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Old 12th April 2013, 02:55 PM   #81
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Default Transistor Tester Capacitor ESR Inductance Resistor Meter

Quote:
Originally Posted by necplusultra View Post
@enjoybiking,
I'm interested in a few chips. I don't think you need custom forms filled to ship here.

Question: how do you grade and measure those fets? I have a few on hand and would like to know how to measure measure them.

thanks and regards
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Transistor Tester Capacitor ESR Inductance Resistor Meter


usually under $20 USD you want the one with the square LSI not rectangular [on the bottom board]. Note the SOT23 pads lower left. Drop the FET on the pads, then hold down hard with tweezers, hit button and wait. Tester will hold the reading a while then shut down.


If you only have a few FETs your luck may not be good trying to get matched quads of each type. You would need quite a few, I am glad I started with 100 each type -- I already acquired 200 more.


Customs form is required for Canada...I can do it for YOU, but I still have a USA beta tester fellow to make happy first. I have most of what is needed.
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Old 12th April 2013, 03:12 PM   #82
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Default OOOpz

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Originally Posted by qusp View Post
how are you matching them? single point IDSS, curve trace, transconductance at operating point, multipoint IDSS etc ? single point IDSS is not terribly useful really. not to diminish your efforts, but selling properly matched fets is not a value proposition for the seller and the still rather significant effort required to test in a simple way is not really that much better than picking quads from next to each other on a strip when it comes to dynamic performance, especially if it is not even a single point that is the same as the operating point in the design they will be used in.
No curve trace here. See my other posting about the tester. It does a Vgs and Idss for each device. Without this basic test people would be WAY WAY off grabbing 8 random FETs. DO I want to grade and match for the world? NO.
I AM trying to make sure folks understand how wildly different the readings are on a strip of FETs from the same reel -- this is DIY but ignoring the matching altogether would not be good. On one grid for example, 2.07 vs 3.47 Vgs miles apart. When faced with THAT, I'd want at least close basic readings, no? A DIY trying to order a small QTy on their own is going to be, I think, unlucky. EVen at the basic level.
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Old 12th April 2013, 03:39 PM   #83
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thanks.

I'll certainly purchase for my personal use. What do you mean by "square LSI not rectangular" where can I see that on the ebay listings?

Also, I'll send you a pm for chips and boards.

regards.


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Old 12th April 2013, 03:47 PM   #84
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Quote:
Originally Posted by curryman View Post
I myself have three boards up and running and I am about to put them into my miniSHARC based DSP system.

V2 is almost finished and a first batch will probably be ordered this weekend.

Stay tuned...
Hi curryman, I'm pcpete from the minidsp forums....I've been following your progress here and on the minidsp forums..

I'm the guy who bought 3 ebay es9023 i2s dacs......I've got 2 of them working with the sharc by simply just splitting the clock signals...once I add the 3rd dac..the music stutters and then just dies....

Just wondering how you are making out connecting your 3 dacs to the minisharc....I'll probably switch to your design eventually...thx
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Old 12th April 2013, 03:50 PM   #85
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Quote:
Originally Posted by enjoybiking View Post
No curve trace here. See my other posting about the tester. It does a Vgs and Idss for each device. Without this basic test people would be WAY WAY off grabbing 8 random FETs. DO I want to grade and match for the world? NO.
I AM trying to make sure folks understand how wildly different the readings are on a strip of FETs from the same reel -- this is DIY but ignoring the matching altogether would not be good. On one grid for example, 2.07 vs 3.47 Vgs miles apart. When faced with THAT, I'd want at least close basic readings, no? A DIY trying to order a small QTy on their own is going to be, I think, unlucky. EVen at the basic level.
so its single point and not at operating conditions, so not that much better that taking devices from right next to each other on the strip no, if the reading is taken for a different time, different temperature and in different operating conditions, its really not very useful.

you could test the very same device for a different amount of time, at a different current and voltage and different temperature and get a significantly different IDSS and VGS reading.

like many people who buy devices to match them in an endeavor that is supposed to make money, or simply for other hobbiests, it seems you didnt know what you were getting into. dont worry many before you have done the same, including myself, but for 200 boards, thats crazy

$20? you could build the same thing for $3-4 with a 9v battery, a resistor and a switch.

hey the listings say they test for mosfet VGth not VGS, but perhaps the standard VGS measurement is part of other options mot mentioned? gate threshold is more important for switching applications. you may be able to make a somewhat useful instrument out of it with a few mods though.

I would stick with Erno's method over this. i'll link in a minute, more work though, so maybe you dont want to know

Last edited by qusp; 12th April 2013 at 04:18 PM.
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Old 12th April 2013, 03:56 PM   #86
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these 9023 boards may not be as bad, as the i2s is buffered with flip flops, but the trace and cable capacitance for so many dacs in parallel may still cause issues
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Old 12th April 2013, 04:13 PM   #87
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Default The cheap tester

Quote:
Originally Posted by necplusultra View Post
thanks.

I'll certainly purchase for my personal use. What do you mean by "square LSI not rectangular" where can I see that on the ebay listings?

Also, I'll send you a pm for chips and boards.

regards.


The older model if the tester has a long rectangular LSI on the base board [some vendors have great pictures], the newer model has square LSI. Latest one I have seen also has V2.2 showing on the lower PCB artwork lower center front of base-PCB. So *if* you invest in one, get that or newer, or if you can afford better, great. It tests lots of components at a basic level, I am happy to have one.
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Old 12th April 2013, 05:11 PM   #88
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handy yes, absolutely for a quick basic level test, but its accuracy will be generally worse than a fairly entry level multimeter (which most of us already have) that can do all the same things and much more, with a few added passive components.

but for reasonably accurate VGS testing for specific circuits, not so much.

this will produce better results


with the current sources adjusted to reflect your operating conditions. the noise of the current sources is not so important for the tester, so you could even use an LT3092 or IXYS adjustable current source

Last edited by qusp; 12th April 2013 at 05:25 PM.
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Old 13th April 2013, 01:24 PM   #89
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Quote:
Originally Posted by pcpete View Post
Hi curryman, I'm pcpete from the minidsp forums....I've been following your progress here and on the minidsp forums..

I'm the guy who bought 3 ebay es9023 i2s dacs......I've got 2 of them working with the sharc by simply just splitting the clock signals...once I add the 3rd dac..the music stutters and then just dies....

Just wondering how you are making out connecting your 3 dacs to the minisharc....I'll probably switch to your design eventually...thx
I did not have the time yet to do my own tests but after looking into the datasheets of the DSP the I2S data outputs probably have not enough drive capability to drive more than two or three receiver. Also reflections from not properly designed traces might be a problem (traces and connections on my board have 50Ohm impedance).
With my boards using its own MCLK we will not have any problem with MCLK and SDI (each data output is only connected to one board), but LRCLK and BCLK must be shared and thats a problem. I am just working on an active solution using buffers (either 74HC244 or CDCVLVC1104 Fanout Buffer) however that may take some time. I will also discuss this with DevTeam from miniDSP.

@qusp: You are of course perfectly right how to do proper matching. However I did several tests with different matching procedures and for the JG buffer we are talking about here the matching with those little tester will be perfectly OK. Output DC is close to zero and distortion is sufficiently low.
A better matching might reduce both further but if you really want to improve the whole thing you'd better think about changing the buffer design (e.g. preamp buffers). At the end you might end up with a better design but probably loose the appealing simplicity
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Old 13th April 2013, 03:55 PM   #90
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Finally finished stuffing the board this morning. I'll come back to it this weekend and power it up.
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