U209B_07 Datasheet, PDF (5/19 Pages) ATMEL Corporation – Phase Control IC for Tacho Applications

U209B
3. Description
3.1 Mains Supply
The U209B 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
Calculations for Mains Supply” on page 9. The reference voltage source on pin 13 of typically
-8.9 V is derived from the supply voltage and represents the reference level of the control unit.
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~
U209B
1
2
3
4
5
R₁
C₁
3.2 Phase Control
The function of the phase control is largely identical to that of the well known integrated circuit
U2008B. 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 4. The
slope of the ramp is determined by C₂ and its charging current. The charging current can be var-
ied using R₂ on pin 5. The maximum phase angle α_max can also be adjusted by using R₂.
When the potential on pin 6 reaches the nominal value predetermined at pin 11, 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).
The current sensor on pin 1 ensures that, for operation with inductive loads, no pulse is gener-
ated 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 11 can be in the range 0 V to -7 V (reference point pin 2).
If V₁₁ = -7 V, the phase angle is at maximum = α_max, i.e., the current flow angle is at minimum.
The minimum phase angle α_min is when V₁₁ = V_{pin 2}.
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4765C–INDCO–02/07