U2008B_07 Datasheet, PDF (5/13 Pages) ATMEL Corporation – Low-cost Phase-control IC with Soft Start

U2008B
2.6 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 rectified internally. This
current activates automatic retriggering and at the same time is available at Pin 3 (Figure 5-5 on
page 9). By suitable dimensioning, it is possible to attain the specified compensation effect.
Automatic retriggering and mains voltage compensation are not activated until ⏐V₇ - V₄⏐
increases to 8 V. The 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 required, both functions can be
suppressed by limiting ⏐V₇ - V₄⏐ ≤ 7 V (see Figure 2-2).
Figure 2-2. Suppression of Automatic Retriggering and Mains Voltage Compensation
Mains
R₂
2x
BZX55
C6V2
7
U2008B
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A further feature of the IC is the selection between soft start and load-current compensation.
Soft start is possible by connecting a capacitor between Pin 1 and Pin 4 (Figure 5-4 on page 8).
In the case of load-current compensation, Pin 1 is directly connected with resistance R₆, which is
used for sensing load current.
2.7 Load Current Detection, Pin 1
The circuit continuously measures the load current as a voltage drop at resistor R₆. The evalua-
tion and use of both half waves results in a quick reaction to load-current change. Due to voltage
at resistor R₆, there is an increase of input current at Pin 1. This current increase controls the
internal current source, whose positive current values are available at Pin 3 (see Figure 5-7 on
page 9). The output current generated at Pin 3 contains the difference from the load-current
detection and the mains-voltage compensation (see Figure 5-5 on page 9).
The effective control voltage is the final current at Pin 3 together with the desired value network.
An increase of mains voltage causes an increase of the control angle α. An increase of load cur-
rent results in a decrease of the control angle. This avoids a decrease in revolution by increasing
the load as well as an increase of revolution by the increment of mains supply voltage.
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4712C–AUTO–07/07