ETC RV4146

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Description
www.fairchildsemi.com
RV4140A
Low Power Two-Wire Ground Fault
Interrupter Controller
Features
Description
•
•
•
•
•
•
•
•
•
•
The RV4140A is a low power controller for AC outlet
appliance leakage circuit interrupters. These devices detect
hazardous current paths to ground such as an appliance
falling into water. The interrupter then open circuits the line
before a harmful or lethal shock occurs.
Powered from the AC line
Built-in bridge rectifier
Direct interface to SCR
350 mA quiescent current
Adjustable trip current
Adjustable time delay
Minimum external components
Meets UL 943 requirements
Specifically for two-wire systems
For use with 110V or 220V systems
Internally, the RV4140A has a diode bridge rectifier, zener
shunt regulator, op amp, current reference, time delay circuit,
latch and SCR driver.
An external sense transformer, SCR, relay, two resistors
and three capacitors complete the design of the circuit
interrupter. The simple layout and minimum component
count ensure ease of application and long term reliability.
Block Diagram
RV4140A
8
1
2
7
Latch
4.7K
Delay
6
3
Vcc
4
5
65-4140A-01
Rev. 1.0.0
RV4140A
PRODUCT SPECIFICATION
Functional Description
Supply Current Requirements
(Refer to Block Diagram and Figure 1 )
The RV4140A has a built-in diode bridge rectifier that
provides power to the chip independent of the polarity of
the AC line. This eliminates the external rectifier required for
previous GFCI controllers.
The shunt regulator generated by a 6.5V zener diode is
built into the internal bridge rectifier. It is divided to create
an internal reference voltage of 2.9V connected to pin 3.
The secondary of the sense transformer is AC coupled to the
inverting input of the sense amplifier at pin 2; the non-inverting input is referenced to pin 3. A current feedback loop
around the sense amplifier ensures a virtual ground will be
presented to the secondary of the sense transformer. In this
manner it acts as a current transformer instead of a voltage
transformer. In this mode, the transformer’s characteristics
are very predictable and circuit adjustments are not necessary in production.
The sense transformer has a toroidal core made of laminated
steel rings or solid ferrite material. The secondary of the
transformer is 500 to 1000 turns of #40 wire wound through
the toroid. The primary’s one turn made by passing the
AC hot and neutral wires through the center of the toroid.
When a ground fault exists, a difference exists between the
current flowing in hot and neutral wires. The difference
primary current, divided by the number of secondary turns,
flows through the secondary wire of the transformer.
The AC coupled transformer secondary current then flows
through the sense amplifier’s feedback loop, creating a full
wave rectified version of the secondary fault current. This
current passes through RSET at pin 1, generating a voltage
equal to RSET times the peak fault current divided by the
sense transformer turns ratio. This voltage is compared with
the reference voltage at pin 3.
RLlNE limits the shunt regulator current to 2 mA. The recommended value is 47K to 91K for 110V systems and 91K
to 150K for 220V systems. The recommended maximum
peak line current through RLlNE is 7 mA.
DO NOT connect a filter capacitor between pins 5 and 6 in
an attempt to filter the supply voltage at the RV4140A.
Proper operaton of the RV4140A requires the internal supply
voltage to be unfiltered.
SCR Driver
The SCR must have a high dV/dt rating to ensure that line
noise (generated by electrically noisy appliances) does not
falsely trigger the SCR. Also, the SCR must have a gate drive
requirement less than 200 mA. C3 is a noise filter that
prevents high frequency line pulses from triggering the SCR.
The relay solenoid used should have a 3 ms or less response
time to meet the UL 943 timing requirement.
Supplier of Sense Transformers and Cores
Magnetic Metals Corporation, Camden, NJ 08101,
(609) 964-7842, supplies a full line of ring cores and transformers designed specifically for GFCI and related applications.
Determining the Values of RSET and C2
If the voltage at pin 1 is greater than pin 3, a comparator will
charge C2 through a 29 mA current source at pin 8. If the
voltage at pin 1 exceeds pin 3 for longer than the delay time,
a 400 mA current will pulse between pins 7 and 6 which will
trigger the gate of the SCR.
If the voltage at pin 1 exceeds pin 3 for less than the delay
time, the SCR will not trigger.
The fault current at which the controller triggers the SCR
is dependent on the value of RSET and the time delay
determined by C2.
UL 943 requires the circuit interrupter trip when the ground
fault exceeds 6 mA and not trip when the fault current is less
than 4 mA.
2
Determine the ground fault trip current requirement. This
will be typically 5 mA in North America (117 VAC) and
10 mA in the UK and Europe.
Determine the minimum amount of time delay required to
prevent nuisance tripping. This will typically be 1 to 2 ms.
The value of C2 required to provide the desired delay time
is:
C2 = 10 x T
where C2 is in nF, and T is the desired delay time in ms.
PRODUCT SPECIFICATION
RV4140A
The value of RSET to meet nominal ground fault tip current
specification is:
This formula assumes an ideal sense transformer is used.
The calculated value of RSET may have to be changed up to
30% when using a non-ideal transformer.
2.05 ´ N
R SET = --------------------------------------------------------------I FAULT ´ COS 180 ( T ¤ P )
Where:
•
•
•
•
RSET is in kW
T is the time delay in ms
P is the period of the line frequency in ms
IFAULT is the desired ground fault trip current in mA
RMS.
• N is the number of sense transformer secondary turns.
RTEST
15K
Mov
Sense Transformer
1:500 Turns Ratio
3 Ring Steel Core
Press to Test
Normally
Latching
Closed
Contacts
Hot
Line
Load
Neutral
C1
10 m F
RSET
191K
1
8
2
3
C4
0.1m F
4
Solinoid
C2
0.02 m F
7
RV4140A
6
Q1
Tag
X0103DA
RLINE
91K
C3
10 nF
5
65-4140A-02
Figure 1. Appliance Leakage Detector Circuit Application
3
RV4140A
PRODUCT SPECIFICATION
Pin Assignments
PDIP
(Top View)
SOIC
(Top View)
RSET 1
8 C Delay
VFB 2
7 SCR Trigger
2.9V 3
6 Neutral
Ground 4
5 Line
RSET
1
8
C Delay
VFB
2
7
SCR Trigger
2.9V
3
6
Neutral
Ground
4
5
Line
65-4140A-03
Absolute Maximum Ratings
Parameter
Min.
Supply Current
Internal Power Dissipation
Typ.
Max.
Units
7
mA
500
mW
Storage Temperature Range
-65
+150
°C
Operating Temperature Range
-35
+80
°C
60 Seconds, DIP
+300
°C
10 Seconds, SOIC
+260
°C
Lead Soldering Temperature
Thermal Characteristics
Parameter
4
8 Lead Plastic SOIC
8 Lead Plastic DIP
Maximum Junction Temperature
+125°C
+125°C
Maximum PDTA<50°C
300 mW
468 mW
Thermal Resistance, qJA
240°C/W
160°C/W
For TA > 50°C Derate at
4.1 mW/°C
6.25 mW/°C
PRODUCT SPECIFICATION
RV4140A
Electrical Characteristics
ILINE = 1.2mA and TA = +25°C, RSET = 290kW
Parameters
Test Conditions
Min.
