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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)

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U2008B
Current Synchronization, Pin 8
Mains
Current synchronization fulfils two functions:
* Monitoring the current flow after triggering.
In case the triac extinguishes again or it does not switch
on, automatic triggering is activated as long as
triggering is successful.
* Avoiding triggering due to inductive load.
In the case of inductive load operation, the current
synchronization ensures that in the new half wave no
pulse is enabled as long as there is a current available
from the previous half wave, which flows from the
opposite polarity to the actual supply voltage.
R2
2x
BZX55
C6V2
7
U2008B
4
A special feature of the IC is the realization of current
synchronization. The device evaluates the voltage at the
pulse output between the gate and reference electrode of
the triac. This results in saving separate current
synchronization input with specified series resistance.
Voltage Synchronization with Mains Voltage
Compensation, Pin 7
The voltage detector synchronizes the reference ramp
with the mains supply voltage. At the same time, the
mains-dependent input current at Pin 7 is shaped and rec-
tified internally. This current activates the automatic
retriggering and at the same time is available at Pin 3 (see
figure 9). By suitable dimensioning, it is possible to attain
the specified compensation effect. Automatic
retriggering and mains voltage compensation are not
activated until |V7 4| increases to 8 V. The resistance
Rsync. defines the width of the zero voltage cross-over
pulse, synchronization current, and hence the mains sup-
ply voltage compensation current. If the mains voltage
compensation and the automatic retriggering are not
required, both functions can be suppressed by limiting
|V7 – 4| v 7 V (see figure 4).
Figure 4. Suppression of automatic retriggering and mains
voltage compensation
A further feature of the IC is the selection between soft-
start or load-current compensation. Soft start is possible
by connecting a capacitor between Pin 1 and Pin 4, see
figure 8. In the case of load-current compensation, Pin 1
is directly connected with resistance R6, which is used for
sensing load current.
Load Current Detection, Pin 1
The circuit continuously measures the load current as a
voltage drop at resistance R6. The evaluation and use of
both half waves results in a quick reaction to load-current
change. Due to voltage at resistance R6, there is an
increase of input current at Pin 1. This current increase
controls the internal current source, whose positive
current values is available at Pin 3 (see figure 11). The
output current generated at Pin 3 contains the difference
from the load-current detection and from the
mains-voltage compensation (see figure 9).
The effective control voltage is the final current at Pin 3
together with the desired value network. 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 the increase of revolution by the
increment of mains supply voltage.
4 (10)
Rev. A4, 12-Jan-01

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Absolute Maximum Ratings
VS = 14 V, reference point Pin 4, unless otherwise specified
Parameters
Current limitation
Pin 5
t v 10 ms
Sync. currents
t v 10 ms
Pin 7
Phase control
Pin 3
Control voltage
Input current
Charge current
Pin 6
Load current monitoring / Soft start, Pin 1
Input current
Input voltage
Pulse output
Input voltage
Pin 8
Storage temperature range
Junction temperature range
Symbol
–IS
–iS
"IsyncV
"isyncV
–VI
" II
– I ϕmax
II
VI
+VI
–VI
Tstg
Tj
U2008B
Value
30
100
5
20
VS to 0
500
0.5
1
–40 to + 125
2
VS
*40 to )125
*10 to )125
Unit
mA
mA
mA
mA
V
mA
mA
mA
V
V
V
C
C
Thermal Resistance
Junction ambient
Parameters
DIP8
SO8 on p.c.
SO8 on ceramic
Symbol
RthJA
RthJA
RthJA
Value
110
220
140
Unit
K/W
K/W
K/W
Rev. A4, 12-Jan-01
5 (10)