Hi, We are using LT8311 as sync rectifier controller of forwward converter.When FG pin connected to forward FET, there is no issues.But when CG pin connected to chatch FET, input current is increased and efficiency is goes down.Is this light operation?
Wave forms are,Upper : VDS of primary main switchMiddle : FGLower : CG
If this happens at heavy load, then something is wrong.
At light load or no load, it is normal. After the CG pin is connected to the catch FET, the converter operates in forced continuous conduction mode which is less efficient than DCM. If the DCM operation is acceptable, then the LT8311 can be programmed to achieve that.
A couple of week we asked operation of the LT8311. tried to several ways to solve but still there are problems...
Well Big Spike noise has been occured on output pulse which is Vgs of the Catch FET side as attached. However Forward FET is not so bad.
it looks aprox twice of level against exepted pulse voltage. Are there any ways to supress this spike noise?
it looks aprox twice of level against exepted pulse voltage. Are there any ways to supress this spike noise?PDF
Looks like you've already added some snubber there.
The spike is related to the secondary leakage inductance and the parasitic components of the catch MOSFET.
Try to add some RCD clamp and/or use a higher voltage rating mosfet.
We have done suppressed catch FETs spike, but appraed similar level spike noise to side of forward FET.
Is this reasonable phenomina? We believe that Spike of Catch side is larger than Forward side.
Could you please tell me possibility, or inidicate please if unbelievable.