U2010B_10 Datasheet, PDF (6/18 Pages) ATMEL Corporation – Programmable Load-current Limitation with Over- and High-load Output

3.7 Load-current Compensation
The circuit continuously measures the load current as a voltage drop at resistance R₆. The eval-
uation and use of both half waves results in a quick reaction to load-current change. Due to the
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 1-2 on page 2.
The efficient impedance of the set-point network generates a voltage at pin 4. A current, flowing
out of pin 5 through R₁₀, modulates this voltage. 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 an increase of revolution
by the increment of the mains supply voltage.
3.8 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 (V_T70), i.e., about 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 about 6.2 V (= V_T100), it switches the overload comparator.
The result is programmable at pin 9 (operation mode).
3.8.1
Mode Selection
a)
b)
c)
α_max (V₉ = 0)
In this mode of operation, pin 13 switches to -V_S (pin 11) and pin 6 to GND
(pin 10) after V₆ has reached the threshold V_T100. A soft-start capacitor is then
shorted and the control angle is switched to α_max. This position is maintained
until the supply voltage is switched off. The motor can be started again with the
soft-start function when the power is switched on again. As the overload condition
switches pin 13 to pin 11, it is possible to use a smaller control angle, α_max, by
connecting a further resistance between pins 13 and 14.
Auto start (pin 9 – open), see Figure 7-8 on page 12
The circuit behaves as described above, with the exception that pin 6 is not
connected to GND. If the value of V6 decreases to 25% of the threshold
value (V_T25), the circuit becomes active again with soft start.
I_max (V₉ = V₈), see Figure 7-10 on page 13
When V₆ has reached the maximum overload threshold value (i.e., V₆ = V_T100),
pin 13 is switched to pin 8 (V_Ref) through the resistance R (= 2 kΩ) without the
soft-start capacitor discharging at pin 7. With this mode of operation, direct
load-current control (I_max) is possible.
6 U2010B
4766C–INDCO–04/10