{"id":287,"date":"2015-12-02T13:56:43","date_gmt":"2015-12-02T12:56:43","guid":{"rendered":"http:\/\/ok2haz.ok2kld.cz\/ok2haz\/?p=287"},"modified":"2021-11-06T11:19:27","modified_gmt":"2021-11-06T10:19:27","slug":"laboratorni-zdroj-volba-soucastek","status":"publish","type":"post","link":"https:\/\/ok2haz.ok2kld.cz\/ok2haz\/2015\/12\/laboratorni-zdroj-volba-soucastek\/","title":{"rendered":"Laboratorn\u00ed zdroj – 3. volba sou\u010d\u00e1stek"},"content":{"rendered":"

Tento \u010dl\u00e1nek navazuje na popis laboratorn\u00edho zdroje,<\/a> kter\u00fd stav\u00edme s Frantou OK2JNJ.<\/p>\n

Volba sou\u010d\u00e1stek je jedn\u00edm z nejd\u016fle\u017eit\u011bj\u0161\u00edch krok\u016f. Sna\u017eil jsem se p\u0159i v\u00fdb\u011bru pou\u017e\u00edvat sou\u010d\u00e1stky co nejkvalitn\u011bj\u0161\u00ed a z\u00e1rove\u0148 nejdostupn\u011bj\u0161\u00ed, cena byla faktor podru\u017en\u00fd.<\/p>\n

Rezistory<\/h3>\n

Pokud sv\u016fj z\u00e1jem soust\u0159ed\u00edme na teplotn\u00ed drift rezistor\u016f, pak zjist\u00edme, \u017ee uhl\u00edkov\u00e9 rezistory maj\u00ed drift cca 300 a\u017e 1000 ppm\/K, dr\u00e1tov\u00e9 cca 300 ppm\/K a metalizovan\u00e9 50 ppm\/K.<\/p>\n

1 % = 10 000 ppm (Parts Per Milion) je v\u00fdraz pro jednu miliontinu celku<\/strong><\/p>\n

SMD metalizovan\u00e9 odpory maj\u00ed napa\u0159enou vodivou vrstvi\u010dku na keramick\u00e9m nosn\u00e9m podkladu.Vrstvi\u010dka se nan\u00e1\u0161\u00ed na keramick\u00e9 nosi\u010de rozpra\u0161ov\u00e1n\u00edm<\/span> (<\/span>vakuov\u00e1<\/span> depozice<\/span>), vodiv\u00fd materi\u00e1l<\/span> se napa\u0159\u00ed na<\/span> izola\u010dn\u00ed<\/span> podklad<\/span>. Vzhledem k tomu, \u017ee<\/span> doba <\/span>po kterou se prov\u00e1d\u00ed<\/span> rozpra\u0161ov\u00e1n\u00ed<\/span> m\u016f\u017ee b\u00fdt \u0159\u00edzena,<\/span> tlou\u0161\u0165ka<\/span> tenk\u00e9ho filmu<\/span> pak odpov\u00edd\u00e1 expozi\u010dn\u00ed dob\u011b.Typ materi\u00e1lu se tak\u00e9 obvykle<\/span> li\u0161\u00ed<\/span>, skl\u00e1d\u00e1 se z<\/span> jednoho nebo v\u00edce<\/span> keramick\u00fdch<\/span> (<\/span>cermetov\u00fdch) vodi\u010d\u016f<\/span>, jako je nitrid<\/span> tantalu<\/span> (<\/span>TaN), oxid<\/span> ruthenia<\/span> (<\/span>RuO2<\/span>), oxid<\/span> olovnat\u00fd<\/span> (<\/span>PbO),Bi2RU<\/span>2O<\/span>7<\/span>, nikl<\/span> chrom<\/span> (<\/span>NiCr), nebo<\/span> (<\/span>Bi2Ir<\/span>2O<\/span>7<\/span>).<\/span><\/p>\n

Odpor nen\u00ed od v\u00fdroby p\u0159esn\u00fd, <\/span>obvykle jsou <\/span>na spr\u00e1vnou<\/span> hodnotu<\/span> ubru\u0161ov\u00e1ny nebo o\u0159ez\u00e1v\u00e1ny laserem na toleranci 0,1<\/span>\/<\/span> 0,2 \/<\/span> 0,5<\/span>, nebo 1<\/span>%, a<\/span> s<\/span> teplotn\u00edmi koeficienty<\/span> 5-25<\/span> ppm<\/span>\/K<\/span>.<\/p>\n

Volba rezistor\u016f tedy byla: SMD metalizovan\u00e9<\/p>\n

Proudov\u00fd bo\u010dn\u00edk<\/h3>\n

Zva\u017eovali jsme, zda pou\u017e\u00edt pro m\u011b\u0159en\u00ed proudu senzor s hallov\u00fdm \u010didlem, ten v\u0161ak nen\u00ed line\u00e1rn\u00ed. Dal\u0161\u00ed mo\u017enost\u00ed je dr\u00e1tov\u00fd odpor, ten m\u00e1 zase p\u0159\u00edli\u0161 velk\u00fd vlastn\u00ed \u0161um a teplotn\u00ed nestabilitu. Nakonec jsem vybral Shunt rezistor<\/a> „open air“ s hodnotou 20m\u03a9(10m\u03a9) \/ 3W.
\nTen sv\u00fdmi parametry vych\u00e1zel nejl\u00e9pe:
\nTeplotn\u00ed drift – 20ppm\/\u00baC
\nParazitn\u00ed induk\u010dnost < 10nH
\nOteplen\u00ed p\u0159i 3W (12\/24A)
\n– t\u011blo bo\u010dn\u00edku 160\u00b0C
\n– v bod\u011b p\u00e1jen\u00ed 70\u00b0C<\/p>\n

