Ciss is the capacitance Cgs + Cgd, and I want to test it by my LCR meter.
So how can I do it? should I short-circuit D and S ? if i do this, obviusly I am short-circuiting the 15V power supply dc bias.
V_gs = 0V.....and as FvM correctly stated this is the DC operation point.
--> use a high ohmic resistor across G and S to ensure 0V DC.
But you want to test input capacitance:
--> connect a high quality foil capacitor from your ESR measurement device to G of the mosfet.
The capacitance need to be way higher than the exoected DUT capacitance to avoid influence in the measurement result.
If you take a 100 times higher capacitor...you should be safe.
Note: the AC voltage should be small enough to be below V_gs_th.
V_gs = 0V.....and as FvM correctly stated this is the DC operation point.
--> use a high ohmic resistor across G and S to ensure 0V DC.
But you want to test input capacitance:
--> connect a high quality foil capacitor from your ESR measurement device to G of the mosfet.
The capacitance need to be way higher than the exoected DUT capacitance to avoid influence in the measurement result.
If you take a 100 times higher capacitor...you should be safe.
Note: the AC voltage should be small enough to be below V_gs_th.
so when I test Ciss , i short the D and S and the real test condition is : VGS = 0 V, f = 1 MHz,
and when I test Coss, I short the G and S and the real test condition is : VDS = 25V, f = 1 MHz,
After I contact with the support of a manufacturer. what i know is:
When test Ciss, LCR meter is across the G and S, Vds = 15V, and there is a big cap between the D and S to AC-short the D and S.
When test Coss, LCR meter is across the D and S, Vds = 15V, and G and S is really shorted.