U2008B Datasheet, PDF (4/10 Pages) TEMIC Semiconductors – Low Cost Current Feedback Phase Control Circuit

U2008B
Current Synchronization, Pin 8
Mains
96 11645
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 as long as
triggering is successful.
* Avoiding 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
from the previous half-wave, which flows from the
opposite polarity to the actual supply voltage.
R₂
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BZX55
C6V2
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U2008B
4
A special feature of the IC is the realization of current
synchronization. The device evaluates the voltage at the
pulse output between the gate and reference electrode of
the triac. This results in saving separate current
synchronization input with specified series resistance.
Voltage Synchronization with Mains Voltage
Compensation, Pin 7
The voltage detector synchronizes the reference ramp
with the mains supply voltage. At the same time, the
mains dependent input current at Pin 7 is shaped and rec-
tified internally. This current activates the automatic
retriggering and at the same time is available at Pin 3 (see
figure 8). By suitable dimensioning, it is possible to attain
the specified compensation effect. Automatic
retriggering and mains voltage compensation are not
activated until |V₇ – ₄| increases to 8 V. Resistance, R_sync.,
defines the width of the zero voltage cross-over pulse,
synchronization current, and hence the mains supply
voltage compensation current. If the mains voltage
compensation and the automatic retriggering are not
v ^{required, both functions can be suppressed by limiting}
|V_{7 – 4}| 7 V (see figure 3).
Figure 3. Suppression of automatic retriggering and mains
voltage compensation
A further feature of the IC is the selection between soft-
start or load-current compensation. Soft-start is possible
by connecting a capacitor between Pin 1 and Pin 4, see
figure 7. In the case of load current compensation, Pin 1
is directly connected with resistance R₆, which is used for
sensing load current.
Load Current Detection, Pin 1
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 an
increase of input current at Pin 1. This current increase
controls the internal current source, whose positive
current values is available at Pin 3 (see figure 9). The
output current generated at Pin 3 contains the difference
from the load-current detection and from the
mains-voltage compensation (see figure 1).
The effective control voltage is the final current at Pin 3
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 avoids a decrease in revolution by increasing
the load as well as the increase of revolution by the
increment of mains supply voltage.
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TELEFUNKEN Semiconductors
Rev. A1, 28-May-96