measure the rdson during final test

[sj95]

Dear all:

How to measure the rdson during final test accurately ? if the rdson is 5m ohm, the contact resistance between equipments is significant.

Any method to get a certain measure result ?

tks

 

[goldsmith]

Hi
It is simple ! put 15 volts across the GS junction of your mosfet and then give 10 volts as VDD , then use an ammeter and , measure , it's current , thus you can find Rdson . another way is putting a pretty low value resistor as RD and measuring VDS instead of Id , and easily Rdson will given .
Best Wishes
Goldsmith

 

[KonstanU]

Do not invent new way of measurement. Exist standard method. Look at the MIL-STD-750E standard.

 

[godfreyl]

It is simple ! put 15 volts across the GS junction of your mosfet and then give 10 volts as VDD , then use an ammeter and , measure , it's current....

So if the rdson is 5m ohm, you expect the meter to read 2000 Amps? :roll:

That is not a good way to measure rdson. It is a good way to destroy the MOSFET and maybe start a fire.

 

[goldsmith]

Hi Godfreyl !

So if the rdson is 5m ohm, you expect the meter to read 2000 Amps?

Who told that ! i told that as an example ! voltage can be lower ! and of course via a resistor ! i have tested this was more than some hundreds ! perhaps you want that i show you ? if yes , no problem i can !


Hi Konstanu

Do not invent new way of measurement. Exist standard method. Look at the MIL-STD-750E standard.

I didn't learn to be a user ! i learned to be an inventor and a designer ! not just copy and paste !


Best Wishes
Goldsmith

 

[godfreyl]

Who told that !

You did.

i told that as an example !

Exactly. You told that.

It is a bad example. You said to put 10V across the MOSFET and measure the current with an ammeter. 10V/5mΩ = 2000A. Trying to measure like that is a bad idea.

i have tested this was more than some hundreds !

I don't believe you tested that way even once. If you had, you would know it is a bad idea.

voltage can be lower ! and of course via a resistor !

You did not say to use a resistor, but if you do connect it via a resistor, then your ammeter reading is worthless.

Your second suggestion, to use a resistor and a voltmeter is good.
:grin:

 

[goldsmith]

Hi Godfreyl

another way is putting a pretty low value resistor as RD and measuring VDS instead of Id , and easily Rdson will given .

You did not say to use a resistor

I told that at first ! i think you didn't read it carefully .
By the way i don't think that you can have access to a power source with ability of 2000 Amperes ! ( however i have a 0-60 V 0-200A in my laboratory ! but it is impossible that i test my mosfets with that ! )
If you use a limited power supply , you will have a limited current ( e.g 2 A or 5 A ) then with a precise voltmeter you can easily find Rdson too . however you can decrease VDD lower than that .

You said to put 10V across

That is an example , i don't think any body put that voltage ! just an example ! :-D

I don't believe you tested that way even once. If you had, you would know it is a bad idea.

Why you can't believe ? how ever it is not important ! because i didn't many measurements with this way ! but some tricks are required ! it is up to each designer ! for example for some circuits i have some ways that i know you can't believe them . but i have used them in my designs ! ( Recall : i learned to be a designer and inventor instead of a simple user ! time teaches me this ! )
Best Regards and Best Wishes to you ! :wink:
Goldsmith