Ripple current is the current that flows through output inductor at switching frequency. It causes losses in inductor's wires, mosfets' Rdson and capacitors' ESR.
My battery voltage will be near 60V and if the load is assumed inductive so I preferred Vds>=100V mosfets. I found IRF6645 is the best among VDS>=100V FETs. Am I wrong?
I suspected the small sign of turning on again at the lower gates. I'm trying to lower it.
I got the lower gate voltages when the load is resistive or inductive.
when it is loaded resistively small voltage spikes seen on both gate voltage.
but when it is loaded inductively the spikes too high!
Is that normal the gate voltage having high spikes with inductive load?
A little spike is expected but this much more than expected. Also as you can see the behavior is not the same although at the same edges of the signals!?
Attachments
Hmmm... Why is it usual? What is the reason for that turning on again?
Thank You in advance.
Last edited:
Cgd injects charge to gate while Vds is increasing. The opposite impulse also can be seen at negative Vds edge, when it is not caused by the FET itself.
Thank You.
Looks like it is an "unavoidable" effect?
And what is the reason this time?
Thanks.
Last edited:
A small capacitor (~330pF) directly at gate to source terminals can tell if that's really miller Cgd problem.
This capacitor slows down di/dt phase but leaves dv/dt basically same fast, and paracitic capacitance divider Cgd/Cgs will hopefully divide enough now to stay below Vgs threshold.
Try it now just for fault tracing
This capacitor slows down di/dt phase but leaves dv/dt basically same fast, and paracitic capacitance divider Cgd/Cgs will hopefully divide enough now to stay below Vgs threshold.
Try it now just for fault tracing
- Status
- Not open for further replies.