2N7002 Idss

[Harry Dellamano]

How do I determine the Idss current at elevated temperatures and different
Vds voltages for a 2N7002? The data is given as 1.0uA at 25C and Vds=45V.
We know leakage current doubles every 10C so at +125C, Idss =
1uA*2^((125-25)/10)= 1mA but how does Vds effect this leakage current? Will
a SPICE model yield good results in this area?

thanks,
Harry

 

[Robert Baer]

Harry Dellamano wrote:

How do I determine the Idss current at elevated temperatures and different
Vds voltages for a 2N7002? The data is given as 1.0uA at 25C and Vds=45V.
We know leakage current doubles every 10C so at +125C, Idss =
1uA*2^((125-25)/10)= 1mA but how does Vds effect this leakage current? Will
a SPICE model yield good results in this area?

thanks,
Harry


Vgs VS log(Id) is a straight line; the slope depends on manufacturer

and FET type (logic, power, etc).
If one does not fix the SPICe model, it fails to follow that log
relationship at low currents.
The same could be said concerning temperature effects
Look in this NG under subject "oscillation in high-voltage" for one
of the fixes.
The other fix is to remove a (usually) 1meg resistor between the
source and drain in the model.
I have not checked these fixes over temperature.

 

[Winfield Hill]

Harry Dellamano wrote...

How do I determine the Idss current at elevated temperatures and
different Vds voltages for a 2N7002? The data is given as 1.0uA
at 25C and Vds=45V. We know leakage current doubles every 10C so
at +125C, Idss => 1uA*2^((125-25)/10) = 1mA

Close, perhaps... Vishay, for example, gives Idss leakage current
as 1uA maximum at 60V 25C, and 500uA at 125C.

but how does Vds effect this leakage current?

I can give you a few general pointers. First, for most MOSFETs I've
measured, the leakage current is proportional to Vds, which means it
can be modeled as a resistance. Assume a resistance that drops with
temperature. Ahem, until one approaches breakdown, of course.

To complicate matters, the maximum leakage current for a given type
varies considerably from manufacturer to manufacturer, and from batch
to batch. However, the datasheet maximum leakage specs are usually
VERY conservative from real parts, by factors of 100 to 10000, etc.
This also varies from manufacturer to manufacturer and batch to batch.

Will a SPICE model yield good results in this area?

For most FETs, it's doubtful.


--
Thanks,
- Win