Issue in driving senored BLDC motor

Hello All,

Good Morning!!!

I have developed 12V and 24V BLDC motor driver with max current upto 20A

The driver is working fine. The efficiency is good.

Sometimes it is giving the issue. Sometimes once I turned on the power then suddenly blast happens and current reaches 70-80A.

Please suggest me remedy over this issue. My design is still not getting approved just because of this issue.

Please let me know if you will need more information on it.

I'm really not a motor control specialist - but, it's very logical for the startup current to be high.
At T=0 the motor is at rest and its coils act as a short circuit ( short circuit current = V / coil resistance ).
The current will drop as the motor will start to spin.

What (I think) can be done to mitigate the effect:
1. Ramp up the voltage slowly during startup.
2. Close the BLDC control loop as fast as possible.

Hello Shaiko,

Yes, You are right. Let me tell you what is happening.

The issue is coming once you turn on the power natch on.

Suppose, I am turning power natch ON for first time. motor is working.Natch turned Off. Motor stopps.

When I am turning power natch ON for second time.Motor is working. Natch turns off. Motor stopps.

After 11th time same operation, motor working fine.
At 12th operation, once natch turns on, quickly there is a spark and current in power supply reaches 80-100A. Motor not even rotate. At the moment, you turn on the natch, there is a spark. The conclusion is both MOSFET'S of one phase burned and the current sense resistor burns.

This happens at random stages. Sometimes at 2nd time. sometimes 9th time. Some times 20th. sometimes 7th. Sometimes 1st time.

1. Ramp up the voltage slowly during startup.
2. Close the BLDC control loop as fast as possible.

Click to expand...

I have done this. The motor is slowly starting.

Please suggest.

Are the MOSFETs protected by flyback diodes ?

Are the MOSFETs protected by flyback diodes ?

Click to expand...

According to previous post, the circuit topology is three-phase bridge (two transistors per phase). No need for "flyback" diodes.

Without circuit and control algorithm details, it's impossible to analyze possible failure causes, I think.

Internally they have diode.

How to do it externally.

- - - Updated - - -

Hello FvM,

Here is my circuit diagram.

Please let me know the root cause. The issue is coming randomly somtimes when power knob is tuned on. Once it starts, if I keep running for several hours with full load, then also there is no issue. The issue is coming only at start.

View attachment AP3.pdf

The schematic isn't very informative without any component type and value.

As far as I see, there's high risk of causing shoot-through during power-on. It's also not obvious that the high side driver circuit is providing proper gate voltage levels to turn the FETs fully on.

How are you controlling motor current? In case you're implementing PWM control, did you check that the gate signals are fast enough to keep switching losses within acceptable bounds?

Hello FvM,

I always like your quick response. Thank You very much.

I am controlling motor current by PWM technique. I have checked the gate signals in DSO.

The control is fine. The issue is coming randomly at power on only.

If motor is running properly after power ON and after keeping motor turn on for several hours with full load/without full load. There is no issue. Randomly power on issue is coming.

Hello Guys ,

The issue is not resolved.

Please help me to understand why at random turn on, the blast happens.