Thanks,
The problem with pulse transformer gate drive is the following…..
1..You always need to drive the lower FETs through pulse transformers too, in order to get the same propagation delay, so you need more coils in the former.
2A….The source of the gate drive current is on the primary side of the pulse transformer, so that high current pulse has to traverse a potentially long bit of PCB to get to the FET gate. (with the method of post #1, there can be a gate driver right next to the FET itself, so the high pulse current can be in a tiny loop)
2B….Two gates can be driven from the same former, however, this means your gate drive has to be able to provide all that extra current to actually adequately drive those two FETs from the one driver. With the method of post #1, each FET can have its own dedicated drive chip.
3….Pulse transformer gate drives virtually always need a turn-off PNP to be included, so there’s extra parts.
4….Pulse transformers for FET gate drives need to be precision engineered, so that they have absolute minimum leakage inductance. If your winder has a bad day when winding them, then your SMPS batch may suffer too high switching losses and fail.
Its noteable how even tiny amounts of leakage inductance in a pulse transformer gate drive can really slow up the switching transient of the FET.
5….Pulse transformers for gate drives are rarely if ever available to your particular spec off-the-shelf, you virtually always have to get them custom wound.
6…Pulse transformer gate drives always need series resistance to be included in order to prevent ringing with the leakage inductance of the pulse transformer. There needs to be a resistor in both primary and secondary sides of the pulse transformer. This resistance always ends up being bigger than you would like, and means that your FET’s switching transients are always slower than you would like, meaning you get more switching losses.
7….If the method of post #1 is used, then you can use an 1EDI20N fet driver right next to the fet, and get absolute optimal turn off and turn on of the FET. (the 1EDI20N FET driver has separate pins for turn off and turn on.)
1EDI20N gate driver:
https://www.infineon.com/dgdl/Infineo...4790299add6112
.....after all this, I am amazed that nobody is using the method of post #1 with SMPS.
Attached simulation shows a ltspice sim of Pulse transformer solution