We have an offline flyback currently using the onsemi NCP12XX range of controllers that we would like to convert to a Topswitch-jx design, because we believe it will be easier to maintain and modify the design within the Power Integrations 'Development system'.
However, does our primary di/dt mean that we can't use Topswitch-jx?
[U]The Flyback spec. is as follows:-[/U]
Vin = 85-265VAC
Vout = 25V
Pout = 32.5W
F(sw) = 66kHz
Discontinuous Conduction Mode
NS/NP = 0.4535
L(pri) = 270uH
We see that our peak primary current of 2.1 Amps means that we need to use the TOP266 part..
However, on page 27 of the Topswitch-jx datasheet, it says that the peak current level of 2.55 Amps (for TOP266) depends on the primary di/dt being [U]530mA/us.[/U]
This seems to be a problem because in our design, the primary di/dt is [U]1370mA/us[/U] (when at 265VAC).
In fact at any DC bus voltage above 145VDC, our primary di/dt is above 530mA/us.
So does this mean we cannot convert this particular design to a Topswitch-jx design?
(I appreciate that we could re-design it to get a lower primary di/dt but that would then mean needing to re-do the transformer)