FAN4146 Fairchild Semiconductor, FAN4146 Datasheet - Page 5

• Manufacturer Part Number: FAN4146
• Description: The FAN4146 is a low-power controller for AC outlet Appliance Leakage Circuit Interrupters (ALCI) and two-wire Residual Current Devices (RCD)
• Manufacturer: Fairchild Semiconductor

© 2010 Fairchild Semiconductor Corporation
FAN4146 • Rev. 1.0.0
Functional Description
Refer to Figure 1 and Figure 3.
The FAN4146 is a two-wire GFCI controller for AC
ground-fault-circuit interrupters. The internal rectifier
circuit is biased by the AC line during the positive half
cycle of the AC line voltage. The internal 12V shunt
regulator uses a precision temperature-compensated
bandgap reference. The combination of precision
reference circuitry and precision sense amplifier
provides for an accurate ground-fault tolerance. This
allows for selection of external components with wider
and lower-cost parameter variation. Due to the low
quiescent current, a high value external series resistor
(R
wattage required for this resistor. The 12V shunt
regulator generates the reference voltage V
sense amplifier’s (A
reference) and supplies the bias for the delay timer (t
comparators (C
The secondary winding of the sense transformer is
directly DC coupled to the inverting input of the sense
amplifier at pin 5 (V
sense transformer’s secondary current to a voltage at
pin 6 (AmpOut). This voltage is compared to the internal
window comparator (C
voltage exceeds the +/-V
window comparator triggers the internal delay timer.
The output of the window comparator must stay HIGH
for the duration of the t
comparator’s output momentarily goes LOW, the t
timer resets. If the window comparator’s output is still
HIGH at the end of the t
the current source I
source I
energizes the solenoid, opens the contact switches to
the load, and removes the hazardous ground fault. The
window comparator allows detection of a positive or
negative I
the line voltage. An internal under-voltage lockout circuit
disables the SCR driver if the voltage at pin 3 (LINE) is
below 7.5V. This prevents the SCR from energizing the
solenoid when the SCR’s anode voltage is below 65V.
The sense transformer typically has a toroidal core
made of laminated steel rings or solid ferrite material.
The secondary of the transformer is typically 1000 turns
of #40 wire wound through the toroid. The primary is
typically 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 primary
difference current divided by the primary-to-secondary
turns ratio is the current that flows through the
secondary wire of the transformer.
1
) can be used which reduces the maximum power
1
FAULT
then enables the external SCR, which
1
signal independent from the phase of
& C
2
FB
1
), and the SCR driver.
) non-inverting input (AC ground
1
). The R
1
and disables Q
1
& C
pulse, the SCR driver enables
TH
2
1
) and, when the AmpOut
SET
threshold voltage, the
timer. If the window
resistor converts the
1
. The current
REF
for the
1
),
1
5
Calculation of R
The
comparator’s V
delay timer and calculated by:
V
R
In practice, the transformer is non-ideal, so R
need to be adjusted by up to 30% to obtain the desired
I
Calculation of V
Since the sense coil is directly connected to the
feedback of the sense amplifier, the V
introduces an I
calculated as follows:
%Error=100 x (V
fault
TH
SET
where:
V
I
t
P
N
R
where:
V
R
R
RL
RL
V
%Error=
FAULT
=I
TH
SET
OS
TH
SET
IN
trip threshold.
= (V
DC
AC
FAULT
AmpOut
= 3.5V
= 5mA (UL943B)
= 1ms (timer delay)
= Period of the AC Line (1/60Hz)
= Ratio of secondary to primary turns (1000:1)
= 505KΩ (511KΩ standard 1% value)
TH
=
= 511KΩ
= 470Ω (typical value)
= 75Ω (sense coil secondary DC resistance)
=
= 3.5V
x 1.41 x R
x N) / (1.41 x I
+/-450µV (worst case)
+/-150µV (typical)
1.5 KΩ (AC
L= 4H, f= 60Hz)
+/- 3.2% (worst case)
+/- 1.1% (typical)
TH
OS
fault
signal
x R
threshold voltage for longer than the
threshold error. This error can be
OS
SET
SET
SET
(j ω L)
Trip Threshold Error
) / (R
x C
Resistor
must
FAULT
impedance of sense coil),
OS
IN
(2
+ RL
x C
π
exceed
x (t/2P)) / N
OS
DC
(
π
+ RL
x t/P))
AC
the
www.fairchildsemi.com
) / V
OS
SET
TH
window
offset
may
(1)
(2)
(3)