2002 Nov 08
3
Integrated Electronic Solutions, Hendon, South Australia
Data Sheet
General purpose triggering circuit
OM5428
1
FEATURES
Adjustable proportional range
Adjustable hysteresis
Adjustable firing burst repetition time
Adjustable pulse width
Supplied from the mains
Provides supply for external temperature bridge
Low supply current, low dissipation
2
GENERAL DESCRIPTION
The OM5428 is a bipolar integrated circuit delivering
negative pulses for triggering a triac. The flexibility of the
circuit makes it suitable for a variety of applications, such
as:
Synchronous on/off switching
Phase control
Time-proportional control
Temperature control
Motor speed control
3
QUICK REFERENCE DATA
T
amb
= 25
C
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNIT
-
V
EE
DC supply voltage
derived from mains voltage
-
14
-
V
-
I
EE
supply current
quiescent current
-
200
-
A
I
TRIG
output current
set via gate resistor (Rg)
-
-
80
mA
t
w
zero crossing pulse width
sawtooth pulse width
Rz = 500K
RC
(R = 300KW; C = 5nF)
-
-
100
100
-
-
s
s
P
tot
total power dissipation
maximum
-
-
300
mW
T
amb
operating ambient
temperature range
0
-
+125
C
4
ORDERING INFORMATION
TYPE
NUMBER
PACKAGE
NAME
DESCRIPTION
VERSION
OM5428 P
DIP16
plastic dual in-line package; 16 leads (300 mil)
SOT38-1
OM5428 T
SO16
plastic small outline package; 16 leads; body width 3.9 mm
SOT109-1
2002 Nov 08
4
Integrated Electronic Solutions, Hendon, South Australia
Data Sheet
General purpose triggering circuit
OM5428
5
PINNING INFORMATION
5.1
Pinning layout
5.2
Pin description
OM5428
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
PW
XOUT
DIFFEN
QC+
QC
-
IC
-
IC+
SDIS
FLY
SAW
TRIG
RMNS
AMPIN
V
V
EE
XDIS
CC
Fig.1 Pin configuration
SYMBOL
PIN
DESCRIPTION
PW
1
pulse width control input
XOUT
2
zero-crossing detector output
DIFFEN
3
difference amplifier enable output
QC+
4
comparator non-inverting output
IC+
5
comparator non-inverting input
IC
-
6
comparator inverting input
QC
-
7
comparator inverting output
SDIS
8
triac gate sense disable input
AMPIN
9
output stage input
TRIG
10
output stage output
V
EE
11
negative supply
V
CC
12
positive supply
RMNS
13
external power resistor
SAW
14
sawtooth generator trigger input
FLY
15
sawtooth generator output
XDIS
16
zero crossing detector disable input
6
BLOCK DIAGRAM
OM5428
11
13
16
1
12
2
7
3
SUPPLY
ZERO-
CROSSING
DETECTOR
zero-crossing
detector output
enable input
pulse width
control input
negative
supply
external mains
resistor (Rs)
supply
common
5
6
14
8
9
10
15
4
comparator non-
inverting output
comparator
inverting input
comparator non-
inverting input
comparator
inverting output
DIFFERENCE
AMPLIFIER
SAWTOOTH
GENERATOR
OUTPUT
AMPLIFIER
sawtooth
generator
output
output stage
output
output stage
input
sawtooth
generator
input
gate sense
inhibiting input
external
resistor
XDIS
QC
-
QC+
FLY
VCC
RMNS
VEE
PW
XOUT
DIFFEN
IC+
IC
-
SAW
SDIS
AMPIN
TRIG
REGULATOR
v
GATE
SENSE
RESET
pull down on
pin IC-
pull up on
pin IC+
output
amplifier
inhibit
gate
sense
ready from
regulator
cc
pull up
on pin
SAW
output
amplifier
reset
(Rz)
Fig.2 Block diagram of the OM5428
2002 Nov 08
5
Integrated Electronic Solutions, Hendon, South Australia
Data Sheet
General purpose triggering circuit
OM5428
7
FUNCTIONAL DESCRIPTION
Fig.2 shows the functional block
diagram of the OM5428. It comprises
the following sections:
d.c. supply derived from the mains
via a dropping resistor (Rs);
reset to ensure correct startup;
gate sense for reduction in the
number of pulses produced when
firing the triac;
zero-crossing detector for
synchronization of the trigger
pulses;
difference amplifier passing a
signal from a sensor, or indication
of a potentiometer setting or switch
position, etc.;
ramp function generator operating
as the sawtooth oscillator in time
proportional or phase control;
output amplifier amplifying trigger
pulses and driving the triac gate.
