Deadband for PWM style driver?

[ACharnley]

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]

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]

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]

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.

 

[ACharnley]

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!

 

[dknguyen]

Two gates to Q6 and Q9, just


Problem there is it defaults to ON with a NFET. Not good for active rectification!

That's what pull resistors are for

 

[ACharnley]

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.