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Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Ash Small wrote ...
Yes...but the diodes prevent the output going negative, so the output can't oscillate. (at least as I understand it)
yes but wont it bounce up and down with out going negative? i doubt very much that our outputs are perfect square or triangle waves,...i bet theres significant distortion from the ideal. and thats what im asking about.
Does this make sense or is this all crazy talk on my part?
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
I can see that, due to the inductance and capacitance of each stage, there could possibly be some internal oscillation, which would only pass the diodes on the positive cycle (I'm only guessing here), but the diodes would prevent ringing in the 'normal' sense i.e. an AC flyback would ring (if not connected to a diode), but a DC flyback can't ring in the accepted sense.
That is my understanding, but I'm not saying I'm correct (I'm a relative newbie as far as this stuff is concerned).
Registered Member #3610
Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506
The output looks like very sharp spikes along with a lot of random looking noise. You can measure it approximately by holding a scope probe near the operating flyback. You don't have to electrically connect it.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
For the resistively loaded case, the output is just a more heavily damped oscillation. Maybe more than critically damped, so you see no oscillations at all, just a "spike that tails off" as someone said.
With the diode split, there will still be oscillations, you just won't necessarily see the negative half-cycles. I say necessarily, as the diodes have recovery time, capacitance, and the secondary structure has stray capacitance, that will couple voltage to the output even if the diodes don't conduct.
(Corollary: if you hook up the primary backwards, the negative half-cycles are the positive ones, if you see what I mean. So you may blow the diodes)
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Steve McConner wrote ...
For the resistively loaded case, the output is just a more heavily damped oscillation. Maybe more than critically damped, so you see no oscillations at all, just a "spike that tails off" as someone said.
.
Why does the spike 'tail off'?....is this due to the internal capacitance of the secondary?
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Conservation of energy: The spike can't last for ever because the energy stored in the inductor is finite. Therefore, it must end somehow.
Ohm's law: The spike can't end suddenly, because the rate of energy absorption by a resistor is proportional to the square of the voltage across it. The less energy remaining, the slower it gets used up.
Therefore the spike is the classic waveform produced by a shock excited RLC circuit, involving some combination of oscillations and/or an exponential decay.
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Flybacks and Waveforms...