Typ.
Max.
Units
Shunt Regulator (Pins 5 to 4)
Regulated Voltage
I2-3 = 11mA
6.8
7.2
7.6
V
Regulated Voltage
ILINE = 700 mA, I2-3 = 9mA
6.8
7.2
7.6
V
Offset Voltage
Design Value
-3.0
0
3.0
mV
Gain Bandwidth
Design Value
2.0
Input Bias Current
Design Value
30
100
nA
4.0
4.7
5.4
kW
Sense Amplifier (Pins 2 to 3)
MHz
SCR Trigger (Pins 7 to 6)
Output Resistance
V5-6 = open, I2-3 = 0mA
Output Voltage
I2-3 = 9mA
0
0.1
10
mV
Output Voltage
I2-3 = 11mA
1.4
2.0
2.6
V
Output Current
V7-6 = 0V, I2-3 = 11mA
300
420
600
mA
ILINE = 700 mA
2.6
2.9
3.2
V
Delay Time1
C8-4 = 20nF
—
2.0
—
ms
Delay Current
I2-3 = 11mA
23
29
35
mA
Reference Voltage (Pins 3 to 4)
Reference Voltage
Delay Timer (Pins 8 to 4)
Note:
1. Delay time is defined as starting when the instantaneous sense current (I 2-3) exceeds 2.9V/RSET and ending when the SCR
trigger voltage V7-6 goes high.
5
6
(2)
(3)
Common
V FB
Ground
(4)
Q2
Q6
R1
10K
Q3
Q12
R4
50K
Q7
VCC
Q5
R3
8.5K
Q8
Q44
C1
Q16
Q11
(1)
R SET
R6
2.5K
Q15
Q10
6.5 pF
Q9
R2
10K
R5
50K
Q13 Q14
R8
23K
Q19
Q17
R7
23K
Q20
Q18
Q23
Q21
Sub
Q24
Q25
Q22
Q28
Q26
Q27
Q32
Q29Q30
Sub
Q33
Q31
Q38
Sub
Sub
Q35
Q34
Q36
Q40
R9
83K
Q37
Q39
Q42
Q41
Q43
Q44
Q46
Q45
Q49
Q47
R10
4.7K
Q50
Q48
65-4653
Cap
(8)
SCR
(7)
Neutral
(6)
Line
(5)
RV4140A
PRODUCT SPECIFICATION
Schematic Diagram
PRODUCT SPECIFICATION
RV4140A
Notes:
7
RV4140A
Notes:
8
PRODUCT SPECIFICATION
PRODUCT SPECIFICATION
RV4140A
Notes:
9
RV4140A
PRODUCT SPECIFICATION
Mechanical Dimensions
8-Lead Plastic DIP Package
Inches
Symbol
A
A1
A2
B
B1
C
D
D1
E
E1
e
eB
L
Millimeters
Min.
Max.
Min.
Max.
—
.015
.115
.014
.045
.008
.348
.005
.300
.240
.210
—
.195
.022
.070
.015
.430
—
.325
.280
—
.38
2.93
.36
1.14
.20
8.84
.13
7.62
6.10
5.33
—
4.95
.56
1.78
.38
10.92
—
8.26
7.11
.100 BSC
—
.430
.115
.160
2.54 BSC
—
10.92
2.92
4.06
8¡
8¡
N
Notes:
Notes
1. Dimensioning and tolerancing per ANSI Y14.5M-1982.
2. "D" and "E1" do not include mold flashing. Mold flash or protrusions
shall not exceed .010 inch (0.25mm).
3. Terminal numbers are for reference only.
4. "C" dimension does not include solder finish thickness.
5. Symbol "N" is the maximum number of terminals.
4
2
2
5
D
4
1
5
8
E1
D1
E
e
A2
A
A1
C
L
B1
10
B
eB
PRODUCT SPECIFICATION
RV4140A
Mechanical Dimensions (continued)
8-Lead SOIC Package
Inches
Symbol
Min.
A
A1
B
C
D
E
e
H
h
L
N
a
ccc
Millimeters
Max.
Min.
Max.
.053
.069
.004
.010
.013
.020
.008
.010
.189
.197
.150
.158
.050 BSC
1.35
1.75
0.10
0.25
0.33
0.51
0.20
0.25
4.80
5.00
3.81
4.01
1.27 BSC
.228
.010
.016
5.79
0.25
0.40
.244
.020
.050
8
6.20
0.50
1.27
8
0¡
8¡
0¡
8¡
—
.004
—
0.10
8
Notes:
Notes
1. Dimensioning and tolerancing per ANSI Y14.5M-1982.
2. "D" and "E" do not include mold flash. Mold flash or
protrusions shall not exceed .010 inch (0.25mm).
3. "L" is the length of terminal for soldering to a substrate.
4. Terminal numbers are shown for reference only.
5
2
2
5. "C" dimension does not include solder finish thickness.
6. Symbol "N" is the maximum number of terminals.
3
6
5
E
1
H
4
h x 45¡
D
C
A1
A
SEATING
PLANE
e
B
–C–
LEAD COPLANARITY
a
L
ccc C
11
RV4140A
PRODUCT SPECIFICATION
Ordering Information
Part Number
Package
Operating Temperature Range
RV4140AN
8-Lead Plastic DIP
-35°C to +80°C
RV4140AM
8-Lead Plastic SOIC
-35°C to +80°C
LIFE SUPPORT POLICY
FAIRCHILD’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES
OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF FAIRCHILD SEMICONDUCTOR
CORPORATION. As used herein:
1. Life support devices or systems are devices or systems
which, (a) are intended for surgical implant into the body,
or (b) support or sustain life, and (c) whose failure to
perform when properly used in accordance with
instructions for use provided in the labeling, can be
reasonably expected to result in a significant injury of the
user.
2. A critical component in any component of a life support
device or system whose failure to perform can be
reasonably expected to cause the failure of the life support
device or system, or to affect its safety or effectiveness.
www.fairchildsemi.com
7/27/98 0.0m 002
Stock#DS20004140A
Ó 1998 Fairchild Semiconductor Corporation
www.fairchildsemi.com
RV4141A
Low Power Ground Fault Interrupter
Features
•
•
•
•
•
Powered from the AC line
Built-in rectifier
Direct interface to SCR
500 mA quiescent current
Precision sense amplifier
•
•
•
•
•
Adjustable time delay
Minimum external components
Meets UL 943 requirements
For use with 110V or 220V systems
Available in 8 pin DIP or SOIC package
Description
The RV4141A is a low power controller for AC receptacle
ground fault circuit interrupters. These devices detect hazardous current paths to ground and ground to neutral faults.
The circuit interrupter then disconnects the load from the
line before a harmful or lethal shock occurs.
