MOSFET problem open even two MOS are not open

[yassin.kraouch]

i use this MOSFET https://www.fairchildsemi.com/ds/FD/FDS9934C.pdf

the schematic is

the gate of the PMOS is connected to Vcc and the gate of the NMOS is connected to GND, the problem that i found there is a current that pass throught R1, have you an idea about this problem ?

 

[keith1200rs]

You have drawn one as PMOS and the other as NMOS but they both have the same part number.

Keith.

 

[srizbf]

interchange the source and drain of Q2-pmos.

 

[alexan_e]

Is your question related to the leakage current of the mosfets?
A mosfet can't turn completely off , there is a current of a few uA passing through the mosfet even when it is off, the parameter is described in the datasheet.

Alex

 

[keith1200rs]

Is it a simulation problem or have you actually built the circuit?

Keith.

 

[alexan_e]

You have drawn one as PMOS and the other as NMOS but they both have the same part number.

Keith.

I have just opened the datasheet and FDS9934C is a complementary dual mosfet, one P-mosfet and one N-mosfet

Alex

 

[ALERTLINKS]

The circuit should be assembled to test leakage like this.

 

[keith1200rs]

If it is a simulation then they are called FDS9934CQ2 for the PMOS and FDS9934CQ1 for the NMOS. Also, it is a thermal model with the fourth terminal being for temperature rather than the BULK. It is important to know whether it is a simulation problem or construction problem (in which case the incorrect connections could be a possibility).

Keith.

 

[yassin.kraouch]

no it is a practical result, i test the circuit practically,
this is not a a leakage current Alex, i measured the current, it is about 2mA!!

 

[alexan_e]

How were the mosfets connected, like shown in post #1 or like shown in post #7 by ALERLINKS ?

 

[Raza]

Hi,
Here is the package internal diagram of the device.

Define here with pin numbers for your diagram. You did not mention whether it is assembled on PCB or simulated and what is the current you measured?.

 

[keith1200rs]

My guess is you have them connected the wrong way round (PMOS where the NMOS should be and vice versa). And double check that you have the source & drain the correct way round one each.

Keith.

 

[yassin.kraouch]

My guess is you have them connected the wrong way round (PMOS where the NMOS should be and vice versa). And double check that you have the source & drain the correct way round one each.

Keith.

i also cheked this, the connection is right

---------- Post added at 18:08 ---------- Previous post was at 18:03 ----------

how were the mosfets connected, like shown in post #1 or like shown in post #7 by alerlinks ?

there are the same

 

[keith1200rs]

You need to check again. 2mA isn't leakage when you have 350 ohms between the transistors - they are both either turned on or you have internal diodes conducting and the remaining voltage is going through the 350 ohms. As Raza said - "Define here with pin numbers for your diagram"

Keith.

---------- Post added at 18:14 ---------- Previous post was at 18:11 ----------

there are the same

NO they aren't!

Keith.

 

[yassin.kraouch]

this is the shematic i realised in practice

 

[FvM]

That's in fact the circuit from post #7 and correct. According to the datasheet, the leakage current is < 1 uA. So something is wrong with your measurement method or the device.

 

[yassin.kraouch]

first i tested each circuit alone they work perfectly, but when i test the two circuit together i found this problem, i don't know why, but i test with two method and i found the same result

 

[ALERTLINKS]

There will be around 5ma in the resistor if battery is connected in reverse. Check it out if this not the case.

 

[yassin.kraouch]

i have a question what is the maximum value of Vgsth ?

 

[alexan_e]

It is shown in the datasheet,
for the N-mosfet Q1 min= 0.6v typ= 1v max= 1.5v
for the P-mosfet Q2 min= -0.6v typ=-0.9v max= -1.2v

alex