Recent Posts

1

Metrology / Re: measuring 100mA current source with a better than Keithley 2000

« Last post by The Soulman on Today at 05:19:52 pm »

Your best bet is the Hioki on the 120mV range in 7,5 digit mode (is the sample rate high enough?) with an external 1 Ohm shunt.
100mA reads 100mv and the least significant digit is 10nA, speed and accuracy may not be great.
Power loss in the shunt 0,1V*0,1A=0,01W or 10mW, easily manageable.

You could add a op amp to the above and amplify the shunt signal 10x or 100x  for 1nA or 0,1nA resolution but you would need some range switching in that case.

What is the duration of your current pulse and how accurately do you need to measure it?
And why do you need that much resolution?

 

2

Test Equipment / Re: Siglent SDG6000X changing duty cycle glitch

« Last post by H.O on Today at 05:19:27 pm »

I don't see it mentioned in the revision history in the file tautech linked to but why not try updating just in case.
I know it does not help but my Rigol DG4162 acts in the same way, very bad indeed when testing locked antiphase PWM motor controler. Really annoying on an expensive instrument. It's been discuessed here before and IIRC other DDS type generators do it too while some don't.

On the SDG6000X, is it possible to modulate the dutycycle using either the other channel or external input and if so, does THAT work as one would expect?

3

Test Equipment / Re: RuiDeng Riden RD6006 DC power supply

« Last post by csvke on Today at 05:10:19 pm »

Is there anyway to use the Riden RD6006 flashed with the great Unisoft firmware with Sigrok? I would like to do power logging

4

General Technical Chat / Re: GFCIs and Treadmills

« Last post by soldar on Today at 05:08:57 pm »

I cannot imagine how it can be legal to sell a machine that trips a GFCI. 

I cannot imagine how it can be technically justified. Sounds like crap with insufficient insulation.

In Europe the code requires whole house protection so you could not use it.

5

Repair / Re: IWATSU oscilloscope Cal signal square wave showing as ramped / curved signal

« Last post by tggzzz on Today at 05:05:42 pm »

I don't know why you guys think I don't have another oscilloscope lol. Is it the female name?  I've just never messed with an analog scope before is all, and I'm used to using newer stuff that "just works"

Like I said my other probes are similar (Agilent 12pf) and I know the lecroy probe works fine.

Anyway I just tried a wire going directly from the connector to the CAL output and the waveform looks the same so I guess the problem is with the oscilloscope itself.

All standard *10 10Mohm probes should be re-compensated every time they are moved to any different scope. In theory the compensation ought to be checked when moved to a different input on the same scope, but I don't know anybody that bothers.

I compensate them every time but I didn't realize that I had to spell out the fact that I know how to do that and that it was the first thing I tried, and also the entire reason I hooked up the probe to the CAL signal to begin with 

Anyway thanks to people providing actually helpful information instead of repeating the absolute most basic stuff and assuming I know 0 at all.

That could have easily been avoided if you had given the relevant information in your first post. Several people have pointed out that lack of information, and you have ignored all of them. Perhaps paragraph 3 of https://entertaininghacks.wordpress.com/library-2/good-questions-pique-our-interest-and-dont-waste-our-time-2/ might help in the future.

Anyway, won't spend any more of my time helping you in the future.

Literally in the title of the thread it says it's the calibration square wave signal, if by help you just mean mansplain and assume I don't know anything then I don't need your help. If you read the things I posted you would see that I eventually provided all of the relevant information yet you still tried to mansplain to me how you're supposed to calibrate the probe every time.

Other people though have given me useful troubleshooting info.

And yes I'm being snarky because I always get treated this way and it gets tiring. I am a real engineer and probably know a lot more than you think. I need to just stay off of internet forums. Never argue with a guy with 19000+ posts 

I have many calibration square wave signal sources; most are not part of a scope.

Yes, you did eventually provide all of the relevant information. Given that you didn't post it initially, and the very basic question, the reasonable initial presumption was that you are an inexperienced beginner. I'm not the only one to think that.

Why do you think "19000+ posts" is relevant? I don't. Rather than "stay off of internet forums", I suggest it would be better to use them effectively as a communication mechanism.

6

Beginners / Very long trace left unconnected at one end... is it bad?

« Last post by Saimoun on Today at 05:05:09 pm »

Hello!

I'm kidding, I know it's bad 
But I'd like your help to find out how bad! The circuit is very simple:

MCU pin -> 1.8k res -> NPN -> Collector pulled up to 5V with a 820R res and emitter to ground.
(see attached picture as well)

Then MCU is used to switch the voltage between 0 and 5V to send a digital signal.