Features not found in other GFCI controllers include a low
offset voltage sense amplifier eliminating the need for a coupling capacitor between the sense transformer and sense
amplifier, and an internal rectifier to eliminate high voltage
rectifying diodes.
Internally, the RV4141A contains a diode rectifier, shunt regulator, precision sense amplifier, current reference, time
delay circuit, and SCR driver.
The RV4141A is powered only during the positive half
period of the line voltage, but can sense current faults independent of its phase relative to the line voltage. The gate of
the SCR is driven only during the positive half cycle of the
line voltage.
Two sense transformers, SCR, solenoid, three resistors and
four capacitors complete the design of the basic circuit interrupter. The simple layout and minimum component count
insure ease of application and long term reliability.
Block Diagram
RV4141A
Amp Out
Cap
–
+
+
VFB
–
+
+
–
SCR
–
Delay
4.7K
VREF
+VS
Gnd
Line
65-4141-01
Rev. 1.0.0
PRODUCT SPECIFICATION
RV4141A
Pin Assignments
Amp Out
1
8
Delay Cap
VFB
2
7
SCR Trigger
VREF
3
6
+VS
GND
4
5
Line
65-4141A-02
Absolute Maximum Ratings
(beyond which the device may be damaged)1
Parameter
Min
Typ
Max
Units
Supply Current
10
mA
Internal Power Dissipation
500
mW
Storage Temperature Range
-65
+150
°C
Operating Temperature Range
-35
+80
°C
125°C
Junction Temperature
Lead Soldering Temperature
60 Sec, DIP
300
°C
10 Sec, SOIC
260
°C
Notes:
1. Functional operation under any of these conditions is NOT implied. Performance and reliability are guaranteed only if
Operating Conditions are not exceeded.
Thermal Characteristics
Parameter
qJA
2
Thermal resistance
Min
Typ
Max
Units
SOIC
240
°C/W
PDIP
160
°C/W
RV4141A
Electrical Characteristics
Parameters
PRODUCT SPECIFICATION
(ILINE = 1.5mA and TA = +25°C, RSET = 650kW)
Test Conditions
Min
Typ
Max
Units
Regulated Voltage
I2-3 = 11mA
25.0
27.0
29.0
V
Regulated Voltage
ILINE = 750 mA, I2-3 = 9mA
25.0
27.0
29.0
V
Quiescent Current
V5-4 = 24V
—
500
—
mA
-200
0
200
mV
—
1.5
—
MHz
30
100
nA
4.7
5.6
kW
Shunt Regulator (Pins 5 to 4)
Sense Amplifier (Pins 2 to 3)
Offset Voltage
Gain Bandwidth
(Design Value)
Input Bias Current
(Design Value)
SCR Trigger (Pins 7 to 4)
Output Resistance
V7-4 = Open, I2-3 = mA
3.8
Output Voltage
I2-3 = 9mA
0
0.1
10
mV
Output Voltage
I2-3 = 11mA
2.4
3.0
3.6
V
Output Current
V7-4 = 0V, I2-3 = 11mA
400
600
ILINE = 750 mA
12.0
13.0
14.0
V
mA
Reference Voltage (Pins 3 to 4)
Reference Voltage
Delay Timer (Pins 8 to 4)
Delay Time (Note 1)
C8-4 = 12nF
—
2.0
—
ms
Delay Current
I2-3 = 11mA
30
40
50
mA
Note:
1. Delay time is defined as starting when the instantaneous sense current (I2-3) exceeds 6.5 V/RSET and ending when the SCR
trigger voltage V7-6 goes high.
3
PRODUCT SPECIFICATION
Circuit Operation
(Refer to Block Diagram and Figure 1)
The precision op amp connected to Pins 1 through 3 senses
the fault current flowing in the secondary of the sense transformer, converting it to a voltage at Pin 1. The ratio of secondary current to output voltage is directly proportional to
feedback resistor, RSET.
RSET converts the sense transformer secondary current to a
voltage at Pin 1. Due to the virtual ground created at the
sense amplifier input by its negative feedback loop, the sense
transformer's burden is equal to the value of RIN. From the
transformer's point of view, the ideal value for RIN is 0W.
This will cause it to operate as a true current transformer
with minimal error. However, making RIN equal to zero creates a large offset voltage at Pin 1 due to the sense amplifier's
very high DC gain. RIN should be selected as high as possible consistent with preserving the transformer's operation as
a true current mode transformer. A typical value for RIN is
between 200 and 1000W.
As seen by the equation below, maximizing RIN minimizes
the DC offset error at the sense amplifiers output. The DC
offset voltage at Pin 1 contributes directly to the trip current
error. The offset voltage at Pin 1 is:
VOS x RSET/(RIN + RSEC)
Where:
VOS = Input offset voltage of sense amplifier
RSET = Feedback resistor
RIN = Input resistor
RSEC = Transformer secondary winding resistance
The sense amplifier has a specified maximum offset voltage
of 200 mV to minimize trip current errors.
Two comparators connected to the sense amplifier output are
configured as a window detector, whose references are -6.5
volts and +6.5 volts referred to Pin 3. When the sense transformer secondary RMS current exceeds 4.6/RSET the output
of the window detector starts the delay circuit. If the secondary current exceeds the predetermined trip current for longer
than the delay time a current pulse appears at Pin 7, triggering the SCR.
The SCR anode is directly connected to a solenoid or relay
coil. The SCR can be tripped only when its anode is more
positive than its cathode.
Supply Current Requirements
The RV4141A is powered directly from the line through a
series limiting resistor called RLINE, its value is between
24 kW and 91 kW. The controller IC has a built-in diode
rectifier eliminating the need for external power diodes.
4
RV4141A
The recommended value for RLINE is 24 kW to 47 kW for
110V systems and 47 kW to 91 kW for 220V systems. When
RLINE is 47 kW the shunt regulator current is limited to
3.6 mA. The recommended maximum peak line current
through RLINE is 10 mA.
GFCI Application (Refer to Figure 1)
The GFCI detects a ground fault by sensing a difference current in the line and neutral wires. The difference current is
assumed to be a fault current creating a potentially hazardous
path from iine to ground. Since the line and neutral wires
pass through the center of the sense transformer, only the differential primary current is transferred to the secondary.
Assuming the turns ratio is 1:1000 the secondary current is
1/1000th the fault current. The RV4141A’s sense amplifier
converts the secondary current to a voltage which is compared with either of the two window detector reference voltages. If the fault current exceeds the design value for the
duration of the programmed time delay, the RV4141A will
send a current pulse to the gate of the SCR.
Detecting ground to neutral faults is more difficult. RB represents a normal ground fault resistance, RN is the wire resistance of the electrical circuit between load/ neutral and earth
ground. RG represents the ground to neutral fault condition.
According to UL 943, the GFCI must trip when RN = 0.4W,
RG = 1.6W and the normal ground fault is 6 mA.
