Akula0083 Light No3 - Dual TL494

[d3x0r]

I haven't gone through JB's schematic.  What I can tell you is what I have:  If M1 and M2 turn on simultaneously then as you show L2 and L3 the coupled flux cancels out reducing the effective inductance of each winding to 1/20th of what it is when just one or the other MOSFET turns on.

Okay... but what's the difference... between 2 coils in series and 2 coils allowed to flow at the same time... on the same core?


There are differences.  The L1 (pickup coil) is attached to a huge cap... becuase that's its purpose... to move from high potential to ground... the 3 diodes are just lower resistance and can be simplified


instead of pnp and postive bias I used mosfets and positive going clocks; the voltage sources between 0 and + and absolute for simulation purposes so there is no requirement for pulldown resistors etc.

(and maybe you're referrning to a wrong diagram... do you mean schametic 1 or schamtic 2 that the coils are mutually cancelling?)

[d3x0r]

or maybe... sharing a common source or being chained?


Edit:
google doc share of lt spice realized that's not the best way to share things; but I tried attaching a .asc as a forum attachment and it denied it... sorry it's so much work; but falstad doesn't support arbitrary inductor coupling


I added a power source with a enable for the first part of the run; so it's like apply battery, remove battery...


added some caps around L1 that allows a curent to flow in L1... don't know why the diodes kill any current....

[MarkE]

When two coils are on the same core it forms a transformer.  In this case it is sort of a good thing because otherwise there is nothing to clamp the drain voltage for each MOSFET when they turn off.  But if both MOSFETs turn on at the same time each winding looks like a shorted secondary to the other winding.  The effective inductance is reduced to 1/K the original.

[d3x0r]

Sure; but it's more like this...

[d3x0r]

re: why?


Lets start with just the 2 coils...
1) inductance is 50uH
2) inductance is 100uH


voltage increase is 1:1.414  (1:sqrt(2))


if simultaneously enabled, the inductive reactance is of 2 is 2 times that of 1... so the current should flow....


if there was 1amp ... 1/3A in 2  and 2/3A in 1 ...
so the current increase in 1 is greater than the current increase in 2... and because the resulting voltage is also higher than the source voltage, it is quite likely that coil 2
would flow backwards...

crazy. 


Edit: L1 coils was backwards; it's normal forward induction was against the diodes... works a little better reversing L1
works better also if inductance of L2 and L3 are the same in the simulator...
Added some diodes so high voltage doesn't build up against the mosfet... well I had some other diodes that I removed too; did have diodes in pointed to the mosfet so the current would only flow the one direction; instead of leaking backwards through the mosfet in case of reverse induction....*shrug*