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The PWM signal through gate drive transformer drives power transistors only, power transistors & 2 X 470uF capacitor form half bridge converter (please read on half bridge converter) which in turn drives the main transformer.
The left side transformer is called as proportional base drive transformer, this transformer creates the floating base drive current proportional to the load for half bridge transistors. Right side transformer is the main power transformer.
Are you sure that you are failing common mode EMC test & not differential mode EMC?
If you are sure that you are failing due to common mode noise, Y caps will help. Please note adding Y caps will also increase your chassis leakage current
& make sure you are meeting specifications for leakage...
uninsulated conductor voltage spacing
For working voltage isolation (non safety)
voltage peak or DC between 30V<=V<100V spacing should be 0.1 + Vpeak X 0.01
between V=>100V spacing should be 0.6 + Vpeak X 0.005
Flyback converter sometimes need post LC filter to reduce output voltage ripple derived by tighter specifications,
If you add this extra LC filter & close your feedback loop after the LC filter, stabilizing the feedback loop poses additional challenges, fast loop & slow loop concept will always...
I was referring to the TI Appnote SLU172 & zener as shown at the location below
Diode D4 is positioned at the output of the controller, possibility is they are trying to limit negative going swing on UC3854 drive pin to prevent damage to the controller IC.
if they use zener they should...
The Zener diode in this application prevents saturation of the error amplifier which helps / prevents current overshoots during zero crossing or power line dropout condition
Try winding few turns (5~6 or more ) of your PC communication cable (USB may be)on an common mode choke toroid core (preferably high perm ), this will reduce common mode current spikes generated from power switching to get coupled to common mode path causing communication loss.
If you lay your CT tracks one over other (no other switching track should overlap or cross these tracks) you can use one burden resistor near controller & feed slop comp ramp into it.
If you split your CT burden resistor (increase value by 2 & then parallel them at 2 different locations) & put one close to CT & the other one close to controller will give you better noise immunity, also there should be separate return track just below the positive CS track in the layout to...
you will need at least 3uF to filter noise & meet differential EMI at the same time.
you can calculate capacitor based on your inductor pk-pk ripple current & required EMI specs to meet.
(also make sure the film capacitor can handle the RMS ripple current.)
1649801379
Is this a CCM...
If you have low side current sense resistor then the pre-filter capacitor should be connected to bridge rectifier negative (not on the source of the MOSFET) (i.e. between Bridge rectifier positive - closer to inductor & bridge rectifier negative)
Do not see pre filter capacitor after bridge rectifier in your schematic, please add a film capacitor after bridge rectifier to support & filter the high frequency switching currents.
the pre filter capacitor connection loop to inductor & MOSFET source should be as small as possible.
The value...
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