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MOSFET (Si/SiC) Forum Discussions

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I have successfully used the IRLB3813 in numerous portable power tool designs to drive PM brush motors in the 450W range. All these tools are powered by LiPo 18V nominal 20.5V max removable batteries and operate with the IRLB3813 as a PWM'd switch to ground (i.e. not a bridge). A new tool is presenting a problem with IRLB3813s failing upon battery insertion. These failures can be on the first insertion, or sometimes will not happen many hundreds of insertions or more. The difference in this tool design is that the motor leads are 42cm of 14AWG - considerably longer than the earlier design where the motor leads were 10cm or less. What appears to happen is that the IRLB3813 bursts into oscillation perhaps due to parasitics in the motor leads. The pcb layout is clean with a robust power and ground plane. For transient suppression a 4A schottky diode clamps the drain to the +battery and the battery bus is shunted by a 24V TVS diode. When the failure occurs a brief period of RF oscillation - somewhere around a millisecond - causes the IRLB3813 to permanently "short" at around 10 ohms. When operating properly, the gate drive is a crisp and clean 15V 2KHz
PWM signal and the IRLB3813 handles the 500W load staying nice and cool in the process. My working hypothesis is that the IRLB3813 maximum Vds of
30V isn't quite large enough to handle these oscillations and as a result the device breaks down. One may think that the schottky would clamp this voltage but resonance(s) in the battery may limit that clamping. I am planning to run tests with a higher voltage FET, the IRFB7437. Any feedback or suggestions would be welcome.
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1 Solution
srhim1971
Employee
10 replies posted 5 replies posted First question asked
Employee
The oscillations can be suppressed by a snubber circuit. You can use combinations of resistors and capacitors.

Additionally you can check whether or not the device works in the Safe Operating Range. See this Appnote:
in chapter 2.1

The measurement results can be compared with the simulation. Here we have an Appnote with detailled Mosfet Behaviour Analysis:

See "documents" and " Application Notes".
Inside

View solution in original post

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2 Replies
srhim1971
Employee
10 replies posted 5 replies posted First question asked
Employee
The oscillations can be suppressed by a snubber circuit. You can use combinations of resistors and capacitors.

Additionally you can check whether or not the device works in the Safe Operating Range. See this Appnote:
in chapter 2.1

The measurement results can be compared with the simulation. Here we have an Appnote with detailled Mosfet Behaviour Analysis:

See "documents" and " Application Notes".
Inside
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Blavall1
Employee
Employee
Hi Consultofactus - are you still having this problem with the IRLB3813? Or is this now resolved for you? Can you let us know?
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