Assuming the ground fault to be 5 mA, 1 mA and 4 mA will
go through RG and RN, respectively, causing an effective 1
mA fault current. This current is detected by the sense transformer and amplified by the sense amplifier. The ground/
neutral and sense transformers are now mutually coupled by
RG, RN and the neutral wire ground loop, producing a positive feedback loop around the sense amplifier. The newly
created feedback loop causes the sense amplifier to oscillate
at a frequency determined by ground/neutral transformer
secondary inductance and C4. Typically it occurs at 8 KHz.
C2 is used to program the time required for the fault to be
present before the SCR is triggered. Refer to the equation
below for calculating the value of C2. Its typical value is 12
nF for a 2 ms delay.
RSET is used to set the fault current at which the GFCI trips.
When used with a 1:1000 sense transformer, its typical value
is 1 MW for a GFCI designed to trip at 5 mA.
RIN should be the highest value possible which insures a
predictable secondary current from the sense transformer. If
RIN is set too high, normal production variations in the
transformer permeability will cause unit to unit variations in
the secondary current. If it is too low, a large offset voltage
error at Pin 1 will be present. This error voltage in turn creates a trip current error proportional to the input offset voltage of the sense amplifier. As an example, if RIN is 500W,
RV4141A
PRODUCT SPECIFICATION
Calculating The Values Of RSET and C2
RSET is 1 MW, RSEC is 45W and the VOS of the sense amplifier is its maximum of 200 mV, the trip current error is
±5.6%.
Determine the nominal ground fault trip current requirement.
This will be typically 5 mA in North America (117V AC)
and 22 mA in the UK and Europe (220V AC). Determine the
minimum delay time required to prevent nuisance tripping.
This will typically be 1 to 2 ms. The value of C2 required to
provide the desired delay time is:
The SCR anode is directly connected to a solenoid or relay
coil. It can be tripped only when its anode is more positive
than its cathode. It must have a high dV/dt rating to ensure
that line noise (generated by electrically noisy appliances)
does not falsely trigger it. Also the SCR must have a gate
drive requirement less than 200 mA. C3 is a noise filter that
prevents high frequency line pulses from triggering the SCR.
C2 = 6 x T
where:
C2 is in nF
T is the desired delay time in ms.
The relay solenoid used should have a response time of 3 ms
or less to meet the UL 943 timing requirement.
The value of RSET to meet the nominal ground fault trip current specification is:
Sense Transformers and Cores
The sense and ground/neutral transformer cores are usually
fabricated using high permeability laminated steel rings.
Their single turn primary is created by passing the line and
neutral wires through the center of its core. The secondary is
usually from 200 to 1500 turns.
4.6 ´ N
R SET = --------------------------------------------------------------I FAULT ´ COS 180 ( T ¤ P )
where:
RSET is in kW
T is the time delay in ms
P is the period of the line frequency in ms
IFAULT is the desired ground fault trip current in mA RMS
N is the number of sense transformer secondary turns.
Magnetic Metals Corporation, Camden, NJ 08101,
(609) 964-7842 and Magnetics, 900 E. Butler Road, P.O.
Box 391, Butler, PA 16003, (412) 282-8282 are full-line suppliers of ring cores and transformers designed specifically
for GFCI and related applications.
This formula assumes an ideal sense transformer is used.
The calculated value of RSET may have to be changed up to
30% to when using a non-ideal transformer.
Press to
RTEST
Mov
Test
15K
Sense Transformer
1:1000
5 Ring Steel Core
Grounded Neutral
1:200
Normally Closed
Latching Contacts
Phase
Line
Load
Neutral
Solenoid
RN
0.4
C4
R IN
470
RB
20K
1000 pF
C1
10 nF
R SET
C2
8
1
1.1 Meg
2
Q1
TAG
X0103DA
7
RV4141A
3
6
4
5
12 nF
CF
+
C3
10 nF
R LINE
24K
1W
RG
1.6
Fault
Resistance
Not Part of
Application
1µF 35V
1N4004
GFCI
Note:
1. Portions of this schematic are subject to U.S. patents 3,878,435 and Re. 30,678.
65-4141A-03
Figure 1. GFI Application Circuit
5
PRODUCT SPECIFICATION
RV4141A
Mechanical Dimensions
8-Lead Plastic DIP Package
Inches
Symbol
A
A1
A2
B
B1
C
D
D1
E
E1
e
eB
L
Millimeters
Min.
Max.
Min.
Max.
—
.015
.115
.014
.045
.008
.348
.005
.300
.240
.210
—
.195
.022
.070
.015
.430
—
.325
.280
—
.38
2.93
.36
1.14
.20
8.84
.13
7.62
6.10
5.33
—
4.95
.56
1.78
.38
10.92
—
8.26
7.11
.100 BSC
—
.430
.115
.160
2.54 BSC
—
10.92
2.92
4.06
8¡
8¡
N
Notes:
Notes
1. Dimensioning and tolerancing per ANSI Y14.5M-1982.
2. "D" and "E1" do not include mold flashing. Mold flash or protrusions
shall not exceed .010 inch (0.25mm).
3. Terminal numbers are for reference only.
4. "C" dimension does not include solder finish thickness.
5. Symbol "N" is the maximum number of terminals.
4
2
2
5
D
4
1
5
8
E1
D1
E
e
A2
A
A1
C
L
B1
6
B
eB
RV4141A
PRODUCT SPECIFICATION
Mechanical Dimensions (continued)
8-Lead SOIC Package
Inches
Symbol
Min.
A
A1
B
C
D
E
e
H
h
L
N
a
ccc
Millimeters
Max.
Min.
Max.
.053
.069
.004
.010
.013
.020
.008
.010
.189
.197
.150
.158
.050 BSC
1.35
1.75
0.10
0.25
0.33
0.51
0.20
0.25
4.80
5.00
3.81
4.01
1.27 BSC
.228
.010
.016
5.79
0.25
0.40
.244
.020
.050
8
6.20
0.50
1.27
8
0¡
8¡
0¡
8¡
—
.004
—
0.10
8
Notes:
Notes
1. Dimensioning and tolerancing per ANSI Y14.5M-1982.
2. "D" and "E" do not include mold flash. Mold flash or
protrusions shall not exceed .010 inch (0.25mm).
3. "L" is the length of terminal for soldering to a substrate.
4. Terminal numbers are shown for reference only.
5
2
2
5. "C" dimension does not include solder finish thickness.
6. Symbol "N" is the maximum number of terminals.
3
6
5
E
1
H
4
h x 45¡
D
C
A1
A
SEATING
PLANE
e
B
–C–
LEAD COPLANARITY
a
L
ccc C
7
PRODUCT SPECIFICATION
RV4141A
Ordering Information
Part Number
Package
Operating Temperature Range
RV4141AN
8-Lead Plastic DIP
-35°C to +80°C
RV4141AM
8-Lead Plastic SOIC
-35°C to +80°C
LIFE SUPPORT POLICY
FAIRCHILD’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES
OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF FAIRCHILD SEMICONDUCTOR
CORPORATION. As used herein:
1. Life support devices or systems are devices or systems
which, (a) are intended for surgical implant into the body,
or (b) support or sustain life, and (c) whose failure to
perform when properly used in accordance with
instructions for use provided in the labeling, can be
reasonably expected to result in a significant injury of the
user.
