Hello,
I have been working on a line follower robot as a part of my university project for quite some time now. We recently upgraded the motor to a much more powerful one, which made it horribly noisy. This was due to the low driving frequency, around 2KHz, which wasn't a problem with the previous setup. I tested the circuit at 20KHz and the MOSFETS started heating up really badly really quickly and I can't quite figure out why.
I am only switching the bottom transistors of the H-Bridge since the top ones have a very slow driving circuit and heat up immensely if switched faster than a few hundred times per second. The bottom (N channel) transistors were driven from a signal generator with an output impedance of 50ohm, 12V pp voltage.
Now, I can only see two reasons for the transistors to heat up so much:
a.) Avalanche breakdown occurs on each switch on/off cycle. This is very unlikely, as there are schottky diodes in place to prevent it. The circuit even worked with regular diodes in place, so this can pretty much be scratched out
b.) Large switching losses due to poor gate driver. Maybe the gate isn't being driven hard enough by the signal generator. I was thinking of augmenting the gate driver in some way.
For the gate driver, I was considering a totem pole with pnp/npn transistors, or something like a NOT gate made of logic level MOSFETs. However, I don't know whether shoot through wouldn't be a problem with them.
What should I check next time I am in the lab?
I have been working on a line follower robot as a part of my university project for quite some time now. We recently upgraded the motor to a much more powerful one, which made it horribly noisy. This was due to the low driving frequency, around 2KHz, which wasn't a problem with the previous setup. I tested the circuit at 20KHz and the MOSFETS started heating up really badly really quickly and I can't quite figure out why.
I am only switching the bottom transistors of the H-Bridge since the top ones have a very slow driving circuit and heat up immensely if switched faster than a few hundred times per second. The bottom (N channel) transistors were driven from a signal generator with an output impedance of 50ohm, 12V pp voltage.
Now, I can only see two reasons for the transistors to heat up so much:
a.) Avalanche breakdown occurs on each switch on/off cycle. This is very unlikely, as there are schottky diodes in place to prevent it. The circuit even worked with regular diodes in place, so this can pretty much be scratched out
b.) Large switching losses due to poor gate driver. Maybe the gate isn't being driven hard enough by the signal generator. I was thinking of augmenting the gate driver in some way.
For the gate driver, I was considering a totem pole with pnp/npn transistors, or something like a NOT gate made of logic level MOSFETs. However, I don't know whether shoot through wouldn't be a problem with them.
What should I check next time I am in the lab?
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