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OM1682A Schematic ( PDF Datasheet ) - IES

Teilenummer OM1682A
Beschreibung Precision Triac Control Thermostat
Hersteller IES
Logo IES Logo 




Gesamt 24 Seiten
OM1682A Datasheet, Funktion
Draft Data Sheet
INTEGRATED CIRCUIT
2004 Jul 26
OM1682
OM1682A
Pwrewciwsio.Dn atrtiaacSchoenterot4l tUhe.rcmoomstat
INTEGRATED ELECTRONIC SOLUTIONS
1BUTLER DRIVE
HENDON SA 5014
AUSTRALIA
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OM1682A Datasheet, Funktion
Integrated Electronic Solutions, Hendon, South Australia
Precision triac control thermostat
Draft Data Sheet
OM1682 OM1682A
See Figure 3, 0M1682 Power Supply
Circuit. A resistor network taken
between terminal T2 of the Triac (TS)
or the load or AC supply (LS) and
VEE provides the zero-crossing
signals. As the AC signal passes
through zero, comparators provide
control signals Tp (when VTS > VCC)
and Tn (when VTS < VEE) indicating
whether the voltage on TS or LS is
greater or less than VCC or VEE
respectively. A resistor network
ensures that these switching points
correspond to equal positive or
negative thresholds about the AC
zero thus giving a symmetrical
zero-crossing drive to the triac gate.
For a resistive load the zero-crossing
information for the triac gate drive is
obtained from pin LS. In circuits
where the triac and the control circuit
are connected to one side of the AC
supply, LS also provides power and
zero-crossing information while the
triac is off, and no connection is
needed to TS. However for reactive
loads it provides the gate control
signals during the ON period.
Synchronisation is obtained from the
threshold comparators at the levels of
VCC and VEE on the chip.
Adjustment of the switching point, and
hence the firing pulse width and
symmetry about the zero crossing
point is possible by varying the values
of the resistors connected between
TS and the triac T2, the resistor to
VEE, and the resistor to VCC; and LS
to the load, VEE and VCC.
With a resistive load, when the triac
has switched on and an AC signal is
no longer available on T2 of the triac,
the synchronisation information, and
the power supply are derived via pin
LS from either the load, or from the
AC supply (depending on the circuit
configuration used). The series
resistor to the load (or AC supply),
together with resistors from pin LS to
VEE and to VCC, are chosen to be
suitable values to generate the triac
gate pulse about the zero-crossing
point to ensure reliable firing of the
triac.
In the circuit configuration in which
the signal for LS is derived from
across the load, there will be no AC
signal until the triac has fired.
Therefore, while the triac is OFF,
synchronising information and the DC
power supply is derived from the AC
signal that is then present across the
triac via pin TS.
6.5 PWR - Power supply boost
An AC signal applied to this terminal
provides additional DC power supply
current using on-chip rectifiers. This is
usually provided via an additional
resistor connected from the PWR pin
to the AC supply. See Figure 3,
OM1682 Power Supply Circuit.
If the OM1682 is able to operate with
narrow gate drive pulses, and only
requires a small average DC supply
current, then there may be sufficient
power available from the
synchronising drive resistors to LS
and TS. However large magnitude
triac trigger pulses or extended pulse
widths to reach triac latching current
levels with light loads may require
additional power sourcing via this
terminal. This will be especially so
with reactive loads, with resistive
loads drawing low currents (less than
400 VA), or with triacs specified for
low gate trigger current sensitivity. No
synchronising signals are derived
from the PWR terminal.
6.6 TRG - Triac gate drive
The triac gate output drives the gate
through a current setting resistor. It
has in-built protection to withstand
transient voltage signals which may
be induced on the gate of the triac by
mains transients during firing. The
gate drive current should be set to a
value suited to the gate sensitivity of
the triac used. The firing pulse width
will need to be of such a width that the
specified latching current of the triac
when used with the design load has
been reached before the gate pulse
ends. The average current this
requires may preclude the powering
of the circuit during the ON cycle from
the LS pin supply alone (to achieve
the required gate pulse width), and an
additional DC boost may be needed
from the PWR terminal.
With a resistive load the triac is fired
at all times with a signal applied to the
gate during the zero-crossing of the
mains. However, with an reactive load
the current is no longer in phase with
the supply voltage across the load;
and there is no signal available to
indicate that the current is
approaching zero at the end of each
conducting half-cycle. When the
current fails below the triac holding
current, the triac switches off, and the
supply voltage at that time appears
across the triac. When configured to
fire reactive loads, the OM1682
detects the presence of this voltage
by the signal on pin TS when the triac
turns off, and acts to re-apply the gate
signal until the signal on TS falls,
indicating that the triac has fired. The
gate drive is held on for short delay
time after the voltage on T2 fails to
ensure the triac current has reached
its latching point.
With an reactive load there is a
transient voltage present on the triac
T2 during the conduction period, and
radio frequency interference (RFI)
suppression and suitable snubbing
measures may be needed.
2004 Jul 26
6

