current source or sink.
Click to expand...

The Rds(on) can be used in Triode zone as well in Saturation zone ? Or just use it always ?
 

Rds(on) is usually spec'd when it is turned on very hard as a switch so its resistance is very low. It is called its triode, linear and ohmic zone. Its saturation zone Rds is determined by its Vgs and its voltage gain.
 
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