TOPSwitch-jx on no load
Hello,
Do you have any demo board of an isolated, offline TOPSwitch-jx SMPS (of at least a few Watts max load and say 5V output ) which can power itself via its auxiliary winding even when the secondary is completely unloaded?
when the TOPSwitch-jx goes into multi-cycle-mode, it is bursting on/off and this would require iterative auxiliary coil design to get decent auxiliary output across the load range.........and variability of auxiliary output depending on the tolerance on the trafo leakage.
-then there is the problem of peak-charging of the auxiliary to the leakage spike.
A demo board of this would be very intersting.
Comments
Thankyou for your advice and link to DER-247, and your suggestion of putting the auxiliary winding next to the secondary winding, and away from the primary winding.
Unfortunately, such a winding configuration will increase primary to secondary leakage inductance, which is very undesirable due to the reduction in efficiency.
No because the ideal arrangement is primary-secondary-bias, which actually minimizes primary to secondary leakage inductance.
OK, but on page 46 of DER-247 it shows the secondary AND bias windings sandwiched between the two primary layers.
-this will mean more primary to secondary leakage than if it was just the secondary sandwiched between the two primary layers, and the bias winding put on the outside.
The main demo board, RDK-242 (30W)
http://www.powerint.com/sites/default/files/PDFFiles/rdr242.pdf
on the main Topswitch-JX page, http://www.powerint.com/en/products/topswitch-family/topswitch-jx
does what you ask. You will see in the report that they regulate down to zero load, and that the C pin is powered from the aux winding.
The DER-247 (20W) is another such example.
http://www.powerint.com/sites/default/files/PDFFiles/der247.pdf
The trick is to wind the bias winding next to the secondary winding, and away from the primary winding.
In order to search for all the TOPSwitch-JX power supply design reports, go to the design example page:
http://www.powerint.com/en/design-support/reference-designs/design-examples
then in the top, click the column title "Product Family" to sort by product. It is now sorted in ascending order. If you click it again, it will be sorted in descending order, and TOPSwitch-JX will end up at the top of the list. On the right, under the column "Doc #", will be the direct links to the reports.