U211B ATMEL Corporation, U211B Datasheet - Page 4

• Manufacturer Part Number: U211B
• Description: as U209B + Foldback
• Manufacturer: ATMEL Corporation

Description
Mains Supply
The U211B 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
series resistance can be approximated using:
Further information regarding the design of the mains
supply can be found in the design hints. 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 stabilized DC voltage is not
recommended.
If the supply cannot be taken directly from the mains
because the power dissipation in R
then the circuit shown in figure 5 should be used.
Phase Control
The phase angle of the trigger pulse is derived by compar-
ing 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
charging current. The charging current can be varied
using R
also be adjusted using R
U211B
4 (21)
24 V~
Figure 5. Supply voltage for high current requirements
~
2
1
on Pin 6. The maximum phase angle a
and R
R
1
+
1
and is smoothed by C
V
R
M
1
2 I
1
– V
S
2
S
.
2
C
1
1
3
would be too large,
1
. The value of the
4
2
max
and its
5
can
When the potential on Pin 7 reaches the nominal value
predetermined at Pin 12, then a trigger pulse is generated
whose width t
of C
assuming 8 ms/nF). At the same time, a latch is set, so that
as long as the automatic retriggering has not been
activated, 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
the current flow angle is a minimum. The phase angle
a
Voltage Monitoring
As the voltage is built up, uncontrolled output pulses are
avoided by internal voltage surveillance. At the same
time, all 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.
Soft Start
As soon as the supply voltage builds up (t
soft start is initiated. Figure 6 shows the behaviour of the
voltage across the soft-start capacitor which is identical
with the voltage on the phase-control input on Pin 12.
This behavior guarantees a gentle start-up for the motor
and automatically ensures the optimum run-up time.
min
12 =
2
is minimum when V
and hence the pulse width can be evaluated by
–7 V, the phase angle is at maximum
p
is determined by the value of C
12
= V
2
.
Rev. A4, 03-Aug-01
1
), the integrated
2
=
(the value
a
max,
i.e.,