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|  DSH 384$ d4 \4 _7 r1 [+ A
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| Lithium Cell Protection! \3 i: ^0 z/ P; t2 W# {3 J5 F
| 4.3.21
& P8 J7 C3 y3 Y$ _5 t1 N | 60950(ed.2)
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Standard: IEC60950, 2nd Clause: 4.3.21 Sheet n. P384
u# a2 \$ h* u8 U( o: Q& o( @Page 1(1): }$ W, p7 W$ N, V
Subject: Lithium Cell Protection Key words:, i! Q% |. o$ L- q1 A" I6 x4 q
-Lithium Cell
, c2 `7 ]. k& @2 x; e-Clearances
. E/ \( q7 \6 Q V' V5 t- failure mode
# t" v5 K, f3 Z. LProvisional Decision taken by ETF2/ C7 }4 ^- E- c% w
and to be approved by CTL at its
# _0 G7 c3 n% I6 }# l38th meeting, in Toronto
- @3 u: ^; i4 |# U, N/ J" rQuestion:
: J# s0 \9 g% P: B8 x7 @- x5 wClause 4.3.21 requires that two levels of protection are required to prevent forced or reversed charge# e8 K, D+ Q1 S" n2 @+ W
or forced discharge if this would result in a hazard. Conventionally a combination of resistor, diode
0 X8 k ~5 o( r1 Y. W; g* jor ic has been considered suitable and is for the series current path. However, a new consideration
( ?5 P4 u3 E; c; m6 I& Lhas been raised in respect of adjacent tracks, separated by no more than operational insulation, which,5 C; }. r' B+ O! K) |* D8 o
under s/c conditions will bypass the protective series components and provide charging current for% K0 T' e8 f. m; c' ~- E; y
either chargeable or non-rechargeable batteries. Does this mean that there is therefore a requirement8 _- T$ Y7 \" ^5 k H
for Reinforced separation?, v, l) G; ^. O0 u3 T3 s! Y
If that is the case, then the controlling factor is the clearance of 0.8mm in Table 5 (circuits not subject4 n$ b4 w. U7 r x* D( |8 g! X# q
to transient over voltage). This is based on the fact that creepage cannot be less than clearance and8 E, I" b* Y3 n' D8 |% C
creepage can be calculated to be, for example at +5V, 0.4mm (based on rounding up 0.12mm to
, p7 C3 {; s! ?6 G" I0.2mm for Basic and doubling for reinforced.
/ `: q+ c, [; kDecision:: \- T4 }$ |6 ?- v; k
Operational insulation is suitable taking into account 5.4.4 because there is no risk of electric shock.2 Y4 h2 E/ ^ b- c4 L2 ]3 C
(see 1.2.9.1)0 k$ J+ v- [. |! [3 ]
Care should be taken by determining clearance and creepage distances which column of the table has7 a6 U- n$ ?5 ]( [/ z" Y
to be used.(Transients have to be taken into account)2 y6 v1 j5 s1 P6 N, V A
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