U2008B Datasheet, PDF (3/10 Pages) TEMIC Semiconductors – Low Cost Current Feedback Phase Control Circuit

Pin Description
I_{sense 1}
Cϕ ₂
Control ₃
GND ₄
8 ^Output
7 ^Vsync.
6 ^Rϕ
* ₅
V_S
95 11405
U2008B
Pin Symbol
Function
1
I_sense Load current sensing
2
Cϕ Ramp voltage
3 Control Control input / compensation
output
4
GND Ground
5
–V_S Supply voltage
6
Rϕ Ramp current adjustment
7
V_sync. Voltage synchronization
8
Output Trigger output
Mains Supply, Pin 5, Figure 2
The integrated circuit U2008B, which also contains
voltage limiting, can be connected via D₁ and R₁ via the
* ă mains supply. Supply voltage between Pin 4 (pos._, )
* and Pin 5 is smoothed by C₁.
Series resistance R₁ can be calculated as follows:
+ R_1max
0.85
x
V_M – V_Smax
2 x I_tot
whereas
V_M
V_Smax
I_tot
+ Mains voltage
+ Maximum supply voltage
+ ) I_Smax I_x = Total current compensation
The appendix provides further information regarding the
design (see figures 10, 11 and 12). An operation with
external stabilized DC voltage is not recommended.
Voltage Monitoring
As the voltage is built up, uncontrolled output pulses are
avoided by internal voltage monitoring. Apart from that
all the latches in the circuit (phase control, load limit
regulation) are reset and the soft-start capacitor is short
circuited. This guarantees a specified start-up behavior
each time the supply voltage is switched on or after short
interruptions of the mains supply. Soft-start is initiated
after the supply voltage has been built up. This behavior
guarantees a gentle start-up for the motor and
automatically ensures the optimum run-up time.
Phase Control, Pin 6
The function of the phase control is largely identical to the
well known IC family TEA1007. The phase angle of the
trigger pulse is derived by comparing the ramp voltage V₂
at Pin 2 with the set value on the control input, Pin 3. The
slope of the ramp is determined by C₃ and its charging
current I _ö.
The charging current can be regulated, changed, altered
using R₈ at Pin 6. The maximum phase angle, α_max,
(minimum current flow angle ö_min) can also be adjusted
by using R₈ (see figure 4).
When the potential on Pin 2 reaches the set point level of
Pin 3, a trigger pulse is generated whose pulse width, t_p,
is determined from the value of C₃ (t_p = 9 ms/nF, see
figure 6). At the same time, a latch is set with the output
pulse, as long as the automatic retriggering has not been
activated, then no more pulses can be generated in that
half cycle. Control input at Pin 3 (with respect to Pin 4)
has an active range from –9 V to –1 V. When V₃ = –9 V,
then the phase angle is at its maximum α_max i.e., the
w ^{current flow angle is minimum. The minimum phase}
angle α_min is set with V₃ –1 V.
Automatic Retriggering
The current-detector circuit monitors the state of the triac
after triggering by measuring the voltage drop at the triac
gate. A current flow through the triac is recognized, when
the voltage drop exceeds a threshold level of typ. 40 mV.
If the triac is quenched within the relevant half-wave after
triggering; for example owing to low load currents before
or after the zero crossing of current wave or; for commu-
tator motors, owing to brush lifters. Then the automatic
retriggering circuit ensures immediate retriggering, if
necessary with a high repetition rate, t_pp/t_p, until the triac
remains reliably triggered.
TELEFUNKEN Semiconductors
Rev. A1, 28-May-96
3 (10)