The U209B is designed with voltage limiting and can
therefore be supplied directly from the mains. The supply
voltage between Pin 2 (+ pol/ă) and Pin 3 builds up
across D1 and R1 and is smoothed by C1. The value of the
series resistance can be approximated using (Figure 2):
VM – Vs
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 13 of typ. –8.9 V is
derived from the supply voltage and represents the refer-
ence level of the control unit.
Operation using an externally stabilised DC voltage is not
If the supply cannot be taken directly from the mains
because the power dissipation in R1 would be too large,
then the circuit shown in the following Figure 3 should be
Figure 3. Supply voltage for high current requirements
The function of the phase control is largely identical to
that of the well known integrated circuit U211B. The
phase angle of the trigger pulse is derived by comparing
the ramp voltage, which is mains synchronised by the
voltage detector, with the set value on the control input
Pin 4. The slope of the ramp is determined by C2 and its
charging current. The charging current can be varied
using R2 on Pin 5. The maximum phase angle amax can
also be adjusted using R2.
When the potential on Pin 6 reaches the nominal value
predetermined at Pin 11, then a trigger pulse is generated
whose width tp is determined by the value of C2 (the value
of C2 and hence the pulse width can be evaluated by
assuming 8 ms/nF.
The current sensor on Pin 1 ensures that, for operation
with inductive loads, no pulse will be generated in a new
half cycle as long as 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 11 can be in the range 0 V to
–7 V (reference point Pin 2).
If V11 = –7 V then the phase angle is at maximum = amax
i. e. the current flow angle is a minimum. The minimum
phase angle amin is when V11 = Vpin2.
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, 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 behaviour each
time the supply voltage is switched on or after short
interruptions of the mains supply.
As soon as the supply voltage builds up (t1), 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 11. This behaviour guarantees a gentle start–up for
the motor and automatically ensures the optimum run–up
C3 is first charged up to the starting voltage Vo with
typically 30 mA current (t2). By then reducing the
charging current to approx. 4 mA, the slope of the charging
function is substantially reduced so that the rotational
speed of the motor only slowly increases. The charging
current then increases as the voltage across C3 increases
giving a progressively rising charging function which
more and more strongly accelerates the motor with
increasing rotational speed. The charging function
determines the acceleration up to the set–point. The
charging current can have a maximum value of 50 mA.
Rev. A1: 31.09.1995