6 Page









OM1682A pdf, datenblatt
Integrated Electronic Solutions, Hendon, South Australia
Precision triac control thermostat
Draft Data Sheet
OM1682 OM1682A
SYMBOL
PARAMETER
CONDITIONS
ICAPoffset
Offset current (as a % of ISA or ISB, where
ICAPoffset = (ICAP/ISA) x 100%, measured at
ISA = ISB = +100 µA dc)
Timing capacitor
ICAP/(ISAISB) Charge current ratio
OM1682A control functions
ISA = ISB = +100 µA
ILOT(low
ILOT(high)
ILIN(low
ILIN(high)
VLIN(threshold)
logical output pull down current
logical output high leakage
logical input current (low)
logical input current (high)
logical input voltage threshold
VLOT = VEE +0.5 V
VLOT = VCC
VLIN = VEE
VLIN = VCC
with respect to VEE
MIN
2.2
TYP
0
MAX
+2.2
UNIT
%
0.9
50 − − µA
− − 1 µA
3 − µA
− − 1 µA
0.8 1.2 1.6 V
10 APPLICATION INFORMATION
10.1 Design considerations
Resistors connected directly to the
AC supply rail should be specified to
withstand the voltage. It is
recommended that Philips
Components VR37 (or VR25)
high-ohmic / high-voltage resistors be
used. These resistors meet the safety
requirements of a number of
international standards on high
voltage applications.
These circuits are designed to
demonstrate the flexibility of
applications using the OM1682 and
OM1682A. No attempt has been
made to use the minimum number of
components, although there are
opportunities to reduce the
component count by using resistors
for multiple functions. There can be
some interaction with reduced
accuracy, and a good understanding
of the OM1682 and OM1682A is
required to find the most cost efficient
design.
10.2 Circuit configurations
Triac control circuits usually have the
load connected between the mains
supply and T2 of the triac, and the
controller together with triac terminal
T1 are connected to the other side of
the supply. This is the application
circuit in figure 5, OM1682 Application
Diagram: Resistive Heating Load,
referenced to mains. An alternative
circuit in which the T2 of the triac and
the load are both connected to the
supply, is shown in figure 7; here the
controller, and temperature sensor
are connected to the junction of the
load and triac terminal T1. Other
circuit configurations will depend on
whether the load is resistive, and
zero-crossing fired, or is reactive and
must be fired as soon as possible
after the current has fallen to zero and
the triac has switched off (for example
figure 6).
10.3 Power supply requirements
The DC power supply current
available for the operation of the
circuit is derived from the resistors
connected to the TS and LS
terminals, plus boost power if needed
from PWR. On the negative half cycle
of the AC signals applied to these
resistors, the current into the OM1682
charges the 100 µF power supply
capacitor connected between VCC
and VEE.
Apart from the current required by the
chip, the triac gate drive presents the
major DC current requirement of the
circuit. As the gate pulse must be
wide enough for the load current to
reach the triac's specified holding
current, this may be a significant load
on the DC supply (especially with
small resistive and reactive triac
loads). Hence the provision of the
PWR terminal which may be needed
for circuits requiring wider gate drive
pulses.
For moderate supply requirements
without separate power boost it is
recommended that PWR be
connected to LS.
10.4 Gate drive
The 300 gate resistor shown in the
application circuits gives a little over
10 mA gate drive. Thus for the circuit
shown a triac would need to be
specified that is suitable for 10 mA
triggering with negative triggering
signal for both positive and negative
voltage on T2. From the threshold
levels determined from the resistive
networks on LS and TS and the AC
supply, the gate pulse width can be
calculated (assuming a sine wave
supply). The specification of the triac
will indicate the latching current for
switch-on, and knowing the minimum
load with which the circuit is to
operate, then proper design will
ensure that the gate pulse is not
removed before the triac current
reaches this figure.
2004 Jul 26
12

12 Page





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