Transcript
[Attached Data] 1. Technica l Da ta No . 002 2. Technica l Da ta No . 039
Service Life o f Capacitors Self- healing (Clearing)
[Reference s] Isamu Ono da: “Manua l for Best u se o f Capa citors” issu ed in 1 975 by Pub lish i ng Departmen t, Tok yo Electrical En gineering College Masuda, e t., a l .: “How to Cho ose and Use D evices /Par ts” issued in 1993 b y Nikkagiren Publishing Company “ Electron ic Device D ata Book 8 5: Circuit Parts” issue d in 19 85 b y NEC “ EIAJ RC R-2350B: Guidelines for Precau tions on Us e o f Plastic Film Capa citors to Be Fixed to Electronic D evices and Eq uipment” published in 200 2 b y Electr onic Indus tries Association of Japan [O ther Boo ks for Re fe rence] The bo oks issued b y CQ Pub lish ing Co mpany, ・ “Characteristics a nd Actual Perfo rmance of Electro n ic Parts to Be Learn t from Wavefor ms” ・ “Handbook for Bes t U se o f Elec tronic Circuit Parts” ・ “Proper Use o f Resistors & Capa citors Suited for Purposes” Attached D ata (1)
e tc . as enumera te d be low: ・ “Good Gro unding in Best Use o f Elec tronic Parts for Beginners” ・ ”Perfec t Pictoria l Bo o k of the Electronic Circuit Parts for Begin ners” ・ “Know-hows to Choos e and Mak e Best Use of Pas sive Parts”
Append ix 1 Service li fe o f capaci tors 1. App lied voltage an d service life For the relatio n b etw een the ap plied volta ge and ser vice life of film capacitors, the Formula 1- 1 is taken up as a sta ndard for the time b eing becaus e it is gene rally easy and simple to h andle and no o ther su itab le re la tion formu la s are ava ilable , thou g h there is a s ligh t s ha d ow o f d oub t w heth er it ma y be t otall y accepted, jud ging from the fact tha t it is based on flimsy theor etica l grou nds. L=LoX(Vo /V) n ･･････････ 1-1 L Lo Vo V n
: : : : :
Service life when oper atin g vo lta ge V, VDC is app lied Service life when oper atin g vo lta ge Vo, VDC is applie d Rated voltage of capacitor Actua l ope rating vo lta ge o f capacitor Constant
(Hr) (Hr) (VDC) (VDC) (4~7)
2. Opera tin g amb ien t temperature and servic e life The temper ature-depe ndence o f film capacitor' s servic e life fo llo ws the Arrh enius L aw, so-called the 10℃ La w. Name ly, if the te mperature rises b y 10℃ , the s e r vice l i fe w il l b e reduced do wn to 1 /2 . There fore , th e re la tion be twee n the amb i ent temper ature and service life is given b y th e Formula 2-1. Tmax - Ta 10
L=LoX2 L Lo Tmax Ta
: : : :
･･･････････ 2-1
Ser v ice li fe at actua l u s e Service life a t ma ximu m opera tin g tempera ture Maximum o perating te mperature Ambient te mperature
(Hr) (Hr) (℃ ) (℃ )
3. Derating o f the ra te d voltage d epending o n the oper atin g temp erature If a capacitor is used at high temperatur es , its ser vice life will be shortened due to therma l de terioration . In case w hen a capa citor is to b e used a t h igh te mper atures , derate the operating voltage in a ccordance with the gr aphs as given below.
4. Ripp le c urrent and service life In case wh en rip ple c urrent is a pplied on a capacitor, Joule h eat will be gen erated . Th e capacitor temperature rise on this occasion is g ive n b y the Formu la 4-1 . △ T= △T Β S C
1 β ･S : : : :
X
I 2 rms ･tan δ ωC
4-1
Surface te mperature rise o f capacitor Radiation c oefficient Surface ar ea o f capacitor Elec trosta ti c capacity of capacitor
(℃ ) (W/℃ ･c ㎡ ) (c ㎡ ) (µF)
Since sign ifican t self- heating of capacitor may le ad to the de ter ioration an d/or damag e to the capacitor, se lf temperature rise o f capa citor should be limite d to lower than 10 ℃ for polyester fi lm capaci to rs and to lo wer th an 5 ℃ for po lypropylene film capacitors. In case o f use a t high tempera tu re/hig h fre quency, th e voltage d eratin g fac tor is differ ent from tha t o f DC voltag e. This is partly b ecause hea ting b y ripp le curren t is severer in conditions than the Ar rhenius 1 0 ℃ Law an d partly be cause in th e po lyes ter film capacitors, etc., tan δ ma y chan ge with the tempera tu re, th us lea ding to the change in self temper ature rise accordingly. 5. Allowab l e voltage in various voltage wa veforms The a llowa ble vo ltag e o f var ious voltage wa ve forms va ries with th e kinds o f wave forms and the fre quency. T he a llowab l e voltage in various voltage wa veforms sha ll be the valu e o bta ined b y mu ltip lying the sine wa ve allowab le voltage a t e ach freque ncy by an y of the coe fficients as give n b elo w. Moreo ver, in case o f th e vo ltage conta i ning th e D C bias comp o nent, the AC vo lta ge o btained b y subtracting the bias voltage from the DC rated volta ge shall be the allowa ble va lue . Then , this voltage sh ould be der ated for use depending on the resp ective freq uencies an d wa veforms. (In case w hen the voltage va lue s on th e vo ltage dera ting cur ves for various kinds o f products in Technical Data No . 0 02 are give n b y effec tive values , the value o btained b y inc r easing the al low a ble vo ltag e value b y 2 √ 2 shall b e the Ep-p valu e. Th en, the va lue obtaine d b y multiplyin g it b y an y of the coe fficients as give n b elo w shall be the allowa ble voltage value Ep-p at the freque ncy of the r elevant wa ve form.) Kind Wavefor m Coefficien t
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Append ix 2 Self-hea lin g (Clear ing ) Since an electrode is evapora ted as a ver y thin meta l film ( abou t 1 50 to 400 Å ) on the dielec tric , even if dielectric brea kdown is caused on the weakest por tion in the die lec tric, only the w eakest portion and its peripheral porti o n w ill be dispers ed instanta neously b y energy o f 1 /2CE2 or I2R and the functions as a capacitor will not be s till los t. This phenomen on is calle d the self-h ealing . The h igher the evapor atio n res istance is an d the thinn er the evap orated film is, the be tter the self-he aling prope rty is. Ho wever, this ma y lead to the poor connection with metallicon and increa se in ESR in the high frequency z one. Ther efore , fu ll inves tigations should be made o n the applications up on its design.
Vacuum evaporation r esistance a nd Self-he aling sta te (AL)
2Ω
6Ω
4Ω
