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Low-Cost Phase-Control IC with Soft Start
U2008B
Description
The U2008B is designed as a phase-control circuit in
bipolar technology. It enables load-current detection as
well as mains-compensated phase control. Motor control
with load-current feedback and overload protection are
preferred applications.
Features
D Full wave current sensing
D Mains supply variation compensated
D Variable soft-start or load-current sensing
D Voltage and current synchronization
D Automatic retriggering switchable
D Triggering pulse typ. 125 mA
D Internal supply-voltage monitoring
D Current requirement v 3 mA
Applications
D Low-cost motor control
D Domestic appliance
Block Diagram
230 V ~
Load
Limiting
detector
22 kW/2W BYT51K
R2
330 kW
R1 D1
amax
R8
1 MW
76
Voltage
detector
Mains voltage
compensation
Automatic
retriggering
TIC
226
R3
180W
8
1
Current
detector
Full wave load
current detector
Soft start
R6
^
V(R6)
=
±250
mV
Phase
control unit
ö = f (V3)
U2008B
23
C3
3.3 nF
C4
100 nF
+–
Supply
voltage
limiting
Reference
voltage
Voltage
monitoring
R10 100 kW
Load current
compensation
5 –VS
C1
22 mF/
25 V
4 GND
R14
47 kW
Set point
R7
P1
Figure 1. Block diagram with typical circuit: Load current sensing
Rev. A4, 12-Jan-01
1 (10)

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U2008B
Ordering Information
Extended Type Number
U2008B-x
U2008B-xFP
U2008B-xFPG3
Package
DIP8
SO8
SO8
Remarks
Tube
Tube
Taped and reeled
230 V ~
L
Load
Limiting
detector
22 kW/2W
BYT51K
R2
680 kW
R1 D1
amax
R8
470 kW
76
Voltage
detector
Mains voltage
compensation
Automatic
retriggering
U2008B
TIC
226
R3
180W
8
1
Current
detector
Full wave load
current detector
Soft start
C5 Soft start
4.7mF/ 25 V
Phase
control unit
ö = f (V3)
23
C3 C4
10 nF 100 nF
+–
Supply
voltage
limiting
Reference
voltage
Voltage
monitoring
5 –VS
C1
100 mF/
25 V
4 GND
R10 68 kW
Set point
R7
220 kW
P1
50 kW
N
Figure 2. Block diagram with typical circuit: Soft start
2 (10)
Rev. A4, 12-Jan-01

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U2008B
Pin Description
Isense 1
8 Output
Cϕ 2
Control 3
U2008B
7 Vsync.
6 Rϕ
GND 4
5 *VS
Figure 3. Pinning
Pin Symbol
Function
1 Isense Load current sensing
2 Cϕ Ramp voltage
3 Control Control input / compensation
output
4 GND Ground
5 –VS Supply voltage
6 Rϕ Ramp current adjustment
7 Vsync. 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
mains supply. Supply voltage * between Pin 4 (pos., ă)
and Pin 5 * is smoothed by C1.
Series resistance R1 can be calculated as follows:
R1max +
0.85 x
VM – VSmax
2 x Itot
where:
VM
VSmax
Itot
ISmax
Ix
+ Mains voltage
+ Maximum supply voltage
+ ISmax )Ix = Total current compensation
= Maximum current consumption of the IC
= Current consumption of the external
components
An operation with external stabilized DC voltage is not
recommended.
Voltage Monitoring
When the voltage is built up, uncontrolled output pulses
are avoided by internal voltage monitoring. Apart from
that, all 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
that of the well-known IC U211B. 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, αmax,
(minimum current flow angle ömin) can also be adjusted
by using R8 (see figure 5).
When the potential on Pin 2 reaches the set point level of
Pin 3, a trigger pulse is generated whose pulse width, tp,
is determined from the value of C3 (tp = 9 ms/nF, see
figure 7). 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 –2 V. When V3 = –9 V,
then the phase angle is at its maximum αmax, i.e., the
current flow angle is minimum. The minimum phase
angle αmin is set with V3 w –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), the automatic
retriggering circuit ensures immediate retriggering, if
necessary with a high repetition rate, tpp/tp, until the triac
remains reliably triggered.
Rev. A4, 12-Jan-01
3 (10)