Flyback with TNY379
Posted by: Hans01
on
Hallo
my flyback converter has very high voltage peaks (250V). How can i avoid that. The input voltage is 300V and the output is 24V at 0,67A. It's an RM6 coil with a winding rate of 36:18.
Thanks
Comments
Would you please provide more information such as the waveform, where you've taken the waveform and load condition?
Regards,
PI-Scotty
The waveform is on the DS- voltage at tny379. The transformer is an RM6 coil with N48. Input voltage 80V, output voltage 24V at 5,7W.
sorry to butt in...i thought you said your input volts was 300V?
Anyway, i recognise those bad-boy spikes anywhere.........my first SMPS electric shock was from the heatsink connected to the drain of a mosfet in a flyback....my spikes were going up to 1400V!......and the elecric shock felt like an intense heat!...i turned the smps off, felt the heatsink, and it was stone cold!
anyway, those spikes are worse when you have a lot of leakage inductance......also, you can reduce them by having an RCD snubber ....or by snubbering across the fet
The voltage spike at turn-off is mainly caused by the energy stored in leakage inductance. You may try to change the transformer structure and to minimize the primary loop area of your layout. A split primary construction may be helpful. Half of the primary winding is placed on either side of the secondary (and bias) winding in a sandwich arrangement. Please also make sure your clamp circuit can limit the Vds below 650Vdc to avoid the damage of the device.
Regards,
PI-Scotty
The primary inductance is 423µH and the leakage inductance is 27µH.
The input voltage is at the moment 100V. At 300V, there are problems with the heatsink, too.
How can i calculate an RCD snubber?