The problem is the signal is also routed to a very long trace (about 25cm), reading about it online it seems that with 25cm, only frequencies above 300MHz
will start to be an issue. Would you confirm or is there more to it even at low frequencies?

I'm trying to calculate the frequencies of the 5V signal. The MCU datasheet gives the max rise/fall time (see attached), say we estimate it at 20ns. Looking up online again, I found that the highest frequency is about 350/20 = 17.5MHz. This is probably slowed down by the 1.8k resistor at the base of the NPN anyways, so... it looks everything should be fine?

Thank you!

7

Repair / Re: Datasheet for Nichicon SE series ?

« Last post by fenugrec on Today at 05:03:55 pm »

Might try on archive.org or bitsavers, sometimes you can find scans of old catalogs.
Looking at the schematics where it's used will give a clue as to the important characteristics.

8

Beginners / Re: RS232 intermitted issue

« Last post by Retirednerd2020 on Today at 04:54:27 pm »

Serial configuration as others have suggested, and:

Look at the serial signals both ways with an oscilloscope and measure the bit rate both ways.  Do they match?  I have seen bad DUT clock (mis-configured or wrong crystal or other problem) cause serial issues.
With a short cable ~3-12 Feet (1-4 Meters) , I've not had issues with 115,200 Baud if the bit-rates are within/near what they should be.

9

Projects, Designs, and Technical Stuff / Re: LM5145 Inductor keeps heating up

« Last post by mag_therm on Today at 04:51:37 pm »

Is that powder? That's big even for laminated iron.  What control scheme did you choose?

Tim

My core is a surplus 3C85 double C . Outside dimension about 4 inch by 4 inch,
I made two core tubes of brazed 6160 with a gap and grounded. Two windings each of 2 by 18 G in parallel, connected in series to give 44T.
The temp rise was within Class B on 20 A test.
The DC converter has no base frequency filter caps, the battery equivalent C gives a double pole at less than 1 Hz I think.
There is a pi section RF filter with a small lossy iron core at output.
One reason the inductance is so high, is that the 13.8V load ( ham radio) is often less than 3 Amp,
If the load current in the choke becomes discontinuous the regulator is not stable.
Volt Error amp is type 3

My output filter with maybe -50 to -60 dB attenuation in proximity to HF radio is very different to MB's present design.

I see that the LM 5145 data sheet calls for L1 giving  30% ripple. But at 1 MHz I wonder if practical.
I think the track inductance + ESL of filters (total 100nF)  might be 10% of the L1
with resulting high ripple at 1MHz base freq.
And the inductor turns will be heated by that 1MHz ripple of 6 Amp; reference depth is 72 micrometre giving poor copper utilization.
Maybe Litz would be needed. Outside of my experience, but I think the eventual inductor will be physically much larger than his photo shows,
and possibly the 30% ripple current recomedation will have to be reduced, and maye NiZn ferrite used.

10

Projects, Designs, and Technical Stuff / Re: LM5145 Inductor keeps heating up

« Last post by trtr6842 on Today at 04:50:05 pm »

Inductor datasheets are notoriously sparse on core loss information.  Coilcraft has one of the better tools.  I plugged in your converter parameters into their core loss comparison tool with the XAL1060-122.  Its a similarly sized inductor and it's showing 3W of core + AC winding loss at 42Vin, 12Vout and at 1MHz switching frequency.  I suspect the losses in your inductor are at least that or even higher given the fact that it's saturation current is even lower than the coilcraft part.

Try running your converter at 15Vin and 12V out.  That will cut the core loss way down (8% of whatever you're getting at 42Vin).  This should buy you some time to actually scope out the "SW" node, output voltage, etc.  If you can get that scenario to work, then you can start bumping up the input voltage and you'll see what happens.  Keep records of input and output voltage and current and you'll end up with a good idea of how the overall converter losses change based on those parameters.

I think you're way more likely to have success if you reduce your switching frequency to 150-300kHz.  You mentioned TI's Webbench designer, if you look at all their suggested designs for 42Vin and 12Vout they are mostly in that range.  Core and MOSFET switching losses will be way more manageable.  You will need to increase the inductance, get the 4.7µH and 10µH versions of that inductor and give them a try.  You won't be able to get 20A out of them, but it should let you at least get this design to do something and will help you learn as much as possible for the next revision. 

I'm afraid there's no magic bullet that will save this design as is.  You might be able to find a much taller inductor that will get you closer to the design goals, but my guess is that part will need to grow significantly.

You can also look into winding your own toroidal core inductors, that could be good for prototyping and figuring out what is required to reach your design goals and select an inductor for production/end use.