7.1
Supply
The OM5428 has been designed so
that it is supplied directly from mains
voltage. For this purpose a regulator
circuit is included to limit the DC
supply voltage. An external resistor
Rs (mains voltage rated) is connected
between the mains active and pin
RMNS; V
CC
is connected to the
neutral line. A smoothing capacitor
C1 is connected between V
CC
and
V
EE
. The circuit produces a negative
supply voltage at V
EE
, which may be
used to supply an external circuit
such as a temperature sensing
bridge.
During the negative half of mains,
current through the external voltage
dropping resistor Rs charges the
external smoothing capacitor C1 to
the shunt voltage of the regulator. The
value of Rs should be chosen such
that it can supply the current for the
OM5428, plus the charge required to
drive the triac gate and any external
(peripheral) circuits connected to V
EE
by recharging the smoothing
capacitor C1 on the mains negative
half cycles. Any excess current is
bypassed through the shunt transistor
of the regulator. The maximum rated
current must not be exceeded.
During the positive half of the mains
cycle the external smoothing
capacitor C1 supplies the circuit. Its
capacitance must be large enough to
maintain the supply voltage above the
minimum specified limit.
A suitable VDR may be connected
across the mains to provide
protection for the OM5428 and the
triac against mains-born transients.
7.2
Reset
A reset circuit providing four reset
functions throughout the OM5428 has
been included.
Initially the reset signal ensures that
trigger pulses are not produced until
V
EE
has reached its minimum value
and C1 is fully charged. The input
SAW (pin14) to the sawtooth
generator is also held at a low state
until the reset threshold has been
reached.
During start-up the reset is also
responsible for holding the input pins
to the difference amplifier, IC+ (pin 5)
at a high state and IC- (pin 6) at a low
state. As a result, functions such as
soft and hard start while phase firing
can be realised.
7.3
Gate sense
Included in the OM5428 is a function
that is capable of determining the
state of the triac. Used to inhibit the
output amplifier, the gate sense circuit
ensures that multiple gate pulses are
not produced, hence reducing overall
current consumption.
7.4
Zero-crossing detector
The OM5428 contains a zero-
crossing detector to produce pulses
that coincide with the zero crossings
of the mains voltage to minimise RF
interference and transients on the
mains supply.
If the load to be driven is purely
resistive, the synchronization voltage
is obtained direct from the mains via a
resistor. As a result trigger pulses
start shortly before, and end shortly
after, each zero-crossing of the mains
voltage. In this manner radio
interference is reduced to a minimum.
If the load contains an inductive
component, the synchronization will
be produced by the internal gate
sense circuit rather than the
zero-crossing detector. The trigger
pulse is then produced at the earliest
possible moment, i.e. immediately
following zero-crossing of the
phase-shifted load current.
During phase control the zero-
crossing detector is used to generate
a sawtooth voltage synchronous with
the mains. As soon as the d.c. control
voltage corresponding to a preset
trigger angle is exceeded the output is
pulsed.
The pulse width control input PW
(pin 1) allows adjustment of the pulse
width at output XOUT (pin 2), to the
value required for the triac. This is
done by choosing the value of
external synchronization resistor Rz
between PW and the AC mains. The
pulse width is determined by the
amount of current flowing to or from
pin PW. Any current exceeding 9uA
will result in the output of the
zero-crossing detector being
disabled. The zero-crossing detector
output is also inhibited when the XDIS
input (pin 16) is HIGH, and enabled
when LOW, e.g. connected to V
EE
.
The pulse width can be determined
using the following formula:
P W
2
=
9
6
10
R z
(
)
Vmains pk
(
)
----------------------------------- rad
asin
100
---------------------------------------------------------------
s
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