Oh, hey. I didn't see all the info krb686 posted in post #35 until just now.
...Reads...
Good stuff, you really do your homework. That's excellent.
I'm not trying to bad mouth, only making observations, but for Dan M to claim that simulators should not be used because they are inaccurate really shows his age, stubbornness, and doesn't do simulators the justice they deserve. Simulators have been bad in the past, but have made great strides in recent years. No real pro circuit designer doesn't at least have some simulator in his arsenal these days. Even if he was right though, and they were all unreliable, one would be paused to remember that simulators are rough drafting tools designed to flesh out a project quickly. Prototyping boards are great and definitely not going anywhere, but they are not nearly as fast as a good simulator is for getting the budding ideas out of your head. Doing things "out loud" does wonders for train of thought. You can usually spot a great deal of preliminary problems right away when you rough draft them a simulator. This lets you quickly figure out what the key parts of your project are. Though do keep in mind, in the end, one must always build a real circuit before being able to call it a working design. Because, as useful as simulators are, they certainly are not perfect.
krb686 said:
Are the simulators just not accurately programmed or are they missing something?
The main thing about simulators is that they can only ever do what you tell them too, and that usually means that they don't take into account every aspect of a real life circuit. The falstad sim is a great example. When you add a part, it will not include stray values, and wires are always 0 Ohms, even if these details might be critical to the real circuits performance. This is most apparent with the falstad sim when you do something like add a capacitor in series with power and ground without any resistance. Because a capacitor looks short to changing voltages, and the sim says there is absolutely no other resistance, the current can get up to a ridiculous level, something like a billion giga amps. The the sim usually kills it's self when this happens with a convergence error or something similar. In any case, just like you can model stray component values, you
can add them to a simulator manually as phantom components. I usually do this in falstad sim for things that have the biggest tendency to cause problems, mostly capacitors and ESR.
Anyway, moving on fro the simulator topic, Dan seems to also only want to consider the main transformer as acting strictly as a transformer. While it's true that it is technically a transformer, it's primarily acting as an inductor, just with an added feedback winding. The effect the secondary has on power and efficiency of the circuit is really only a secondary effect of what kind of feedback it is giving to the control circuitry. It's really just a sensor winding, and is not otherwise taking any part in the power conversion. But I think you already get that...
krb686 said:
...when Q1 rapidly cuts off, the inductor voltage spikes to whatever level, in that case 10.3V, necessary to push current through the next availabe path...
Yup, as far as I know this understanding is exactly right. If it was primarily working as a transformer, then a 1:1 ratio wouldn't produce more voltage than the input, but proof from real circuits clearly would show otherwise. What's really happening is the inductor is gaining energy from the current charging up the inductor "flywheel", then when the switch turns of, the inductors forward EMF is added to the input voltage, then pumped into the output capacitor. It's typical boost conversion at it's finest. With this in mind, I personally only play with the primary coil if I think the inductance is not right for some reason or another, mainly frequency related. I rarely would change it because of it's effect on the secondary.
That all being said, the ratio of the secondary to the primary *IS* important, as it controls how the feedback works. So in theory it can be taken advantage of. Though I may not necessarily 100% correct, I tend to think of it about like this.
Case 1: With higher base turns, you get stronger feedback while the device is oscillating, but because you tend to increase R1 as well, you get less drive during startup. Stronger feedback means cleaner switching, and thus better efficiency.
Case 2: With lower base turns, you get weaker feedback while the device is oscillating, but any transformer action allows for more current on the secondary. And you tend to have to lower R1 to get better feedback, which also leads to better low voltage starting.
Case 1 probably has the best applications for efficiency and power handling. Case 2 seems to be better for widening the operating range. With this in mind, I think Case 1 serves for better circuit improvement. In truth, there is not actually much
energy left in cell below 1V when compared to fully charged, so aiming for that is less useful. The real point of the circuit is efficiency.
krb686 said:
I'm curious why reality departs from theory in that aspect.
I'm not sure myself. All I know is my testing and simulating
did not strongly indicate that having an odd turn ratio was any better performing than just 1:1. But my gut tells me otherwise, as recently indicated above.
So krb686, if you do decide to play around with it more, Let me know if it does anything for you.