Re: SMPS question

On Wed, 21 Sep 2005 08:56:58 +1200,
Terry Given <my_name@xxxxxxxx> wrote
in Msg. <wI_Xe.13255$iM2.1117632@xxxxxxxxxxxxxxx>

> at such low voltages I would use a diagonal half-bridge primary - a
> switch at either end of the winding, one to +30V, one to 0V. And a pair
> of (schottky) diodes, one to 0V (at the +30V end), the other to +30V.
>
> drive both switches simultaneously. Both on = energy storage. both off =
> energy transfer. the primary winding voltage is now clamped to the +30V
> bus, by the two diodes. Voila, no spike and almost no losses.

Sounds good; I'll consider it.

> sandwich the smallest winding (fewest turns) between the two halves of
> the largest winding (most turns). This'll give you a significant
> reduction in leakage inductance, and allow you to use thicker copper
> (the number of effective layers halves)

I must confess that this doesn't make sense to me. The way I understand
it is: Leakage inductance is created by flux that goes through one
winding but not fully through the other (which makes it synonymous with
poosr magnetic coupling). In other words, the portion of flux that the
primary created but that doesn't go through the secondary will obviously
not be reset by the secondary (and be put to good use on the load side)
but will cause voltage spikes on the primary side that need to be dealt
with. In the "diagonal" setup that you described, it will be fed back
into the primary-side storage cap.

But before you go into explaining what "effective layers" means I really
should read a book.

> all first-order switchers have an L and a C. in a flyback, L=Lmag.
>
> otherwise, the primary switches see a capacitive load, with either dV/dt
> or R setting the peak current (ignoring leakage....)

Ooops .. I should have thought of that myself.

> Keith Billings Switch Mode Power Supply Handbook, followed by Abraham
> Pressmans Switching Power Supply Design. both McGraw-Hill

A lot of money for a lot of knowledge.

Thanks,
robert

.

Relevant Pages

  • Re: Two-speed motors with inverters (again)
    ... winding is switched damaging whatever is used in the output stage. ... of the switch? ... change in impedance between the supply cables and the motor windings. ... They will limit the output voltage to no more or less than the DC ...
    (uk.rec.models.engineering)
  • Re: Two-speed motors with inverters (again)
    ... winding is switched damaging whatever is used in the output stage. ... of the switch? ... change in impedance between the supply cables and the motor windings. ... They will limit the output voltage to no more or less than the DC ...
    (uk.rec.models.engineering)
  • Re: Need Help with my IJ
    ... hold winding in the coil trying to activate the diverter. ... So with the diverter tested and confirmed working, I'd have to say the opto ... entrance switch. ...
    (rec.games.pinball)
  • Re: Need some electrical know-how
    ... switch to the saw. ... A single-phase induction motor with only one energized winding will not ... or the capacitor can be bad as well. ...
    (alt.home.repair)
  • Re: Clue me in on this.
    ... direction despite the winding mismatch. ... Capacitor start motor. ... Capacitor good 2 windings. ... If there's no start switch, it's a permanent split capacitor, or PSC motor. ...
    (sci.electronics.repair)