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參數(shù)資料
| 型號(hào)： | LM1851 |
| 廠商： | Fairchild Semiconductor Corporation |
| 英文描述： | Ground Fault Interrupter(電源接地失敗中斷器) |
| 中文描述： | 接地故障遮斷（電源接地失敗中斷器） |
| 文件頁(yè)數(shù)： | 2/12頁(yè) |
| 文件大小： | 87K |
| 代理商： | LM1851 |
LM1851
PRODUCT SPECIFICATION
2
Functional Description
The voltage at the supply pin is clamped to +26V by the
internal shunt regulator D3. This shunt regulator also
generates an artificial ground voltage for the noninverting
input of A1 (shown as a +10V source). A1, Q1, and Q2 act a
a current mirror for fault current signals (which are derived
from an external transformer). When a fault signal is present,
the mirrored current charges the external timing capacitor
until its voltage exceeds the latch trigger threshold (typically
17.5V). When then this threshold is exceeded, the latch
engages and Q3 turns off, allowing I
2
to drive the SCR
connected to pin 1.
Extra Circuitry in the feedback path of A1 works with the
switched current source I
1
to remove any charge on C
T
induced by noise in the transformer. If no fault current is
present, then I
1
discharges C
T
with a current equal to 3 I
TH
,
where I
TH
is the value of current set by the external R
SET
resistor. If fault signals are present at the input of A1 (which
is held at virtual ground, +10V), one of the two current
mirrors in the feedback path of A1 (Q4 and Q5) will become
active, depending on which half-cycle the fault occurs.
This action will raise the voltage at V
S
, switching I
1
to a
value equal to I
TH
, and reducing the discharge rate of C
T
to
better allow fault currents to charge it.
Notice that I
TH
discharges C
T
during both half-cycles of the
line, while I
F
only charges C
T
during the half-cycle in which
I
F
exits pin 2 (since Q1 will only carry fault current in one
direction). Thus, during one half-cycle, I
F
-I
TH
charges C
T
,
while during the other half-cycle I
TH
discharges it.
Pin Assignments
SCR Trigger
– Input
+ Input
Ground
65-1851-02
+V
S
C
T
R
SET
Amp Out
1
2
3
4
8
7
6
5
Definition of Terms
Normal Fault
An unintentional electrical path, R
B
, between the load termi-
nal of the hot line and the ground, as shown by the dashed
lines in Figure1.
Figure 1. Normal Fault
Grounded Neutral Fault
An unintentional electrical path between the load terminal of
the neutral line and the ground, as shown by the dashed lines
in Figure 2.
Figure 2. Grounded Neutral Fault
Hot
GFI
Neutral
Line
Hot
R
LOAD
R
B
Neutral
R
G
65-1851-03
Hot
GFI
Neutral
Line
Hot
R
LOAD
R
IN
Neutral
R
G
65-1851-05
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