2. A critical component in any component of a life support
device or system whose failure to perform can be
reasonably expected to cause the failure of the life support
device or system, or to affect its safety or effectiveness.
www.fairchildsemi.com
5/20/98 0.0m 001
Stock#DS2004141A
Ó 1998 Fairchild Semiconductor Corporation
Embedded Secure Document
The file http://www.fairchildsemi.com/ds/RV/RV4141a.pdf is a secure document that has been
embedded in this document. Double click the pushpin to view RV4141a.pdf.
www.fairchildsemi.com
RV4145A
Low Power Ground Fault Interrupter
Features
•
•
•
•
No potentiomenter required
Direct interface to SCR
Supply voltage derived from AC line – 26V shunt
Adjustable sensitivity
•
•
•
•
Grounded neutral fault detection
Meets U.L. 943 standards
450mA quiescent current
Ideal for 120V or 220V systems
Description
The RV4145A is a low power controller for AC outlet
ground fault interrupters. These devices detect hazardous
grounding conditions, such as equipment (connected to
opposite phases of the AC line) in contact with a pool of
water and open circuits the line before a harmful or lethal
shock occurs.
Contained internally are a 26V zener shunt regulator, an op
amp, and an SCR driver. WIth the addition of two sense
transformers, a bridge rectifier, an SCR, a relay, and a few
additional components, the RV4145A will detect and protect
against both hot wire to ground and neutral wire to ground
faults. The simple layout and conventional design ensure
ease of application and long-term reliability.
Block Diagram
RV4145A
VFB
+Input
R1
10K
Op Amp Output
R2
10K
VREF
(+13V)
6.5V
6.5V
6.5V
6.5V
Ground
+VS
(+26V)
SCR Trigger
R3
4.7K
65-4145A-01
Rev. 1.0.2
PRODUCT SPECIFICATION
RV4145A
Pin Assignments
NC
VFB
1
8
+Input
2
7
Op Amp Output
VREF
3
6
+VS
GND
4
5
SCR Trigger
65-4145A-02
Absolute Maximum Ratings
(beyond which the device may be damaged)1
Parameter
Min
Max
Units
Supply Current
18
mA
Internal Power Dissipation
500
mW
+150
°C
+85
°C
Storage Temperature Range
-65
Operating Temperature Range
-35
Typ
125°C
Junction Temperature
Lead Soldering Temperature
PD TA < 50°C
60 Sec, DIP
300
°C
10 Sec, SOIC
260
°C
SOIC
300
mW
PDIP
For TA > 50°C Derate at
468
mW
SOIC
4.1
mW/°C
PDIP
6.25
mW/°C
Notes:
1. Functional operation under any of these conditions is NOT implied. Performance and reliability are guaranteed only if
Operating Conditions are not exceeded.
Operating Conditions
Parameter
qJA
2
Thermal resistance
Min
Typ
Max
Units
SOIC
240
°C/W
PDIP
160
°C/W
RV4145A
Electrical Characteristics
PRODUCT SPECIFICATION
(IS = 1.5mA and TA = +25°C)
Parameters
Test Conditions
Min
Typ
Max
Units
Detector Reference Voltage
Pin 7 to Pin 3
6.8
7.2
8.1
±V
Zener Voltage (+VS)
Pin 6 to Pin 4
25
26
29.2
V
Reference Voltage (VREF)
Pin 3 to Pin 4
12.5
13
14.6
V
Quiescent Current (IS)
+VS = 24V
450
750
mA
Shunt Regulator
Operational Amplifier
Offset Voltage
Pin 2 to Pin 3
-3.0
0.5
+3.0
mV
+Output Voltage Swing
Pin 7 to Pin 3
6.8
7.2
8.1
V
–Output Voltage Swing
Pin 7 to Pin 3
-9.5
-11.2
-13.5
V
+Output Source Current
Pin 7 to Pin 3
–Output Source Current
Pin 7 to Pin 3
Gain Bandwidth Product
F = 50KHz
Resistors
IS = 0mA
R1
mA
650
1.0
mA
1.8
MHz
Pin 1 to Pin 3
10
kW
R2
Pin 2 to Pin 3
10
kW
R3
Pin 5 to Pin 4
SCR Trigger Voltage
Pin 5 to Pin 4
1.0
4.7
Detector On
1.5
2.8
Detector Off
0
1
10
mV
Electrical Characteristics
5.9
kW
3.5
V
(IS = 1.5mA and -35°C £ TA £ +85°C)
Parameters
Test Conditions
Min
Typ
Max
Units
Detector Reference Voltage
Pin 7 to Pin 3
6.5
7.2
8.3
±V
Zener Voltage (+VS)
Pin 6 to Pin 4
24
26
30
V
Reference Voltage (VREF)
Pin 3 to Pin 4
12
13
15
V
Quiescent Current (IS)
+VS = 23V
Shunt Regulator
mA
500
Operational Amplifier
Offset Voltage
Pin 2 to Pin 3
-5.0
+Output Voltage Swing
Pin 7 to Pin 3
6.5
–Output Voltage Swing
Pin 7 to Pin 3
-9
Gain Bandwidth Product
F = 50KHz
Resistors
IS = 0mA
R1
Pin 1 to Pin 3
R2
Pin 2 to Pin 3
R3
Pin 5 to Pin 4
SCR Trigger Voltage
Pin 5 to Pin 4
0.5
+5.0
mV
7.2
8.3
V
-11.2
-14
V
1.8
MHz
10
kW
kW
10
3.5
4.7
Detector On
1.3
2.8
Detector Off
0
3
5.9
kW
V
50
mV
3
PRODUCT SPECIFICATION
Principles of Operation
The 26V shunt regulator voltage generated by the string of
zener diodes is divided into three reference voltages: 3/4 VS,
1/2 VS, and 1/4 VS. VREF is at 1/2VS and is used as a reference to create an artifical ground of +13V at the op amp noninverting input.
Figure 1 shows a three-wire 120V AC outlet GFI application
using an RV4145A. Fault signals from the sense transformer
are AC coupled into the input and are amplified according to
the following equation:
V7 = RSENSE ´ ISENSE/N
Where V7 is the RMS voltage at pin 7 relative to pin 3,
RSENSE is the value of the feedback resistor connected from
pin 7 to pin 1, ISENSE is the fault current in amps RMS and
N is the turns ratio of the transformer. When V7 exceeds plus
or minus 7.2V relative to pin 3 the SCR Trigger output will
go high and fire the external SCR.
The formula for V7 is approximate because it does not
include the sense transformer characteristics.
Grounded neutral fault detection is accomplished when a
short or fault closes a magnetic path between the sense transformer and the grounded neutral transformer. The resultant
AC coupling closes a positive feedback path around the op
amp, and therefore the op amp oscillates. When the peaks of
the oscillation voltage exceed the SCR trigger comparator
thresholds, the SCR output will go high.
