INN4377 unexpected switch frequency, SOA protection, audible noise
Posted by: Nick_Weaver
on
I have design based on der-960 with INN4377.
In load below ~4A(20v) power supply work stable without any noise. But after some threshold when I try rich 5A(20v) it jump to higher frequency instantly and I can see SOA protection(I assume it) on main switching. It's create a lot of audible noise from FB transformer.
I am not sure what can be source of issue. In theory increasing of freq should reduce a main switch current don't trigger SOA. I didn't find information about freq equation for innoswitch 4 , so could you help clarified with it?
Files
General FlyBack schematic
(154.13 KB)
20V 3A main switch drain wave form
(72.65 KB)
20V 5A main switch drain wave form
(67.75 KB)
Hi Nick,
Good day. Thank you for using Power Integrations solutions.
After reviewing the switching waveforms you shared, we didn’t observe any unusual operation on Drain voltage waveform on loads 3 and 5 A.
To help us further investigate the audible noise, could you please share the transformer construction of your current system?
As for the operating frequency of the InnoSwitch4-Pro, it follows the fundamental concepts of a flyback system and can be set between 50 kHz and 130 kHz. And information for the SOA is presented under Typical Performance Curves figure 37. of the device datasheet.
We look forward to your response.