Hey Guys,

I have been working on my first PCB which is used to drive BLDC motors. Basically it is a 3 phase inverter. I am using the IR2103 as the mosfet drivers. The mosfets are F3205s. After fabrication, for some reason I am experiencing some level of shoot-through in half bridges. When no load is connected, the mosfets just get hot. They do still provide current through the phase outputs, but im guessing at low efficiency. I've been try to analyze if im using the components wrong but am not able to find a solution. Is there something obvious I am not doing as per my schematic below? Any leads would be greatly appreciated!

1,2,3 are pwm input for each phase. A,B,C are the current outputs for the motor phases. I have not used copper pour on any layers. Is that an issue?


Thank you,
Khan

 

Your Gate-Resistors are probably too high of a value.

This would be easier to determine if You would provide
the complete part-number for the FETs,
or better yet,
provide us with the PDF,
so we don't have to look it up and then hope it's the correct part-number.

There are a lot of factors that go into selecting a Gate-Resistor,
the most important of which are the
Switching-Speed that You require, and the FET Gate-Capacitance.

You could also be getting noise on the Inputs to the Gate-Drivers.
If the Inputs are EVER in a "Floating" condition they will probably oscillate.
This possible Oscillation-Frequency may be too high for You to detect.
.
.
.

 

This would be easier to determine if You would provide
the complete part-number for the FETs,

They are right there in the schematic. Would it have been eaasier for you to read them if he had used red instead of blue in the schematic?

 

What LowQCab said is very true. 100Ohm might be high for a gate resistor.

Look at the datasheet for the FET and you will see the turn on/off delay and rise time was tested with Rg =4.5 Ohm. Higher resistance will slow down turning on/off time, increase rise/fall time which will increase resistance, AND keep them on for longer which may cause it to be on when another phase turns on.

Do you know what your PWM programmed dead time between phases is?

Also, I noticed you don't have several bulk capacitors at the input of your 48V. Can you say why you dint use those?
It will increase voltage rail stability and reduce voltage transients.

Lastly, yes a good-thickness copper pour can help dissipate heat. You can always get some sticky heatsinks and get some airflow to cool the parts.

Nick

 

Also, I suggest you place inverse parallel diodes with the gate resistors (whose value I suggest you change to something between 10 and 20 ohms) so as to minimize gate discharge time when the fets are switched off.