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1
Repair / Re: HP 'Bill West' leaf springs: where do they go to?
« Last post by TERRA Operative on Today at 11:19:00 am »
Take all the panels off the instrument and give it a good shake in all directions and orientations until your arms hurt, then cross your fingers and close your eyes when you power it back on. :-DD
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Thanks for bringing this up. I know what you mean.
But if i put in values of
Stray C (interwinding) =10pF
dV = 400V
dt = 20ns

.

The 3 A came from the 300 kV/us figure you gave earlier. You gave no other numbers earlier, so I worked with that. You never mentioned anything about the actual numbers you were expecting, but those only yield 20 kV/ us. Why are you even bringing up CMTI if your real worry is something else?

By the way, many engineers seem to be able to use high-side driver ICs successfully, though they do have their gotchas. IR211x has been around for decades, and there are many more choices today. Careful attention to layout prevents a lot of negative voltage issues.

FWIW, it's been a few years since I worked above 200 V, but I had good luck with SiLabs (now Skyworks) Si827x series drivers at the time, switching GaN FETs at ~350 V in about 3-4 ns.

John
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Just use the EasyPower software and the normal SPD3033X firmware (not the -E firmware) as usual.
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Microcontrollers / Re: CH32V003 Flash like Eprom
« Last post by Atlan on Today at 11:10:20 am »
The standard procedure for programming is erasing the chip before programming.  I prefer this option because it happened to me on other uP that the program did not work correctly.  An external programming program allows selection without erasing, but.  I don't want to use that.  Programming directly from the IDE erases the flash before programming.
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But the client can be disassembled anyway and any private key extracted from it.

Easily, but that is why you use unique private key for each client, so that you can't buy a product and then pretend to be another customer. But yeah, if you break in or otherwise gain physical access to the heating controller, then you can read out the private key, and pretend to be that single heating controller. This is usually the level of risk we can accept, because one could also just replace the physical heating controller with any malicious device (which could connect to another server completely).

In my opinion, authenticating the client is important so that you can't pretend being another customer, but your mileage may vary.
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Manufacturing & Assembly / Re: Vapor Phase reflow oven
« Last post by woody on Today at 11:04:52 am »
Another option is to simply tilt the whole oven so the drops on the lid slide to the side. I would also make some system in which I can squeegee it directly back into the oven without an extra plastic container. Every extra surface that gets wetted will cause needless extra liquid loss.

That is actually a bad and possibly dangerous idea; the layer of Galden in these ovens is really only a few mm. By tilting it part of the bottom might no longer be covered in Galden, which might heat it beyond safe temperatures. For this reason I placed my oven using a level.

You cannot get away with filling it with extra Galden to still cover the bottom, as more of the medium slows the process time considerably. Longer heating, longer cooling. And, as we all know, it is bloody expensive  :D
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Metrology / Re: Help me choose buffer circuit for LM399/ADR1399 7V to 1V
« Last post by qat on Today at 11:04:08 am »
Presuming it needs to not significantly degrade the stability of the reference, the approach I generally take is to have extra footprints for discrete resistors in parallel with each leg of the divider. At the ovenized reference level of stability, I would say that potentiometers are generally frowned upon, though if you are using one with a trim range of perhaps 100 ppm, you could probably make a reasonable case for using it. It seems like your circuit is probably part of an autocalibration block, so you could probably just deal with deviations from nominal in software. I think the conventional wisdom on this board would also be to use something like a NOMC 8-resistor array as the divider. I don't know offhand the best way to do 6:1 with that, but I think that for statistical averaging to be most effective, something other than the obvious 6 in series : 1 would be best. Perhaps three in series for the upper leg and two in parallel for the lower leg with the resistors interleaved would be good. You probably don't want to go higher than 500 uA divider current because the Joule heating tends to worsen the stability of the divider and make it more susceptible to thermal EMFs.

Many of the op amps one would normally use for buffering a small voltage with minimal error have current noise that could be problematic, especially if you have the inputs of multiple op amps connected to that node without a buffer. If you are using an autozero amplifier, you will probably want to bypass the lower leg of the divider with maybe 10 to 100 nF (C0G) as the switched inputs have lower current noise when there is some bypass capacitance. Depending on your target bandwidth, you could add some more bypass capacitance, but at <10 Hz you usually just deal with it.

Less obviously, you need a good way of measuring that voltage if you're going to trim it without needing to hold the test leads, preferably with things as close to fully assembled as possible. Through-hole test points where you can solder magnet wires (or similar) are good. Keep them next to each other to make sure the junctions experience similar thermal gradients or just use the footprint for a 2-pin 50 mil pitch header.

In my scenario, the reference voltage will regulate the current flowing through a laser diode and manage its temperature. It's practical to adjust the reference voltage using a potentiometer to fine-tune the current, thereby controlling the laser's wavelength. Since laser's characteristics can vary significantly, I'll probably need to adjust the reference voltage output by approximately 5% (equivalent to 50000 ppm ;) ). I'll incorporate your suggestions to optimize my design and conduct simulations and calculations to see what performance I'll actually get.

For calibration I'll use SMT test points or pins for attaching leads for calibration using a 6.5-digit multimeter to achieve a target voltage of roughly 1V (or whichever reference voltage I ultimately select). The final calibration will utilize an optical spectrum analyzer for precise adjustments. :)
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The AD8628 is a relatively slow OP-amp and  I don't see the drive strength much better than directly the ADR4540 reference.  The ADR4540 seems to have a class B output stage and may get better when there is some actual load current (e.g. maybe in the 0.1-1 mA range as a resistor to ground). At least it can handle a relatively large capacitance with no problem. I would drop the AD8628 and diretly use the ADR4540. The INL from added capacity at the LTC2400 ref. inputs is a bit tricky - it can get better with a relatively large capacitance of some 1 µF. One usually wants quite some capacitance to provide the current spikes. With no capacitance it depends on the driver side - this can be better or worse and it hard to tell.
This is a general problem with SC based SD ADC chips: the INL depends on the reference input and signal driver, it is not just a function of the ADC chip.
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General Technical Chat / Re: think your lab is bad?
« Last post by Geoff-AU on Today at 11:02:35 am »
Electroboom-ish entertainment.  I'd never be that desperate to need to solder something.

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Metrology / Re: Low noise chopper and DIY nV meter
« Last post by macaba on Today at 10:57:08 am »
Curtis,

I tend to think that with any kind of ultra precision instrumentation project, a descent into madness is inevitable and perhaps even desirable! A certain kind of manic ultra-focus is sometimes needed at this level as a lone developer.

With the inputs of the TMUX4053 shorted (U32 if you have the schematic handy), by my reckoning, I should see about 31 nV/rtHz (28 from the diff amp block at gain of 2, and 13 from the AD4030 (it is a factor of sqrt(2) quieter than the AD4630). I actually see 58 nV/rtHz at 2 MSPS, going an order of magnitude higher at 500 kSPS.

Your reckoning seems about right to me, and your 58nV/rHz (assuming no calculation error) is further proof - I also saw an approximate doubling/tripling of noise until I fitted the correct charge kickback filter values. It seems the precharge circuitry on these ADCs simply reduce, not eliminate, the issue.
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