edanderson
Well-known member
leakage inductance comes from physically separating the field spaces of the primary and secondary windings. i'm not an ancient elder, but i think the only thing i can think of that would fit your criteria has already been mentioned by mark:
when you had success with an EI transformer, did it use a two chambered bobbin? if so, that type of separation is most analogous to a toroid wound in two sectors -- all primary on one side, all secondary on the other (different gauges), looking similar to a common mode inductor.
the leakage inductance would act similar to a load, so the turns would have to be adjusted to still achieve the desired output voltage, etc.
while toroids are generally more efficient than EI core designs due to better utilization (the winding covers the entire magnetic path of the core, and there is no gap), you would essentially be reducing efficiency by increasing the leakage inductance. not saying you couldn't make a toroid that would work better than an EI design of the same core size, but there's no free lunch -- you'd still have to use a larger core and/or more turns than a stock low leakage toroid transformer.
in the end, PRR is probably right that your best bet would be to use a higher VA and higher secondary voltage EI core transformer. unless you're willing to make significant qtys, a power toroid wound this way will be prohibitively expensive due to the unusual setup. and the improvement may end up being marginal anyway.
my best guess, hope that helps...
ed
marik said:...using each half of the core for respectively Pri and Sec windings...
when you had success with an EI transformer, did it use a two chambered bobbin? if so, that type of separation is most analogous to a toroid wound in two sectors -- all primary on one side, all secondary on the other (different gauges), looking similar to a common mode inductor.
the leakage inductance would act similar to a load, so the turns would have to be adjusted to still achieve the desired output voltage, etc.
while toroids are generally more efficient than EI core designs due to better utilization (the winding covers the entire magnetic path of the core, and there is no gap), you would essentially be reducing efficiency by increasing the leakage inductance. not saying you couldn't make a toroid that would work better than an EI design of the same core size, but there's no free lunch -- you'd still have to use a larger core and/or more turns than a stock low leakage toroid transformer.
in the end, PRR is probably right that your best bet would be to use a higher VA and higher secondary voltage EI core transformer. unless you're willing to make significant qtys, a power toroid wound this way will be prohibitively expensive due to the unusual setup. and the improvement may end up being marginal anyway.
my best guess, hope that helps...
ed