U211B2 Datasheet, PDF (4/20 Pages) TEMIC Semiconductors – Phase Control Circuit - General Purpose Feedback

U211B2/ B3
V_C3
V₁₂
95 10272
V₀
t
t₁
t₂
t₃
t_tot
Figure 4. Soft-start
t₁ = build-up of supply voltage
t₂ = charging of C₃ to starting voltage
t₁ + t₂ = dead time
t₃ = run-up time
t_tot = total start-up time to required speed
C₃ is first charged up to the starting voltage V₀ with
m typical 45 A current (t₂). By then reducing the charging
m current to approx. 4 A, 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 accelerates
the motor more and more strongly with increasing
rotational speed. The charging function determines the
m ^{acceleration up to the set-point. The charging current can}
have a maximum value of 55 A.
Frequency to Voltage Converter
The internal frequency to voltage converter (f/V-
converter) generates a DC signal on Pin 10 which is
proportional to the rotational speed using an AC signal
from a tacho-generator or a light beam whose frequency
is in turn dependent on the rotational speed. The high
impedance input Pin 8, compares the tacho-voltage to a
switch-on threshold of typ. –100 mV. The switch-off
threshold is given with –50 mV. The hysteresis
guarantees very reliable operation even when relatively
simple tacho-generators are used. The tacho-frequency is
given by:
+f
n
60
p (Hz)
where:
n = revolutions per minute
p = number of pulses per revolution
The converter is based on the charge pumping principle.
With each negative half wave of the input signal, a
quantity of charge determined by C₅ is internally
amplified and then integrated by C₆ at the converter
output on Pin 10. The conversion constant is determined
by C₅, its charge transfer voltage of V_ch, R₆ (Pin 10) and
ƪ ƫ + ^{the internally adjusted charge transfer gain.}
G_i
I₁₀
I₉
8.3
k = G_i C₅ R₆ V_ch
The analog output voltage is given by
@ V_O = k f
The values of C₅ and C₆ must be such that for the highest
possible input frequency, the maximum output voltage
W ^{VO does not exceed 6 V. While C5 is charging up, the Ri}
on Pin 9 is .approx. 6.7 k . To obtain good linearity of the
f/V converter the time constant resulting from R_i and C₅
should be considerably less (1/5) than the time span of the
negative half-cycle for the highest possible input
frequency. The amount of remaining ripple on the output
voltage on Pin 10 is dependent on C₅, C₆ and the internal
charge amplification.
G_i V_ch C₅
∆V_O =
C₆
The ripple ∆V_o can be reduced by using larger values of
C₆. However, the increasing speed will then also be
reduced.
The value of this capacitor should be chosen to fit the
particular control loop where it is going to be used.
Pulse Blocking
The output of pulses can be blocked using Pin 18 (standby
operation) and the system reset via the voltage monitor if
V₁₈ ≥ –1.25 V. After cycling through the switching point
hysteresis, the output is released when V₁₈ ≤ –1.5 V
followed by a soft-start such as that after turn on.
Monitoring of the rotation can be carried out by
connecting an RC network to Pin 18. In the event of a
short or open circuit, the triac triggering pulses are cut off
by the time delay which is determined by R and C. The
W ^{capacitor C is discharged via an internal resistance}
R_i = 2 k with each charge transfer process of the f/V
converter. If there are no more charge transfer processes
C is charged up via R until the switch-off threshold is
exceeded and the triac triggering pulses are cut off. For
operation without trigger pulse blocking or monitoring of
the rotation, Pins 18 and 16 must be connected together.
4 (20)
TELEFUNKEN Semiconductors
Rev. A1, 29-May-96