test mosfet specification

[Amro eid]

hello colleagues
test mosfet specification
there is big problem becam famous now many bad new mosfet in the market
for example IRFP460A it.s Characteristics is Drain to Source Voltage
is 500v and Drain Current is 20A BUT WHEN I BOUGHT 4 transistors in akai plasma
burned SO FAST AND DAMAGE DRIVER IC.S AND POWER SUPPLY UNIT
AFTER REBUILD GET OLD 4 TR IRFP460A
TV WORKS GOOD many colleagues KNOW THAT (especially TR POWER AND MOSFET)
have not the same specification which in data sheet( original not exist in most cases )
so i Need any tools to measure drain current and Drain to Source Voltage....etc
to make sure it is good before i put it in the set
test circuit which exist in some data sheet not useful
any body have idea document or tools for seal to do this to avoid big damage please help with any info
kind/regards

 

[ServoAmp]

problem:
I may need a little clarification on this problem. I do not understand the term TR Power.
It seems that you bought some bad parts in that they failed immediately when installed in a plasma display you are working on.
You would like to verify component parameters by test before installing to avoid damage to the unit when the component fails.
I have heard of counterfeit parts on the market. I know of one company that is taking pictures of the die for incoming inspection by quality control.
The die size of the counterfeit parts is obviously smaller that the real parts. The top of the package is sanded off exposing the die for inspection under a microscope. Only 1 or 2 parts have to be tested in this way per lot.
This inspection process may be the most cost effective solution.
As for testing:
I think that you need to verify the power handling capacity of the part, Including thermal resistance from junction to case (verify internal bonding and structure) as well as case to heat sink ( package integrity)
Other MOSFET parameters that affect power handling capacity are Vds, Ron, gate charge, switching speed.
Testing all of these could be expensive, but as in the above inspection you may get by with testing 1 or 2 per lot.
Calculate Switching loss
Switching loss can be hard to calculate because it is a function of many variables, such as MOSFET parameters, methods of driving switching devices, snubbers,, etc.
Unless all of these factors are considered the calculation is at best a rough approximation.
For this reason I recommend the following:
Measure switching + conduction loss
The easiest way around this is to measure the temperature rise of a known good device in an actual working model.
A DC current would then be injected through the device and adjusted to give the same temperature rise on the same heat sink configuration.
The power dissipation (switching +conduction loss) can then easily be calculated by DC current * DC voltage.
You would perform the above test using a know good device in a know good system.
Once you have the DC voltage and Current and temperature rise data for a specific heat sink configuration, You can use this configuration to test new parts.
Your device tester would be a simple test circuit to supply this same DC current and voltage to the device under test mounted to the specific heat sink configuration.
This test could easily verify Vds and on resistance. Measure Gate charge with a capacitance meter and all that is left is switching speed.
Some things to be careful about:
This actual working model must contain the actual drive circuitry and heat sink as well as any other associated circuits like snubber etc.
It is very important to use the device just as it is in the system with the exact same heat sink configuration.
Even changing from thermal compound to an insulating thermal pad can alter the thermal resistance enough to invalidate your results.
Not having the correct Torque on the heat sink mounting screw can alter your results.
If you use a different heat sink or different airflow it will invalidate the results.
For example enclosed in a chassis versus external to the chassis. (invalid)
The Heat sink must have the same thermal resistance, size, mass and airflow as the actual system for this to be valid.
Tester:
The power dissipation (switching +conductin loss) is then DC current * DC voltage.
You would perform the above test using a know good device in a know good system.
Once you had the DC voltage and Current and temperature rise data for a specific heatsink configuration,
Your device tester would be a simple test circuit to supply this same DC current and voltage to the device under test mounted to the specific heat sink configuration.
Pretty simple:

 

[Amro eid]

hello
thanks for reply
term TR Power means switching transistor in power unit which connected to chopper in primary side which works with 295v
i need to make test circut to measure the real drain current
but with your way i need evey time to get working circuit work with the same mosfet to make comparison
this is not what i need
i need to build test circuit similar to the one in datasheet and change the supply voltage and load and frequency
if any body have info about that please help
kind/regards

 

[Amro eid]

hello again
i think the topic i wrote not clear enough to make every body understand
so i'll explain more hope somebody have any solution
i need test circuit for the real Power MOSFET Specifications
i faced problem about IRFP460A
workes in plasma akai PDP-46TS1 in x board
4 tr mosfet was defect also it is normal in this case driver ic.s
became defect
and smd resistance
i rebuild circuit put the tv in ac voltage and feed the x board with 170v through
lamp 200 wat i get very bad result all electronic components
all burned
i was so depressed
buta friend of mine told me he have
scrap tv lg plasma have this IRFP460A
i rebuild the circut again
tv works good
then problem was in bad kind of IRFP460A
so that
i need any tools chek (drain) current is 20 amper as in datasheet
and vdss Drain to Source Voltag 500v as as in datasheet
if i lost one transistor during test the mosfet it is better than i lost all
componnents (and time and mony)
if any body have circut to do that
or any hint please write to me
regards