MOSFET Temperature measurements

[MadBunny]

Hello all,

I am working on project BLDC motor application. Here,I have to measure the temperature behaviours on MOSFET's in bridge driver in BLDC motor control for trapezoidal commutation. I have temperature sensors to measure the MOSFET's and have a software to see the temperature values for all MOSFET's. Can you please tell me How will be the characteristic curve between?


Thanks in advance

 

[Harald Kapp]

How will be the characteristic curve between?

Please be a bit more specific. Your question is a bit short on detail.
Between what? And which characteristic do you refer to (independent parameter, dependent parameter)?

 

[MadBunny]

Please be a bit more specific. Your question is a bit short on detail.
Between what? And which characteristic do you refer to (independent parameter, dependent parameter)?

I would like to see If Mosfet's can sustain if the motor keeps running for more time and how will be the temperature variations on Mosfet's. So for that, Do I have to take characteristic between temp and time or what?

 

[Alec_t]

Yes, you can chart MOSFET temperature and time. You also need to monitor the motor somehow to ascertain if it is running or not.

 

[Harald Kapp]

Charting the temperature vs. time makes sense for the startup operation only as the temperature should stabilize at a certain operating point after a short warm-up time.
What may be much more important is imho temperature vs. motor load. Motor power will vary with load and thus the power dissipation of the MOSFETs will, too.

Note that you are monitoring cas etemperature. You'll have to do some math using the thermal resistance Rth(case-junction) to find the temperature of the semiconductor which is the real critical parameter (typically max. 150 °C are allowed, the datasheet of the transistor has the specs).

Btw.: is this 'application' some kind of task assignment, homework, school project or similar?

 

[MadBunny]

Btw.: is this 'application' some kind of task assignment, homework, school project or similar?

Thank you for the reply, It's a school project.

 

[MadBunny]

Yes, you can chart MOSFET temperature and time. You also need to monitor the motor somehow to ascertain if it is running or not.

Do you mean all the Mosfet's temperature on bridge driver vs time?

 

[Harald Kapp]

If you use different types (NMOS, PMOS) monitor at least one of each type. If all MOSFETS are of the same type, it may suffice to monitor a single tranbsistor.

 

[MadBunny]

If you use different types (NMOS, PMOS) monitor at least one of each type. If all MOSFETS are of the same type, it may suffice to monitor a single tranbsistor.

I am using all Mosfet's N-channel enhanced. So it is alright if I monitor one MOSFET temperature right?

 

[Harald Kapp]

Should be o.k.
If you have free temp. measurement channels, measure as many MOSFETs as possible. This will give you a better statistical result and will also hint at possible asymmetries between high side and low side.