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91
Metrology / Re: [3458A] Yet another 3458 repair thread.
« Last post by e61_phil on Today at 06:23:12 pm »
A last sentence to the different ACALs:

I think one cannot compare the two systems (57xx and 3458) from metrology point of view, because the intention was completely different. No matter what is technical behind. The 57xxA CalCheck was intended to be a CalCheck. The rest of the instrument is temperature stabilized (where needed) to operate over the wohle range (+/-5°C) without any further compensation due to transfers.
The 3458A instead uses ACAL to compensate not only for long term drift. It is also intended to compensate for temperature variations. Therefore, even if everything is fine the CAL constants will move with temperature. That isn't a flaw, thats the whole idea here.


My wishlist for a new 8508A wouldn't include an ACAL like the 3458A does. If they would be able to get an ADC which is as good as the 3458As one. I would like to see a fast 8508B with CalCheck. That means keep all the expensive resistors and so on and then do transfers like the 3458A with the intention to report drift and not to correct anything.
92
Test Equipment / Re: Test Equipment Anonymous (TEA) group therapy thread
« Last post by med6753 on Today at 06:21:14 pm »
You're all a bunch of dirty old men!  :palm: :scared:

Welcome to the club!  >:D >:D :-DD
93
Yes. And it's in Chinese law. If an IP product doesn't have a sales outlet in China, then it's fair game.

Shit, or get off the pot.
More like "Give me your money and I won't rob you. Maybe I'll still rob you."

It's funny that this attitude is probably one of the reasons technology is withheld from China.
94
So China's stance is basically "give us your technology or we'll steal your technology"? With the distinct possibility the technology will still be copied and stolen?

Yes. And it's in Chinese law. If an IP product doesn't have a sales outlet in China, then it's fair game.

Shit, or get off the pot.
95
Projects, Designs, and Technical Stuff / Re: Linear lab power supply
« Last post by xavier60 on Today at 06:16:35 pm »
The power transistor is mounted in direct contact with the heat sink bracket to reduce thermal resistance.
Although this power supply circuit responds to output short circuits much faster than most others, the LM358 takes 20us to take control of output current which peaks to 20 amps.  The TLC072 responds in 2us.
The 3 BD137 transistors from left to right are 8V series pass, Darlington 1st transistor and constant current  load.
Ill post an updated schematic after I do more testing. At this stage I have made only minor changes.
96
ok thanks a lot ;)
97
Beginners / Re: DC2132A Power Supply problems
« Last post by perieanuo on Today at 06:14:52 pm »

[edited]
hi,
I don't get how you implemented dcdc with LTC3632(in his datasheet you input voltage to Vin pin, referenced to Gnd pin 8 and you 'take out' voltage after inductor connected on SW pin, also referenced to pin 8 ).
In your shhematic you apply between Vin and some floating virtual GND and you output between that virtual gnd and the load GND.you made an -5V for some purpose?
I don't see inductive load protection, Q1 may be the first to hit the bucket :)
Let's come to the point, purpose of D5 is doing what?
The tell us what voltage you have on LT3081/SET and Vout, when R31 is 0 with Ilim at max or disconnected and no load. 
regards
98
1. I agree. My guess the end of the trade war is China will give up stealing western IPs tp certain degree, under a condition that the West promises never to sanction China by limiting high tech export to China. From Chinese government's perspective, the West uses high tech sanction to protest dictatorship and Taiwan problem. If China is given a green unconditionally on high tech, China will have no excuse to fund cloning of Western technology.

2. BS. If you can't compete, you deserve to die. China will deal with pollution and many other social problems, but human competing and phasing out human will never change. That's the thrust of natural selection.

3. Politicians know what is good for the human as a race, not the humanity BS. If evolution requires, everyone not up to the standard should and can die.
So China's stance is basically "give us your technology or we'll steal your technology"? With the distinct possibility the technology will still be copied and stolen?
99
Beginners / Re: Question about preamp for measuring noise.
« Last post by Kurski on Today at 06:12:52 pm »
I really had some desperate need for that kind of circuit. I would like to bring some headphone amp breadboarding data on the big screen through Owon 1022i oscilloscope. Now the limit is 40-50mv. I would like to work with signals under typical audio interface noisefloor. Lets say - 120-130db. Accidentally just yesterday I got those chips from mouser.
100
Beginners / Re: TL431 linear power supply
« Last post by spec on Today at 06:11:32 pm »
Hi mike-mike,

Attached below, is a schematic for your PSU as promised. Apologies for the delay, but it took longer to sort than expected, and other things got in the way too. >:(

Bear in mind that this is a paper design and I do not have a full specification for your mains transformer so I have made some assumptions. Also, right now, I do not have access to a lab so I cannot build and test a prototype for you. But I have analyzed the circuit and used a conservative approach whenever possible.

You may find the circuit odd, but it is not an outline circuit like you normally see, and shows the required wiring including star points (SPs), padding, and decoupling.

The two opamp options shown on the schematic are unique, and not any old opamp will do, although you could use other opamps with reduced performance. The OPA192 is the better of the two, but costs a bit more. But, in terms of your PSU there would be little difference in the performance. Mainly the accuracy of the 25V setting would be affected.

The frequency compensation is very heavy, but that is intentional. If necessary the frequency compensation can be optimized at a later date, by a few simple component changes. The important thing is to get the basic circuit working at this initial stage.

You will need very good heat-sinking for the output transistors and fan cooling would be advisable, but we can talk you through all that.

Finally, I cant emphasis how important it is to do a good layout with the connections as shown in the attached schematic. The thick lines on the schematic indicate where thick wires/PCB traces are required. It is also essential to keep wires and PCB traces short and compact. The 100nF capacitor across the supply pins of the opamp, must have short leads and be physically connected to the opamp pins, or as close as possible to the pins. Likewise the padding resistors and other decoupling capacitors must be directly on, or close to the opamp pins.

There is a physical layout that I would recommend, which will simplify construction a lot and optimize performance. Once you have had a look at the schematic, we can discuss the layout if you like.

Unless otherwise stated, all solid capacitors are ceramic X7R through hole types, the physically bigger the better (not surface mount).

The specification for the PSU is 0V to 25V (exactly), 0A to 5A output current.
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