I designed a Half-Bridge power supply using Gate Driver Transformers to drive my two MOSFETs. It's working great, I winded the two transformers around very small toroids with some turns, I didn't calculated anything, they just worked!
Now, I'm trying to understand how to select a proper gate driver transformer. My switching frequency is 100kHz so I'm aiming for a rising/falling times of about 300-400ns or even lower. I went to
DigiKey and found this 1:1 ratio transformer. It claims a primary inductance of
On this page I found this picture:
According to this my inductance should be between 0.5 and 2mH so 10mH is too much. I tried to do some calculations using
di = v dt / L. I'm powering my driver transformer using a 6A peak MOSFET driver (MCP1407) with a 12V output, at 100kHz and with 50% duty cycle:
di = 12V * (5*10^-6 / 10*10^-3) = 6mA!!!
Only 6mA? I'm pretty sure I'm really missing something big, this drivers have high peak currents to rapidly charge/discharge the gate capacitance of the MOSFET.
So my questions are:
- Isn't 10mH a really big inductance for a fast transition?
- According to the picture, the inductance for 100kHz should be between 500uH and 2mH, why can't it be lower (or higher)?
- How do you exactly select a gate driver transformer and how can you calculate how fast the current/voltage will rise on the MOSFET's gate to ensure proper rise/fall times?