Shunt Regulator
RLINE limits the current into the shunt regulator; 220V
applications will require substituting a 47kW 2W resistor. In
addition to supplying power to the IC, the shunt regulator
creates internal reference voltages (see above).
Operational Amplifier
RSENSE is a feedback resistor that sets gain and therefore
sensitivity to normal faults. To adjust RSENSE, follow this
procedure: apply the desired fault current (a difference in
current of 5mA is the UL 943 standard). Adjust RSENSE
upward until the SCR activates. A fixed resistor can be used
for RSENSE, since the resultant ±15% variation in sensitivity
will meet UL’s 943 4-6mA specification window.
4
RV4145A
The roll-off frequency is greater than the grounded neutral
fault oscillation frequency, in order to preserve loop gain for
oscillation (which is determined by the inductance of the
200:1 transformer and C4).
The senstivity to grounded neutral faults is adjusted by
changing the frequency of oscillation. Increasing the frequency reduces the sensitivity by reducing the loop gain of
the positive feedback circuit. As frequency increases, the
signal becomes attenuated and the loop gain decreases. With
the values shown the circuit will detect a grounded neutral
fault having resistance of 2W or less.
The input to the op amp are protected from overvoltage by
back-toback diodes.
SCR Driver
The SCR used must have a high dV/dt rating to ensure that
line noise (generated by noisy appliances such as a drill
motor) does not falsely trigger the SCR. Also, the SCR must
have a gate drive requirement of less than 200mA. CF is a
noise filter capacitor that prevents narrow pulses from firing
the SCR.
The relay solenoid used should have a 3ms or less response
time in order to meet the UL 943 timing requirement.
Sense Transformers and Cores
The sense and grounded neutral transformer cores are usually fabricated using high permeability laminated steel rings.
Their single turn primary is created by passing the line and
neutral wires through the center of its core. The secondary is
usually from 200 to 1500 turns.
Magnetic Metals Corporation, Camden, NJ 08101,
(609) 964-7842, and Magnetics, 900 E. Butler Road,
P.O. Box 391, Butler, PA 16003, (412) 282-8282 are full line
suppliers of ring cores and transformers designed specifically for GFI applications.
Two-Wire Application Circuit
Figure 2 shows the diagram of a 2-wire 120V AC outlet GFI
circuit using an RV4145A. This circuit is not designed to
detect grounded neutral faults. Thus, the grounded neutral
transformer and capacitors C3 and C4 of Figure 1 are not
used.
RV4145A
PRODUCT SPECIFICATION
Press
To Test
RTEST
15K
Mov
Ground Neutral
Transformer
Sense Transformer
1000:1
Line
Latching
Contacts
K1
200:1
Hot
Neutral
RSENSE
1M *
C1
10µF
Load
C3
0.01 µF
RV4145
VFB
Op Amp Output
VREF (+13V)
GND
Solenoid
C4
0.03 µF
+VS
SCR Trigger
DB1
1N4004 (4)
RLINE
24K
Q1 MOT
MCR100-6
CF
2.2 µF
C2
0.01µF
65-4145A-03
* Value depends on transformer characteristics.
Figure 1. GFI Application Circuit (Three-Wire Outlet)
5
PRODUCT SPECIFICATION
RV4145A
Press
To Test
RTEST
15K
Mov
Sense Transformer
1000:1
Line
Latching
Contacts
K1
Hot
Neutral
RSENSE
1M *
C1
10µF
Load
RV4145
VFB
Op Amp Output
VREF (+13V)
GND
Solenoid
+VS
SCR Trigger
DB1
1N4004 (4)
RLINE
24K
Q1 Tag
X0103DA
CF
2.2 µF
C2
0.01µF
65-4145A-04
* Value depends on transformer characteristics.
Figure 2. GFI Application Circuit (Two-Wire Outlet)
6
+Input
(2)
VFB
(1)
Q21
10 pF
C2
Q22
(-)
R1
10K
Q4
Q1
R4
50K
Q6
Q3
R10
6K
Q5
Q2
Q7
R5
50K
(+)
R2
10K
Q8
4 pF
C1
Q9
Q23
Q11
Q10
R6
450
R14
1.3K
Q12
Q14
(7)
Z1
5.6V
Q15
R3
4.7K
R13
30K
Op Amp Output
R9
39K
Q13
R7
250K
Q17
6.5V
(5)
Ground
(4)
VREF
(+13V)
(3)
+VS (+26V)
65-4145A-05
SCR Trigger
Substrate
R12
7.2K
Q16
Q18
6.5V
Q19
6.5V
Q20
6.5V
(6)
RV4145A
PRODUCT SPECIFICATION
Schematic Diagram
7
PRODUCT SPECIFICATION
Notes:
8
RV4145A
RV4145A
PRODUCT SPECIFICATION
Notes:
9
PRODUCT SPECIFICATION
RV4145A
Mechanical Dimensions
8-Lead Plastic DIP Package
Inches
Symbol
A
A1
A2
B
B1
C
D
D1
E
E1
e
eB
L
Millimeters
Min.
Max.
Min.
Max.
—
.015
.115
.014
.045
.008
.348
.005
.300
.240
.210
—
.195
.022
.070
.015
.430
—
.325
.280
—
.38
2.93
.36
1.14
.20
8.84
.13
7.62
6.10
5.33
—
4.95
.56
1.78
.38
10.92
—
8.26
7.11
.100 BSC
—
.430
.115
.160
2.54 BSC
—
10.92
2.92
4.06
8¡
8¡
N
Notes:
Notes
1. Dimensioning and tolerancing per ANSI Y14.5M-1982.
2. "D" and "E1" do not include mold flashing. Mold flash or protrusions
shall not exceed .010 inch (0.25mm).
3. Terminal numbers are for reference only.
4. "C" dimension does not include solder finish thickness.
5. Symbol "N" is the maximum number of terminals.
4
2
2
5
D
4
1
5
8
E1
D1
E
e
A2
A
A1
C
L
B1
10
B
eB
RV4145A
PRODUCT SPECIFICATION
Mechanical Dimensions (continued)
8-Lead SOIC Package
Inches
Symbol
Min.
A
A1
B
C
D
E
e
H
h
L
N
a
ccc
Millimeters
Max.
Min.
Max.
.053
.069
.004
.010
.013
.020
.008
.010
.189
.197
.150
.158
.050 BSC
1.35
1.75
0.10
0.25
0.33
0.51
0.20
0.25
4.80
5.00
3.81
4.01
1.27 BSC
.228
.010
.016
5.79
0.25
0.40
.244
.020
.050
8
6.20
0.50
1.27
8
0¡
8¡
0¡
8¡
—
.004
—
0.10
8
Notes:
Notes
1. Dimensioning and tolerancing per ANSI Y14.5M-1982.
2. "D" and "E" do not include mold flash. Mold flash or
protrusions shall not exceed .010 inch (0.25mm).
