Current synchronization fulfils two functions:
* Monitoring the current flow after triggering.
In case the triac extinguishes again or it does not switch
on, automatic triggering is activated until the
triggering is successful.
* Avoiding a triggering due to inductive load.
In the case of inductive load operation the current
synchronization ensures that in the new half wave no
pulse is enabled as long as there is a current available
which from the previous half-wave, which flows from
the opposite polarity to the actual supply voltage.
A special feature of the integrated circuit is the
realization of this current synchronization. The device
evaluates the voltage at the pulse output between gate and
reference electrode of the triac. This results in saving
separate current synchronization input with specified
Voltage Synchronization with Mains Voltage
The voltage detector synchronizes the reference ramp
with the mains-supply voltage. At the same time, the
mains dependent input current at Pin 15 is shaped and
rectified internally. This current activates the automatic
retriggering and at the same time is available at Pin 5. By
suitable dimensioning, it is possible to attain the specified
compensation effect. Automatic retriggering and mains
voltage compensation are not activated until |V15 – 10|
increases to 8 V. Resistance, Rsync. defines the width of
the zero voltage cross over pulse, synchronization
current, and hence the mains supply voltage
If the mains voltage compensation and the automatic
vretriggering are not required, both functions can be
suppressed by limiting |V15 – 10| 7 V (figure 3).
Load Current Compensation
The circuit continuously measures the load current as a
voltage drop at resistance R6. The evaluation and use of
both half waves results in a quick reaction to load current
change. Due to voltage at resistance R6, there is a
difference between both input currents at Pins 1 and 2.
This difference controls the internal current source,
whose positive current values are available at Pins 5
and 6. The output current generated at Pin 5 contains the
difference from the load-current detection and from the
mains-voltage compensation (see figure 1).
The effective control voltage at Pin 4 is the final current
at Pin 5 together with the desired value network. An
increase of mains voltage causes the increase of control
angle α, an increase of load current results in a decrease
in the control angle. This avoiding a decrease in
revolution by increasing the load as well as the increase
of revolution by the increment of mains supply voltage.
Load Current Limitation
The total output load current is available at Pin 6. It
results in a voltage drop across R11. When the potential
of the load current reaches about 70% of the threshold
value (VT70) i.e., ca. 4.35 V at Pin 6, it switches the high
load comparator and opens the switch between Pins 11
and 12. By using an LED between these pins, (11 and 12)
a high load indication can be realized.
If the potential at Pin 6 increases to ca. 6.2 V (= VT100),
it switches the overload comparator. The result is
programmable at Pin 9 (operation mode).
a) αmax (V9 = 0)
In this mode of operation, after V6 has reached the
threshold VT100, Pin 13 switches to –VS (Pin 11) and
Pin 6 to GND (Pin 10). A soft-start capacitor is then
shorted and the control angle is switched to αmax.
This position is maintained until the supply voltage
is switched off. The motor can be started again with
soft-start function when the power is switched on
again. As the overload condition switches Pin 13 to
Pin 11, it is possible to set in a smaller control angle,
αmax, by connecting a further resistance between
Pins 13 and 14.
Rev. A1, 28-May-96