Still trying (and NO LONGER failing) with the LM2588... 5V -> +/- 12V

[Skimask]

I would put a pot on the frequency input and graph the efficiency across the frequency range.
You'll get better efficiency if you tune the frequency to match your transformer.

I'm gonna give this a try.  I'm using the recommended transformer, not the exact recommended output cap's or input cap's.
Couldn't hurt...

[Skimask]

Ok, first quick look at changing the frequency of the LM2588...

100k pot on pin #1 (freq adj / shutdown), 'scope hooked up to pin #5, the switch pin.  Alligator clip wire set is M.I.A., so couldn't get reliable current measurements.  Either that or power it off the PSU and read the current from the display.  Give me something to do tomorrow.

With the pot dialed around to 100K, sloppy waveforms on the 'scope.  Barely recognizable 100khz signal coming thru.
Rotate the pot (decreased resistance) and I can see the frequency increasing,  until I get about 3/4 the way around, and SNAP...the switch waveform gets clean, some bouncing, not much.
Not sure if that's a function of the iffy hold-knob on the 'scope though.  Could be that's the perfect frequency and timing for the hold-off itself.  And if I rotate the pot any farther, it goes into shutdown, just like it's supposed to.
Also, the frequency is about 208Khz at that "perfect point", a bit above the maximum stated in the datasheet, with "Rset" at about 8Kohm.

Even though I couldn't get a current measurement off the battery (due to missing alligator clip leads), while rotating the pot, the voltage on the output varies a few tenths of a volt, not much at all (cheap meter doing the reading for now), but more importantly, the A/C component of the output power starts out at about .6v at the lower frequencies and drops to about .1v when the waveform "snaps" into clear view at the higher frequency.  Spikes disappear, everything looks a lot smoother.  That might also be a function of the bandwidth at the input to the 'scope itself.  (Tek 2246A)
And, the regulator heat sink didn't get above 65C during this run, without a fan.  Before this, I had a 40mm fan blowing air across the heatsink to keep it from going into thermal overload shutdown @ >120C.

I'll take a video of the 'scope tomorrow while I'm messing with it.....if I get to it.

EDIT:  On another note, regarding current measurement on the meter.  Would I be better off measuring the current off the battery using the AC or DC mode?  Maybe put the biggest cap I can find across the battery pack leads?  It's not alternating current, but it's surely a varying current.  Maybe, since I'm using a cheap meter, in this case I'd be better off rather than trying to directly measure the current, I'd be better off measuring the delta of the current measured at the various frequencies.  For instance, I know I'm reading ~1.81amps using this cheap meter at 100Khz.  If I run the LM2588 up to 200Khz and the current drops to, say 1 amp, throwing out the effects of frequency on the measurement, I'll at least know I'm pulling ~.81amps less than before (and even that .81 amps probably isn't correct either, but less is less, a lot less is a lot less, and so on)...  I know I'll have the same problem using my bench PSU, current readout will vary, will the readout keep up?  will it average?  will it display garbage?  Won't know 'till I try it.

[Skimask]

Now I really feel like a dumbass...

C(comp) is supposed to be .47uf, e.g. markings should be 474, not .047uf (marking of 473)!

'scope traces on the switch, pre- and post- catch diodes, top of the load, Vin at the LM2588, are clear(er), not perfect, but resemble the waveforms in the datasheet now.
And more bonus points, the regulator didn't get above 60C during the 1/2 hour I ran it.

Used my power supply for juice.
4.6v @ 1.21 amps = 5.566 watts input
two rails of 12.8v @ 312mA amps = 3.9936 watts output
3.9936 / 5.556 = 71.9%
72% isn't the 90% the datasheet calls for, but wayyy good enough for me.

Also, the input amperage doesn't change by varying the frequency at pin#1 (freq adj), at least not as far as my psu shows (only shows down to 10mA).

So, dumbass award of the day goes to ME!

[Skimask]

More success -- ish...
Still not getting above 71% efficiency, but the circuit works.

Same circuit as before, same battery input, same 82ohm resistive load on each side positive and negative.

10000mah 4 cell D size NiMH battery pack, cutoff at 4v (1v/cell), started out at 5.1v under load, 1.1amps, ended at 4v under load, ~1.4 amps, 5.57 watts average input.
Continuous 12.8v at the output.  I could've ran the pack down to 3.7v before it cut itself off due to low input voltage, but I don't want to beat up on the battery pack too badly.
Ran 5 1/4 hours.  12.8v @ .312mA = 4 watts * 5.25 hours = 21 watt/hours.  Battery pack = ~4.4v @ ~1.21amps = 27.9 watt/hours...about 75% efficient.
Doing the math on the battery pack itself shows my run times just about match up to what I'm seeing.  Not too bad.

In the "real world", the maximum output load will be a DAC driven AC sine wave, so output current will average about 70% of the total, meaning that this 5.25 hours of run time should translate to about 7 hours of run time, assuming it's used for those 7 hours continuously.  Add in another 500mA draw from the rest of the circuit, drops the total run time down to ~6 2/3 hours.

I'm happy.  Now onto a switching regulator to drop the 4 cell pack down to 3.3v...

Thanks to all those that pointed me to good information/datasheets/white-papers/etc for tips, calculations, formulas, ideas (good and bad!), on how to properly design and set up switch mode power supplies in general.  I learned a crap load.

[Skimask]

Added a couple of PIC driven MOSFETs to the load to switch it on/off @ 100Hz, 70% duty cycle...
Added a 5W 8.1ohm resistor across the battery pack input for a "constant"-ish 590mA load...(simulating the rest of the circuitry that'll be in there)

Charged the battery pack..and BLAM...
6 hours & 45 minutes before the battery pack voltage dropped enough to pull the LM2588 out of regulation.
Not too shabby...