U211B Datasheet, PDF (4/30 Pages) ATMEL Corporation – Phase Control IC with Overload Limitation for Tacho Applications

3. Mains Supply
The U211B is equipped with voltage limiting and can therefore be supplied directly from the
mains. The supply voltage between pin 2 (+ pol/_|_) and pin 3 builds up across D₁ and R₁ and is
smoothed by C₁. The value of the series resistance can be approximated using:
R₁
=
V_{-----M-----–-----}V_----S--
2 I_S
Further information regarding the design of the mains supply can be found in the section “Design
Hints” on page 9. The reference voltage source on pin 16 of typically -8.9 V is derived from the
supply voltage and is used for regulation.
Operation using an externally stabilized DC voltage is not recommended.
If the supply cannot be taken directly from the mains because the power dissipation in R₁ would
be too large, the circuit as shown in Figure 3-1 should be used.
Figure 3-1. Supply Voltage for High Current Requirements
~
24 V~
1
2
3
4
5
R1
C1
4. Phase Control
The phase angle of the trigger pulse is derived by comparing the ramp voltage (which is mains
synchronized by the voltage detector) with the set value on the control input pin 12. The slope of
the ramp is determined by C₂ and its charging current. The charging current can be varied using
R₂ on pin 6. The maximum phase angle α_max can also be adjusted by using R₂.
When the potential on pin 7 reaches the nominal value predetermined at pin 12, a trigger pulse
is generated whose width t_p is determined by the value of C₂ (the value of C₂ and hence the
pulse width can be evaluated by assuming 8 µs/nF). At the same time, a latch is set, so that as
long as the automatic retriggering has not been activated, no more pulses can be generated in
that half cycle.
The current sensor on pin 1 ensures that, for operations with inductive loads, no pulse will be
generated in a new half cycle as long as a current from the previous half cycle is still flowing in
the opposite direction to the supply voltage at that instant. This makes sure that “gaps” in the
load current are prevented.
The control signal on pin 12 can be in the range of 0 V to -7 V (reference point pin 2).
If V₁₂ = -7 V, the phase angle is at maximum (α_max), i.e., the current flow angle, is at minimum.
The phase angle is minimum (α_min) when V₁₂ = V₂.
4 U211B
4752B–INDCO–09/05