Opera\u010dn\u00ed zesilova\u010de<\/h3>\n

Opera\u010dn\u00ed zesilova\u010de jsou op\u011bt kapitola sama pro sebe. Do desky jdou bez probl\u00e9m\u016f osadit oby\u010dejn\u00e9 OP27 (40k\u010d), j\u00e1 volil kv\u016fli parametr\u016fm Texas Instruments OPA228 (100k\u010d) serie BurrBrown. OPA228 vlastnosti m\u00e1 velmi n\u00edzk\u00fd vlastn\u00ed \u0161um (3nV\/Hz), je \u0161irokop\u00e1smov\u00fd 33MHz s rychlost\u00ed p\u0159eb\u011bhu 10V\/us (OP27 2,8V\/us ). Usazovac\u00ed \u010das je 5us co\u017e ze oproti OP27 velk\u00fd rozd\u00edl. Nav\u00edc OPA228<\/strong> je n\u00e1hrada a v\u00fdvojov\u00fd n\u00e1stupce OP27\/37. Opera\u010dn\u00ed zesilova\u010de pro p\u0159izp\u016fsoben\u00ed impedance ADC jsou typu LM8261<\/strong>, ty v\u0161ak nemaj\u00ed moc dobr\u00e9 parametry- v\u011bt\u0161\u00ed \u0161um, v\u011bt\u0161\u00ed teplotn\u00ed nestabilitu a ofset nap\u011bt\u00ed. Tak\u017ee je chceme nahradit typem OPA192<\/strong>, kter\u00fd m\u00e1 tyto parametry potla\u010den\u00e9.<\/p>\n

Srovn\u00e1vac\u00ed tabulka opera\u010dn\u00edch zesilova\u010d\u016f<\/h4>\n\n\n\n\n\n\n\n\n\n\n
<\/td>\nOPA228<\/td>\nOP27<\/td>\nLM8261<\/td>\nOPA192<\/td>\nMAA748<\/td>\n<\/tr>\n
Noise<\/td>\n3nV\/\u221aHz<\/td>\n5,5nV\/\u221aHz<\/td>\n15nV\/\u221aHz<\/td>\n5,5nV\/\u221aHz<\/td>\n<\/td>\n<\/tr>\n
Bandwidth<\/td>\n33MHz, 10V\/\u00b5s<\/td>\n8MHz, 2,8V\/\u00b5s<\/td>\n21MHz, 10V\/\u00b5s<\/td>\n10MHz, 20V\/\u00b5s<\/td>\n<\/td>\n<\/tr>\n
Set. Time<\/td>\n5\u00b5s<\/td>\n<\/td>\n0,4\u00b5s<\/td>\n0,9\u00b5s<\/td>\n20\u00b5s<\/td>\n<\/tr>\n
Temp. Stabil.<\/td>\n0,1\u00b5V\/\u00b0C<\/td>\n\n

0,4\u00b5V\/\u00b0C<\/p>\n<\/td>\n

\n

2\u00b5V\/\u00b0C<\/p>\n<\/td>\n

0,15\u00b5V\/\u00b0C<\/td>\n3\u00b5V\/\u00b0C<\/td>\n<\/tr>\n
CMRR<\/td>\n138dB<\/td>\n126dB<\/td>\n100dB<\/td>\n140dB<\/td>\n90dB<\/td>\n<\/tr>\n
Offset voltage<\/td>\n5\u00b5V<\/td>\n25\u00b5V max<\/td>\n700\u00b5V<\/td>\n10\u00b5V<\/td>\n7,5mV<\/td>\n<\/tr>\n
Input BIAS current<\/td>\n10nA max<\/td>\n40nA max<\/td>\n490nA<\/td>\n20pA max<\/td>\n120nA<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Trimry<\/h3>\n

Pro nastaven\u00ed offsetu OZ jsou pou\u017eity trimry VISHAY<\/a> .<\/p>\n

Nap\u011b\u0165ov\u00e1 reference<\/h3>\n

Je TI REF5025 (2,5V)(100k\u010d), extern\u00ed referenci jsem volil kv\u016fli stabilit\u011b, zam\u011bnitelnosti a nutnosti m\u00edt jedno referen\u010dn\u00ed nap\u011bt\u00ed spole\u010dn\u00e9 pro oba p\u0159evodn\u00edky. Nav\u00edc REF5025 m\u00e1 jako jedin\u00e1 z \u0159ady testy pro Military pou\u017eit\u00ed.<\/p>\n

Kl\u00ed\u010dov\u00e9 parametry REF5025:<\/h4>\n