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U2008B
Rev. A4, 12-Jan-01
1 (10)
Low-Cost Phase-Control IC with Soft Start
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
Automatic
retriggering
Limiting
detector
Current
detector
Full wave load
current detector
Soft start
Voltage
detector
7
Phase
control unit
= f (V
3
)
6
Mains voltage
compensation
Supply
voltage
limiting
Reference
voltage
Voltage
monitoring
2
3
5
4
1
8
R
2
330 k
W
22 k
W/2W
BYT51K
R
1
D
1
R
8
1 M
W
180
W
R
3
TIC
226
Load
100 k
W
R
10
Load current
compensation
C
4
Set point
100 nF
C
3
3.3 nF
R
6
230 V ~
R
14
47 k
W
P
1
R
7
GND
V
S
C
1
25 V
+
^
V
(R6)
=
250 mV
U2008B
a
max
22
mF/
Figure 1. Block diagram with typical circuit: Load current sensing
U2008B
Rev. A4, 12-Jan-01
2 (10)
Ordering Information
Extended Type Number
Package
Remarks
U2008B-x
DIP8
Tube
U2008B-xFP
SO8
Tube
U2008B-xFPG3
SO8
Taped and reeled
Automatic
retriggering
Limiting
detector
Current
detector
Full wave load
current detector
Soft start
Voltage
detector
7
Phase
control unit
= f (V
3
)
6
Mains voltage
compensation
Supply
voltage
limiting
Reference
voltage
Voltage
monitoring
2
3
5
4
1
8
R
2
680 k
W
22 k
W/2W
BYT51K
R
1
D
1
a
max
R
8
470 k
W
180
W
R
3
TIC
226
Load
68 k
W
R
10
C
4
Set point
100 nF
C
3
10 nF
230 V ~
P
1
50 k
W
R
7
220 k
W
GND
V
S
C
1
100
mF/
25 V
+
L
C
5
Soft start
4.7
mF/ 25 V
N
U2008B
Figure 2. Block diagram with typical circuit: Soft start
U2008B
Rev. A4, 12-Jan-01
3 (10)
Pin Description
1
2
3
4
8
7
6
5
I
sense
C
Control
GND
Output
V
sync.
R
*V
S
U2008B
Figure 3. Pinning
Pin
Symbol
Function
1
I
sense
Load current sensing
2
C
Ramp voltage
3
Control
Control input / compensation
output
4
GND
Ground
5
V
S
Supply voltage
6
R
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 D
1
and R
1
via the
mains supply. Supply voltage
* between Pin 4 (pos.
,
)
and Pin 5
* is smoothed by C
1
.
Series resistance R
1
can be calculated as follows:
R
1max
+ 0.85 x
V
M
V
Smax
2 x I
tot
where:
V
M
+ Mains voltage
V
Smax
+ Maximum supply voltage
I
tot
+ I
Smax
)I
x
= Total current compensation
I
Smax
= Maximum current consumption of the IC
I
x
= 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 V
2
at Pin 2 with the set value on the control input, Pin 3. The
slope of the ramp is determined by C
3
and its charging
current I
.
The charging current can be regulated, changed, altered
using R
8
at Pin 6. The maximum phase angle,
max,
(minimum current flow angle
min
) can also be adjusted
by using R
8
(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, t
p
,
is determined from the value of C
3
(t
p
= 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 V
3
= 9 V,
then the phase angle is at its maximum
max,
i.e., the
current flow angle is minimum. The minimum phase
angle
min
is set with V
3
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, t
pp
/t
p
, until the triac
remains reliably triggered.
U2008B
Rev. A4, 12-Jan-01
4 (10)
Current Synchronization, Pin 8
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.
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 |V
7
4
| increases to 8 V. The resistance
R
sync.
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
|V
7 4
|
v 7 V (see figure 4).
R
2
2x
BZX55
C6V2
U2008B
7
4
Mains
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 R
6
, 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 R
6
. The evaluation and use of
both half waves results in a quick reaction to load-current
change. Due to voltage at resistance R
6
, 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
. 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.
U2008B
Rev. A4, 12-Jan-01
5 (10)
Absolute Maximum Ratings
V
S
= 14 V, reference point Pin 4, unless otherwise specified
Parameters
Symbol
Value
Unit
Current limitation
Pin 5
I
S
30
mA
t
v
10 ms
i
S
100
mA
Sync. currents
Pin 7
t
v
10 ms
"
I
syncV
"
i
syncV
5
20
mA
mA
Phase control
Pin 3
Control voltage
V
I
V
S
to 0
V
Input current
"
I
I
500
mA
Charge current
Pin 6
I
max
0.5
mA
Load current monitoring / Soft start, Pin 1
Input current
I
I
1
mA
Input voltage
V
I
40 to + 125
V
Pulse output
Input voltage
Pin 8
+V
I
V
I
2
V
S
V
V
Storage temperature range
T
stg
*40 to )125
C
Junction temperature range
T
j
*10 to )125
C
Thermal Resistance
Parameters
Symbol
Value
Unit
Junction ambient
DIP8
SO8 on p.c.
SO8 on ceramic
R
thJA
R
thJA
R
thJA
110
220
140
K/W
K/W
K/W