Leading edge current limit
Hi,
My problem is my TNY278 thermally shuts down upon upon running on high voltage. The series MOSFET is also rather hot. At low voltage, there's no problem.
I've noticed the leading edge current is very high.
Local PI engineers have suggested cutting back parasitics but the PCB trace as it is now is already rather "tight".
I'm getting another transformer done with tapes between layers to cut back on winding capacitance. Yet to see how bloated up is the leakage inductance then.
The output circuit uses a Schottky diode. Adding a snubber across the diode only helped to clamp the ringing (~30MHz). The heating and leading spike remains high.
Some parameter below:
a) maximum Vds = 500V
b) Idrain cutoff = 400mA but cuts back to 280mA when device heats up.
c) leading edge transition time = 100 - 150ns
d) leading edge current = 1 - 1.2A
Evidently the leading edge current is unacceptably high, breaching the device maximum limit of 1.024A spike over 400V.
Question: what else can I do to reduce the spike leading edge current?
Comments
I'm not using any secondary winding.
The secondary circuit uses a Schottky barrier diode.
This problem's solved by reducing the winding inter-layer capacitance and cutting down on the Y2 cap values by half.
ok. I assume that you cut inter-layer capacitance by adding a layer of tape between two layers... Is that correct?
Yes, I added an additional layer of tape between each layer.
what diode are you using on the secondary and bias windings?
Pls send me your schematic so I can comment.