3. "L" is the length of terminal for soldering to a substrate.
4. Terminal numbers are shown for reference only.
5
2
2
5. "C" dimension does not include solder finish thickness.
6. Symbol "N" is the maximum number of terminals.
3
6
5
E
1
H
4
h x 45¡
D
C
A1
A
SEATING
PLANE
e
B
–C–
LEAD COPLANARITY
a
L
ccc C
11
PRODUCT SPECIFICATION
RV4145A
Ordering Information
Part Number
Package
Operating Temperature Range
RV4145AN
8-Lead Plastic DIP
-35°C to +85°C
RV4145AM
8-Lead Plastic SOIC
-35°C to +85°C
LIFE SUPPORT POLICY
FAIRCHILD’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES
OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF FAIRCHILD SEMICONDUCTOR
CORPORATION. As used herein:
1. Life support devices or systems are devices or systems
which, (a) are intended for surgical implant into the body,
or (b) support or sustain life, and (c) whose failure to
perform when properly used in accordance with
instructions for use provided in the labeling, can be
reasonably expected to result in a significant injury of the
user.
2. A critical component in any component of a life support
device or system whose failure to perform can be
reasonably expected to cause the failure of the life support
device or system, or to affect its safety or effectiveness.
www.fairchildsemi.com
5/20/98 0.0m 001
Stock#DS2004145A
Ó 1998 Fairchild Semiconductor Corporation
Embedded Secure Document
The file http://www.fairchildsemi.com/ds/RV/RV4145a.pdf is a secure document that has been
embedded in this document. Double click the pushpin to view RV4145a.pdf.
RV4146
RV4146
Low Power Ground Fault Interrupter
Description
Features
The RV4146 is a low power controller for AC
receptacle ground fault circuit interrupters. These
devices detect hazardous current paths to ground and
ground to neutral faults. The circuit interrupter then
disconnects the load from the line before a harmful or
lethal shock occurs.
◆
◆
◆
◆
◆
◆
◆
◆
◆
◆
◆
Internally, the RV4146 contains an oscillator, shunt
regulator, precision sense amplifier, current reference,
time delay circuit, and SCR driver.
Two sense transformers, SCR, solenoid, four diodes,
three resistors and four capacitors complete the
design of the basic circuit interrupter. The simple
layout and minimum component count insure ease of
application and long term reliability.
Features not found in other GFCI controllers include a
low offset voltage sense amplifier, eliminating the need
for a coupling capacitor between the sense
transformer and sense amplifier, and an internal
oscillator to eliminate the sensitivities of the dormant
oscillator
Built-in grounded neutral oscillator
Direct interface to SCR
1 mA quiescent current
Precision sense amplifier
Adjustable time delay
Minimum external components
Meets UL 943 requirements
For use with 110V or 220V systems
Available in 8 pin DIP or SOIC package
Differential circuitry for noise immunity
Trip time dependent on fault magnitude
The RV4146 senses current faults independent of its
phase relative to the line voltage. The gate of the SCR
is driven during both cycles of the line voltage.
Noise immunity is maximized on the RVxxxx, but the
use of differential circuitry with 3 times the discharge
current as charge, and low output impedance on the
SCR driver.
Functional Block Diagram
Amp Out
RV4146
1
8
Cap
7
SCR
6
+VS
5
Osc Out
–
+
VFB
2
VREF
3
Gnd
4
–
+
Delay
+
–
+
–
4.7K
10 KHz
Osc
65-????
For More Information, call 1-888-522-5372
Fairchild Semiconductor
3-1
RV4146
Absolute Maximum Ratings
Supply Current ........................................ 10 mA
Internal Power Dissipation.................... 500 mW
Storage Temperature
Range ................................ -65°C to +150°C
Operating Temperature
Range .................................. -35°C to +80°C
Lead Soldering Temperature
(60 Sec., DIP) ................................... +300°C
(10 Sec., SO) ................................... +260°C
Connection Information
Ordering Information
Part Number
Package
Operating
Temperature
Range
N
M
-35°C to +80°C
-35°C to +80°C
RV4146N
RV4146M
Notes:
N = 8-lead plastic DIP
M = 8-lead plastic SOIC
Thermal Characteristics
8-Lead
Plastic
SOIC
8-Lead
Plastic
DIP
Max. Junction Temp.
+125°C
+125°C
300 mW
468 mW
8-Lead Plastic
Dual In-Line SO-8
(Top View)
1
8
2
7
Max. PD TA <50°C
3
6
Therm. Res θJC
—
—
4
5
Therm. Res. θJA
240°C/W
160°C/W
For TA >50°C
Derate at
4.1 mW
per °C
6.25 mW
per °C
65-02666
8-Lead Plastic
Dial In-Line Package
(Top View)
1
8
2
7
3
6
4
5
65-0093
Pin
1
2
3
4
5
6
7
8
3-2
Function
Amp Out
VFB
VREF (+13V)
Ground
Line
+VS
SCR Trigger
Delay Cap
Fairchild Semiconductor
For More Information, call 1-888-522-5372
RV4146
MOV
Sense Transformer
1:1000
RTest
Press to
15K
Test
Grounded Neutral
1:200
5 Ring Steel Core
Hot
Normally Closed
Line
Load
Neutral
Solenoid
C4
RLine
1000pF
+
15K 1/2W
Rin
470
C1
4700pF
Rset
1
8
Q1
SCR
400V @ .8A
NC
1.1Meg
2
7
RV4146
3
6
+
4
5
CF
1µF
35V
+
C3
2.2µF
10V
C2
.01µF
250V
Internal Osc
Figure 1. GFI Application Circuit (Full-Wave)
For More Information, call 1-888-522-5372
Fairchild Semiconductor
3-3
RV4146
Electrical Characteristics
(ILINE = 2.5 mA and TA = +25°C, RSET = 650 kΩ)
Parameters
Shunt Regulator (Pins 6 to 4)
Regulated Voltage
Regulated Voltage
Quiescent Current
Sense Amplifier (Pins 2 to 3)
Offset Voltage
Gain Bandwidth
Input Bias Current
SCR Trigger (Pins 7 to 4)
Output Voltage
Output Voltage
Output Current
Reference Voltage (Pins 3 to 4)
Reference Voltage
Delay Timer (Pins 8 to 4)
Delay Time (Note 1)
Delay Current
Oscillator
Frequency
Voltage
Output Current
Test Conditions
Min
Typ
Max
Units
I2-3 = 11 µA
ILINE = 750 µA, I2-3 = 9 µA
V5-4 = 24V
25.0
25.0
—
27.0
27.0
51
29.0
29.0
—
Volts
Volts
mA
250
—
0
1.5
30
250
—
100
µV
MHz
nA
I2-3 = 9 µA
I2-3 = 11 µA
V7-4 = 0V, I2-3 = 11 µA
0
2.4
500
0.1
3.0
1000
.2
3.6
2500
V
Volts
µA
ILINE = 750 µA
12.0
13.0
14.0
Volts
C8-4 = 12 nF
I2-3 = 11 µA
—
30
2.0
40
—
50
ms
µA
5
10
1.5
4
15
KHz
V
mA
(Design Value)
(Design Value)
2
Note:
1. Delay time is defined as starting when the instantaneous sense current (I2-3) exceeds 6.5 V/RSET and ending when the SCR
trigger voltage V7-6 goes high.
