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参数资料
| 型号： | LM1851MWC |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 电源管理 |
| 英文描述： | 1-CHANNEL POWER SUPPLY SUPPORT CKT, UUC |
| 封装： | WAFER |
| 文件页数： | 6/10页 |
| 文件大小： | 202K |
| 代理商： | LM1851MWC |
Application Circuits
A typical ground fault interrupter circuit is shown in
Figure 2
It is designed to operate on 120 VAC line voltage with 5 mA
normal fault sensitivity
A full-wave rectifier bridge and a 15k2W resistor are used
to supply the DC power required by the IC A 1 mF capacitor
at pin 8 used to filter the ripple of the supply voltage and is
also connected across the SCR to allow firing of the SCR on
either half-cycle When a fault causes the SCR to trigger
the circuit breaker is energized and line voltage is removed
from the load At this time no fault current flows and the IC
discharge current increases from ITH to 3ITH (see Circuit
Description and Block Diagram) This quickly resets both
the timing capacitor and the output latch At this time the
circuit breaker can be reset and the line voltage again sup-
plied to the load assuming the fault has been removed A
10001 sense transformer is used to detect the normal fault
The fault current which is basically the difference current
between the hot and neutral lines is stepped down by 1000
and fed into the input pins of the operational amplifier
through a 10 mF capacitor The 00033 mF capacitor be-
tween pin 2 and pin 3 and the 200 pF between pins 3 and 4
are added to obtain better noise immunity The normal fault
sensitivity is determined by the timing capacitor discharging
current ITH ITH can be calculated by
ITHe
7V
RSET
d
2
(1)
At the decision point the average fault current just equals
the threshold current ITH
ITHe
If(rms)
2
c
091
(2)
where If(rms) is the rms input fault current to the operational
amp and the factor of 2 is due to the fact that If charges the
timing capacitor only during one half-cycle while ITH dis-
charges the capacitor continuously The factor 091 con-
verts the rms value to an average value Combining equa-
tions (1) and (2) we have
RSETe
7V
If(rms)c091
(3)
For example to obtain 5 mA(rms) sensitivity for the circuit in
Figure 2 we have
RSETe
7V
5mAc091
1000
e
15M X
(4)
The correct value for RSET can also be determined from the
characteristic curve that plots equation (3) Note that this is
an approximate calculation the exact value of RSET de-
pends on the specific sense transformer used and LM1851
tolerances Inasmuch as UL943 specifies a sensitivity ‘‘win-
dow’’ of 4 mA – 6 mA provision should be made to adjust
RSET on a per-product basis
Independent of setting sensitivity the desired integration
time can be obtained through proper selection of the timing
capacitor Ct Due to the large number of variables involved
proper selection of Ct is best done empirically The following
design example then should only be used as a guideline
Assume the goal is to meet UL943 timing requirements
Also assume that worst case timing occurs during GF1
start-up (S1 closure) with both a heavy normal fault and a
2X grounded neutral fault present This situation is shown dia-
gramatically below
TLH5177 – 5
UL943 specifies s25 ms average trip time under these con-
ditions Calculation of Ct based upon charging currents due
to normal fault only is as follows
s
25 ms Specification
b
3 ms GFI turn-on time (15k and 1 mF)
b
8 ms Potential loss of one half-cycle due to fault current
sense of half-cycles only
b
4 ms Time required to open a sluggish circuit breaker
s
10 ms Maximum integration time that could be allowed
8 ms Value of integration time that accommodates com-
ponent tolerances and other variables
Ct e
I c T
V
(5)
where T e integration time
V e threshold voltage
I e average fault current into Ct
I e
120VAC(rms)
RB
J c RN
RG a RN
J
X
YX
Y
heavy fault
portion of
current generated
fault current
(swamps ITH)
shunted
around GFI
c
1turn
1000 turns
J c 12J c (091)
(6)
X
YX YX Y
current
Ct charging
rms to
division of
on half-
average
input sense
cycles only
conversion
transformer
therefore
Cte
120
500
J c 04
16a04
J c 11000J c 12Jc(091)( c00008
175
(7)
Cte 001 mF
5
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LM1851MX | 功能描述:电流和电力监控器、调节器 RoHS:否 制造商:STMicroelectronics 产品:Current Regulators 电源电压-最大:48 V 电源电压-最小:5.5 V 工作温度范围:- 40 C to + 150 C 安装风格:SMD/SMT 封装 / 箱体:HPSO-8 封装:Reel |
| LM1851MX/NOPB | 功能描述:电流和电力监控器、调节器 RoHS:否 制造商:STMicroelectronics 产品:Current Regulators 电源电压-最大:48 V 电源电压-最小:5.5 V 工作温度范围:- 40 C to + 150 C 安装风格:SMD/SMT 封装 / 箱体:HPSO-8 封装:Reel |
| LM1851N | 功能描述:电流和电力监控器、调节器 RoHS:否 制造商:STMicroelectronics 产品:Current Regulators 电源电压-最大:48 V 电源电压-最小:5.5 V 工作温度范围:- 40 C to + 150 C 安装风格:SMD/SMT 封装 / 箱体:HPSO-8 封装:Reel |
| LM1851N/A+ | 制造商:未知厂家 制造商全称:未知厂家 功能描述:Ground Fault Interrupter |
| LM1851N/B+ | 制造商:未知厂家 制造商全称:未知厂家 功能描述:Ground Fault Interrupter |
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