LM1851 Unisonic Technologies, LM1851 Datasheet - Page 7

• Manufacturer Part Number: LM1851
• Description: Ground Fault Interrupter
• Manufacturer: Unisonic Technologies

UTC LM1851
APPLICATION CIRCUITS
charging current. The effect of neutral loop induced currents is difficult to quartile, but typically they sum with normal
fault currents, thus allowing a larger value of C1.
better noise immunity obtained. The larger capacitor can be accommodated because R
allowing the full fault current, I, to enter the GFI.
continuously and allowing some of the energy to couple into the sense transformer during conditions of neutral fault.
TYPICAL APPLICATION
UTC
LOAD
In practice, the actual value of C1 will have to be modified to include the effects of the neutral loop upon the net
For UL943 requirements, 0.015μF has been found to be the best compromise between timing and noise.
For those GFI standards not requiring grounded neutral detection, a still larger value capacitor can be used and
In Figure 2, grounded neutral detection is accomplished by feeding the neutral coil with 120 Hz energy
NEUTRAL
HOT
UNISONIC TECHNOLOGIES CO., LTD.
MOV
* Adjust R
FIGURE 2. 120Hz Neutral Transformer Approach
BREAKER
CIRCUIT
SET
0.01/400V
for desired sensitivity
SCR
LINEAR INTEGRATED CIRCUIT
0.01
0.01/400V
15K/2W
GND/NEUTRAL COIL
200:1
HIGH µ COIL
C
0.015
t
+
7
1
5
8
1.0μF
TANT
TIMING
CAP
SCR
TRIGGER
OP AMP
OUTPUT
V
CC
R
SET
*
R
GND
+IN
SET
N
-IN
and R
2
3
6
4
SENSE COIL
G
1000:1
0.0033
200 pF
are not present,
QW-R122-007,A
+
10 μF
TANT
7
LINE