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Deadband for PWM style driver?

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ACharnley

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11.png

Hi, produced the circuit above for driving an N-fet highside (VOM opto's are currently hard to come across). Am I correct in saying Q5 and Q9 could potentially short fetDC so I should look to include a deadband via a MCU?
 

dknguyen

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It's possible, but you won't be able to implement deadband with that circuit since Q5 and Q9 are being driven by a common signal.
 

dknguyen

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But if that is just being used to drive a FET you can swap the transistors so the NPN is on top and the PNP is on the bottom. Then you won't need to worry shoot-through since they will use each other as negative feedback so both be fully on at the same time.
 

ronsimpson

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There must be 100 Gate Drivers for MOSFETs like this. This one will allow the top and bottom transistors to be on at the same time but some have a function to stop two transistors on. Some have a delay for turn-on/ turn-off. Many options. This one is good for 600 volts.
2018-09-19-163112_1184x624_scrot.png
 

ACharnley

Member
Two gates to Q6 and Q9, just
But if that is just being used to drive a FET you can swap the transistors so the NPN is on top and the PNP is on the bottom. Then you won't need to worry shoot-through since they will use each other as negative feedback so both be fully on at the same time.
Problem there is it defaults to ON with a NFET. Not good for active rectification!
 

ACharnley

Member
There must be 100 Gate Drivers for MOSFETs like this. This one will allow the top and bottom transistors to be on at the same time but some have a function to stop two transistors on. Some have a delay for turn-on/ turn-off. Many options. This one is good for 600 volts.
View attachment 114604
This looks like a good alternative to the VOM isolated driver. Unlike the VOM however it's bootstrapping the high side drive which requires a constant PWM signal to sustain it. Not so useful in a relay style application.
 
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