U211B2/ B3
Description
Mains Supply
The U211B2 is fitted 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 D
1
and R
1
and is smoothed by C
1
. The value of the
series resistance can be approximated using (see
figure 2):
R
1
When the potential on Pin 7 reaches the nominal value
predetermined at Pin 12, then a trigger pulse is generated
whose width t
p
is determined by the value of C
2
(the value
of C
2
and hence the pulse width can be evaluated by
assuming 8
m
s/nF). At the same time, a latch is set, so that
as long as the automatic retriggering has not been
activated, then no more pulses can be generated in that
half cycle.
The current sensor on Pin 1 ensures that, for operations
with inductive loads, no pulse will be generated 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 12 can be in the range 0 V to
–7 V (reference point Pin 2).
If V
12 =
–7 V then the phase angle is at maximum
=
a
max
i.e., the current flow angle is a minimum. The phase angle
a
min
is minimum when V
12
= V
2
.
+
V 2 –I V
M
S
S
Further information regarding the design of the mains
supply can be found in the data sheets in the appendix.
The reference voltage source on Pin 16 of typ. –8.9 V is
derived from the supply voltage and is used for
regulation.
Operation using an externally stabilised DC voltage is not
recommended.
If the supply cannot be taken directly from the mains
because the power dissipation in R
1
would be too large,
then the circuit shown in the following figure 3 should be
used.
~
Voltage Monitoring
24 V~
1
2
3
4
5
R
1
C
1
95 10362
As the voltage is built up, uncontrolled output pulses are
avoided by internal voltage surveillance. At the same
time, all of the latches in the circuit (phase control, load
limit regulation, soft start) are reset and the soft-start
capacitor is short circuited. Used with a switching
hysteresis of 300 mV, this system guarantees defined
start-up behavior each time the supply voltage is switched
on or after short interruptions of the mains supply.
Figure 3. Supply voltage for high current requirements
Phase Control
There is a general explanation in the data sheet,
TEA1007, on the common phase control function. 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 12. The slope of the ramp is determined by C
2
and its
charging current. The charging current can be varied
using R
2
on Pin 6. The maximum phase angle
a
max
can
also be adjusted using R
2
.
Soft-Start
As soon as the supply voltage builds up (t
1
), the integrated
soft-start is initiated. The figure below shows the
behaviour of the voltage across the soft-start capacitor
and is identical with the voltage on the phase control input
on Pin 12. This behaviour guarantees a gentle start-up for
the motor and automatically ensures the optimum run-up
time.
TELEFUNKEN Semiconductors
Rev. A1, 29-May-96
3 (20)
TEMIC [ TEMIC SEMICONDUCTORS ]
