U211B2/ B3
95 10272
The converter is based on the charge pumping principle.
With each negative half wave of the input signal, a
V
C3
quantity of charge determined by C is internally
5
V
amplified and then integrated by C at the converter
12
6
output on Pin 10. The conversion constant is determined
by C , its charge transfer voltage of V , R (Pin 10) and
5
ch
6
the internally adjusted charge transfer gain.
I10
Gi
8.3
I9
k = G
V
0
C
5
R
6
V
ch
i
t
The analog output voltage is given by
V = k
t
1
t
3
f
O
t
2
t
tot
The values of C and C must be such that for the highest
5
6
possible input frequency, the maximum output voltage
V does not exceed 6 V. While C is charging up, the R
i
Figure 4. Soft-start
O
5
on Pin 9 is .approx. 6.7 k . To obtain good linearity of the
f/V converter the time constant resulting from R and C
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
t
= build-up of supply voltage
= charging of C to starting voltage
1
i
5
t
2
3
t + t = dead time
1
2
t
t
= run-up time
= total start-up time to required speed
3
tot
voltage on Pin 10 is dependent on C , C and the internal
5
6
charge amplification.
C is first charged up to the starting voltage V with
3
0
typical 45 A current (t ). By then reducing the charging
2
G
V
C
5
i
ch
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
∆V =
O
C
6
The ripple ∆V can be reduced by using larger values of
C . However, the increasing speed will then also be
reduced.
o
increases as the voltage across C increases giving a
3
6
progressively rising charging function which accelerates
the motor more and more strongly with increasing
rotational speed. The charging function determines the
acceleration up to the set-point. The charging current can
have a maximum value of 55 A.
The value of this capacitor should be chosen to fit the
particular control loop where it is going to be used.
Pulse Blocking
Frequency to Voltage Converter
The output of pulses can be blocked using Pin 18 (standby
operation) and the system reset via the voltage monitor if
≥ –1.25 V. After cycling through the switching point
hysteresis, the output is released when V ≤ –1.5 V
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:
V
18
18
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
capacitor C is discharged via an internal resistance
R = 2 k with each charge transfer process of the f/V
i
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.
n
60
f
p (Hz)
where:
4 (20)
n = revolutions per minute
p = number of pulses per revolution
TELEFUNKEN Semiconductors
Rev. A1, 29-May-96
TEMIC [ TEMIC SEMICONDUCTORS ]
