The output stage logic now brings V14 to low potential
and closes the switching output Pin 10. This has the effect
of discharging C1 via R9 and the switch S1 until the
approximately 300 mV hysteresis of the comparator is
completed. The discharge time is dependent on the
control voltage V8.
Comp. 1 then switches over again and the cycle begins
once more (see figure 3). This two-state controller
compensates the influence of the mains voltage, with the
result that the motor voltage or motor speed is largely
determined by the magnitude of the control voltage.
Current Control, Pin 11
If the current flowing through the IGBT (or MOSFET)
and the shunt resistor R8 becomes so high that a voltage
higher than 1.5 V arises at Pin 11, a second control loop
formed with the comparator Comp. 2 becomes active,
and overrides the first control loop via an AND gate. This
causes the average value of the current, fed to the motor,
to be controlled to a constant value. This in turn results in
a speed which decreases greatly with the increasing
torque (see figure 4).
Figure 3. Pulse width control signal characteristics
Figure 4. Influence of current control on the characteristic
(curve) of a motor
By exceeding the maximum current which is adjustable
with R8, the control dependent voltage V8 (shunt
characteristic) reaches the dotted lines (series
characteristic). By applying a current which depends on
the load voltage across R6, the constant value of the
current can be further influenced. In addition, the current
control limits the starting current.
In the case of effective current limiting, alteration of the
rectified mains voltage has an effect on the power taken
up. In order to compensate for this influence, the resistor
R7 is connected to Pin 11. If dimensioned appropriately,
the consumed power is independent of changes in the
mains voltage within a wide range of this voltage.
Operation Mode Selection, Pin 5
It is possible to program three modes of operation with the
tristate input, as follows:
a) Intermittent operation (Pin 5 connected to +VS)
A signal emitted by an internal oscillator (see
figure 5) switches the output stage ON and OFF
periodically via S2. This intermittent operation is
very suitable for certain uses.
b) Stop function (Pin 5 open)
The output is continuously switched off, the motor is
c) Normal function (Pin 5 connected to V12)
The motor runs continuously.
Temperature Monitoring, Pin 4
The circuit also has a monitoring input. If a NTC-resistor
is connected to this input, for example, it functions as a
temperature sensor. If the voltage V4 falls below the first
threshold VT80 (approximately 420 mV) as a result of the
increasing temperature, an external LED D3, which is
connected between Pin 1 and Pin 2, starts to blink. If the
temperature increases further and the voltage V4 falls
below a second threshold VT100 (approximately
350 mV), a latch is set. The latch makes this LED light up
continuously, the output stage is blocked. The motor is
switched-OFF and remains switched-OFF until the
temperature has fallen and until the mains voltage is
switched-OFF and switched-ON again (the latch is solely
reset by the voltage monitoring). A second LED D2,
which is connected between Pin 2 and Pin 16 and which
is continuously illuminated (switch-ON) during normal
operation, is switched-OFF.
In the event of wire breakage in the sensor branch, Pin 4
is pulled up to +VS. After the switch-OFF threshold
VTOFF (approximately VS–1.8 V) has been exceeded, the
circuit ensures that the latch is set here too. This
guarantees safe operation.
4 (9) TELEFUNKEN Semiconductors
Rev. A1, 29-May-96