It worked, first time.
That's the forced-PWM spread-spectrum version of that LMR38020 high-voltage switcher chip. It sees 48 volts in that circuit.
The spread-spectrum makes a serious amount of jitter, but it doesn't seem to make much noise on the -24 out. They must do some clever spectral shaping, vaguely something like 2nd order delta-sigma or something.
That red feedback wire could pick up switching noise from the coil field. Better keep it away from the switch output wiring.
Did you try teasing it, loaded, with slow rising input? I've blown some inverting circuits that way.
Arie
Nice. I wish I could dremel like you do! Ed
Take another look. I did some tuning.
It runs much better at 800 KHz, and with some ESR in the output cap. It needs freeze spray to keep going, but there's no heat sinking on my proto board.
After a lot of dumb finger-fumble incidents, I haven't blown the chip!
That red wire doesn't seem to matter. That is a (semi) shielded inductor.
I tried a slow powerup; seems OK. That chip has internal soft start. The input impedance of this switcher is negative, so it could theoretically cave the input supply on startup. I need to be careful about that.
So far, so good.
Thanks for the warnings.
John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics
I use a carbide dental burr, and a lot of practice. I'm naturally steady too, which really helps. The Mantis viewer helps a lot too.
I was talking to the guy who repaired my retina with a tiny pair of tweezers. We both hold our breath when we're carving.
John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics
I had a vasectomy reversal and the surgeon took beta blockers to slow his heart and made the stitches between heartbeats!
I already take beta blockers!
I was awake and seeing everything going on (and talking to Dr S and the nurse) when he peeled the top layer of cells from my retina by hand with tiny tweezers. The nurse showed me the teeny tweezers afterwards and we discussed our favorite english literature. She's done the whole P&P Pemberly tour. I turned her onto Lord Peter and PG Wodehouse.
Great light show.
Mammalian retinas make no sense. They are built upside down, complex, fragile, and have entire layers that they don't need.
I have a friend who got prostate cancer and paid a bunch extra to have robotic surgery, to remove the cancer but leave everything else working. Eventually robots will do the really delicate surgery.
Got kids?
John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics
Yes, two daughters, vasectomy was after the last one was born but post vasectomy pain developed and was horrific. First doctor offered to strip out the nerves, I opted to fix the cause instead. Was awake though out the procedure under local.
They make perfect sense to me. Mine work fine. We're keeping an eye out for glaucoma as it runs in the family.
Admit it's weird that the light-sensitive ends of the cells point
*away* from the light, while the wiring runs over the side from which the light comes in. At one point, all these nerves have to get to the brain somehow, so there is a hole in the retina where everything has to pass through, causing a blind spot.This would have been a design blunder, if the eye had been designed.
Jeroen Belleman
What you see is constructed by your brain. You think you see in full detail over your field of vision but your eyes don't, your brain does it. The brain finds it easy to paint out the blind spot. Keeping the wiring in place through one exit hole seems perfectly sensible to me. All the layers in the retina have a specific function.
In other critters, the blood vessels are behind the retina and nail it to the back of the eyeball. Our blood vessels are on the inside and block light and do not attach the retina. As people get older and the vitreus thickens, a little shock can yank the retina off the back of the eyeball. Fortunately, that can usually be fixed these days and the retina can then be spot welded to keep it in place.
Retina detatch is a common side effect of cataract surgery too.
If this inverted design makes sense, I don't see why. Or how it would have evolved incrementally from its ancestor structures.
John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics
All perfectly true.
Nature has no need to make sense to us.
Semiconductor imaging photosensors for cameras were first designed that way - front illuminated sensors.
Sure, but I don't care how the brain hides the deficiencies, the thing is still backwards. It would have been so much easier if the wiring had been *behind* the layer of sensors. Better sensitivity, nothing in the way of the entering light and no blind spots.
Jeroen Belleman
Easier for who or what? Nature isn't a human camera maker.
I can't find a recent article I read about why nature did it the way it did but attenuation of incoming light (so we don't have issues glancing at the sun) was one of them.
Fine, as long as there isn't a tiger or a motorcycle there.
John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics
It may be a bit more complex than that. The nerves have all the strength of jello, so it may be better to fix the sensors to something solid, so the alignment can remain fixed.
Joe
That's the typical post-hoc reasoning fallacy. That doesn't work.
Jeroen Belleman
Well, there are animals that have it the right way around, and their vision appears to work at least as well.
Jeroen Belleman
Have something to add? Share your thoughts — no account required.
Ask the community — no account required