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Fairchild Semiconductor
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RV4146
Circuit Operation
Supply Current Requirements
(Refer to Block Diagram and Figure 1)
The RV4146 is powered directly from the line through
a series limiting resistor called RLINE, of 15 kΩ. The
controller IC requires and external full wave bridge
diode.
The precision op amp connected to Pins 1 through 3
senses the fault current flowing in the secondary of the
sense transformer, converting it to a voltage at Pin 1.
The ratio of secondary current to output voltage is
directly proportional to feedback resistor, RSET .
RSET converts the sense transformer secondary
current to a voltage at Pin 1. Due to the virtual ground
created at the sense amplifier input by its negative
feedback loop, the sense transformer’s burden is
equal to the value of RIN. From the transformer's point
of view, the ideal value for RIN is 0Ω. This will cause it
to operate as a true current transformer with minimal
error. However, making RIN equal to zero creates a
large offset voltage at Pin 1 due to the sense
amplifier's very high DC gain. RIN should be selected
as high as possible consistent with preserving the
transformer's operation as a true current mode
transformer. A typical value for RIN is between 200
and 1000Ω.
As seen by the equation below, maximizing RIN
minimizes the DC offset error at the sense amplifiers
output. The DC offset voltage at Pin 1 contributes
directly to the trip current error. The offset voltage at
Pin 1 is:
VOS x RSET/(RIN + RSEC)
Where:
VOS = Input offset voltage of sense amplifier
RSET = Feedback resistor
RIN = Input resistor
RSEC= Transformer secondary winding resistance
The sense amplifier has a specified maximum offset
voltage of 200 µV to minimize trip current errors.
Two comparators connected to the sense amplifier
output are configured as a window detector, whose
references are -6.5 volts and +6.5 volts referred to Pin
3. When the sense transformer secondary RMS
current exceeds 4.6/RSET the output of the window
detector starts the delay circuit. If the secondary
current exceeds the predetermined trip current for
longer than the delay time a current pulse appears at
Pin 7, triggering the SCR.
The SCR anode is directly connected to a solenoid or
relay coil. The SCR can be tripped only when its
anode is more positive than its cathode.
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The recommended value for RLINE is 15 kΩ for 110V
systems and 36 kΩ for 220V systems. When RLINE is
30 kΩ the shunt regulator current is limited to 5 mA.
The recommended maximum peak line current
through RLINE is 15 mA.
GFCI Application
(Refer to Figure 1)
The GFCI detects a ground fault by sensing a
difference current in the line and neutral wires. The
difference current is assumed to be a fault current
creating a potentially hazardous path from line to
ground. Since the line and neutral wires pass through
the center of the sense transformer, only the
differential primary current is transferred to the
secondary. Assuming the turns ratio is 1:1000 the
secondary current is 1/1000th the fault current. The
RV4146’s sense amplifier converts the secondary
current to a voltage which is compared with either of
the two window detector reference voltages. If the fault
current exceeds the design value for the duration of
the programmed time delay, the RV4146 will send a
current pulse to the gate of the SCR.
Detecting ground to neutral faults is more difficult. RB
represents a normal ground fault resistance, RN is the
wire resistance of the electrical circuit between load/
neutral and earth ground. RG represents the ground to
neutral fault condition. According to UL 943, the GFCI
must trip when RN = 0.4Ω, RG = 1.6Ω and the normal
ground fault is 6 mA.
Assuming the ground fault to be 5 mA, 1 mA and 4 mA
will go through RG and RN, respectively, causing an
effective 1 mA fault current. This current is detected by
the sense transformer and amplified by the sense
amplifier. The ground/neutral and sense transformers
are mutually coupled by RG, RN and the neutral wire
ground loop, through the use of an on-board 10KHz
oscillator.
C2 is used to program the time required for the fault to
be present before the SCR is triggered. Refer to the
equation below for calculating the value of C2. Its
typical value is 12 nF for a 2 ms delay.
Fairchild Semiconductor
3-5
RV4146
RSET is used to set the fault current at which the GFCI
trips. When used with a 1:1000 sense
transformer, its typical value is 1 MΩ for a GFCI
designed to trip at 5 mA.
RIN should be the highest value possible which
insures a predictable secondary current from the
sense transformer. If RIN is set too high, normal
production variations in the transformer permeability
will cause unit to unit variations in the secondary
current. If it is too low, a large offset voltage error at
Pin 1 will be present. This error voltage in turn creates
a trip current error proportional to the input offset
voltage of the sense amplifier. As an example, if RIN is
500Ω, RSET is 1 MΩ, RSEC is 45Ω and the VOS of the
sense amplifier is its maximum of 200 µV, the trip
current error is ±5.6%.
The SCR anode is directly connected to a solenoid or
relay coil. It can be tripped only when its anode is
more positive than its cathode. It must have a high dV/
dt rating to ensure that line noise (generated by
electrically noisy appliances) does not falsely trigger it.
Also the SCR must have a gate drive requirement less
than 200 µA. C3 is a noise filter that prevents high
frequency line pulses from triggering the SCR.
The relay solenoid used should have a response time
of 3 ms or less to meet the UL 943 timing requirement.
Sense Transformers and Cores
The sense and ground/neutral transformer cores are
usually fabricated using high permeability laminated
steel rings. Their single turn primary is created by
passing the line and neutral wires through the center
of its core. The secondary is usually from 200 to 1500
turns.
Calculating The Values of RSET and C2
Determine the nominal ground fault trip current
requirement. This will be typically 5 mA in North
America (117V AC) and 22 mA in the UK and Europe
(220V AC).
Determine the minimum delay time required to prevent
nuisance tripping. This will typically be 1 to 2 ms.
The value of C2 required to provide the desired delay
time is:
C2 = 6 x T
where:
C2 is in nF
T is the desired delay time in ms.
The value of RSET to meet the nominal ground fault
trip current specification is:
4.6 x N
RSET =
IFAULT x COS 180(T/P)
Where:
RSET is in kΩ
T is the time delay in ms
P is the period of the line frequency in ms
IFAULT is the desired ground fault trip current
in mA RMS
N is the number of sense transformer
secondary turns.
This formula assumes an ideal sense transformer is
used. The calculated value of RSET may have to be
changed up to 30% to when using a non-ideal
transformer.
Magnetic Metals Corporation, Camden, NJ 08101,
(609) 964-7842 and Magnetics, 900 E. Butler Road,
P.O. Box 391, Butler, PA 16003, (412) 282-8282 are
full-line suppliers of ring cores and transformers
designed specifically for GFCI and related
applications.
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Fairchild Semiconductor
For More Information, call 1-888-522-5372