push pull switching transistors , DT/DV

[danny davis]

I'm confused on DT/DV on push pull switching transistors or IGBT, mostly the values of the resistors are the same value to keep the DT/DV in sync with the on time and off times, but if the resistor values are slightly different between the push pull switching transistor pairs , what happens?

When transistor switches or IGBT that are used as a Push pull network , if the push or pull is displaced or offset what happens?

Because the PUSHing transistor switch will turn OFF , but the PULL transistor switch will still be on if they are not synced up, what will this do?

When using Two IGBT transistors as a push pull network, you have to use the same value Resistor GATE value

We use 24 ohms as the Resistor GATE value for both IGBT transistors , they are configure for a push pull network

If one of the Resistor GATE which is called RG , is lets say 22ohms or 20ohms or 15ohms on either the Push or pull switching Transistor or IGBT transistor it will cause a displacement and offset of timing, what will happen?

example pushing switching transistor or IGBT RG is 24ohms
pull switching transistor Or IGBT , RG value is 20 ohms

What will happen?

My manager said that one of the IGBT will have a different DT/VT , But if both pull pull IGBT have different DT/VT what does that mean?

The push IGBT will shut while the pull IGBT will shut off later , causing a short?

 

[FvM]

Transistor switches in push-pull configuration have to be operated "break before make", this is usually achieved by generating non-overlapped gate control signals. The delay between both gate signals is also named "dead-time".

Selection of gate resistors is a different thing and not primarly related to delay between push-pull switch activation, although the dead-time might need adjustment according to the actual gate resistor values. Gate resistor dimensioning is mainly a trade-off between low switching losses at one and low EMI on the other side.

 

[danny davis]

What sets the dead time?
what do u mean by break before make?

 

[FvM]

what do u mean by break before make?

I mean what engineers mean when they use the term. It's common terminology for mechanical switches and rather self-explanatory, I think. https://en.wikipedia.org/wiki/Break_before_make#Contact_terminology
The wikipedia article explains the term as "interrupt one circuit before closing the other"
.
Dead time is generated intentionally in the control circuit, e.g. a pwm controller. It's chosen by the designer according to the requirements of the used switch transistors. You might chose several 10 ns for MOSFETs up to 1 or 2 µs for high power IGBTs. Some gate drivers are able to generate deadtime internally by asymmetrical delay of driver signals. It's also possible to generate it by RCD circuits