I am using a driver Si830 to drive a half Mosfet bridge, and for the voltage 12VP I am using a flyback (LT8047)

enter image description here I want to know how much current is drown from this sure to be source the flyback can provide it, knowing that the max gate drive current is 0.5A and the voltage at the high side is 400V.

Thank you


The peak current can be quite easily calculated - 12V/4.7ohm = 2.55A. But this does not tell you much. It happens only the first time and C401 should handle this, not the PSU.

The average current is proportional to your switching frequency (f) and your MOSFET's gate charge (Q) (from MOSFET's datasheet).

The most simple calculation is:

I = Q . f

This does not include losses in gate resistor, driver, etc. I would double the result when selecting gate driver supply to be sure.

  • \$\begingroup\$ thank you very much, an other question please, how can I select the resistors of the gate RG1 and RG2 like this picture i.imgur.com/5Zmwd1N.png \$\endgroup\$ – Dark Mythos Jun 13 '17 at 17:45
  • \$\begingroup\$ @DarkMythos One way is to calculate them for driver's maximum source/sink currents to have faster switching times and to reduce switching losses. However faster switching times produce more EMI/EMC and require larger and more expensive input filters. \$\endgroup\$ – Todor Simeonov Jun 13 '17 at 18:32

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