
U690B
TELEFUNKEN Semiconductors
Rev. A2, 28-Apr-97
7 (9)
Applications
Frequency Comparator
Speed Depending Switch with Hysteresis,
Figure 5
This circuit can be used to activate a load, such as a
warning lamp or buzzer via the relay (terminal A) at a
certain speed. The speed information is applied to signal
input, Pin 3, e.g. from Hall generator via terminal V.
It is compared in the integrated circuit with a reference
frequency created by the oscillator. The oscillator
frequency, f, is generated with external resistor, R
2
R
7
,
and capacitor, C
2
.
If the frequency at Pin 3 is less than f/64, the relay control
ouput is deactivated.
If the frequency at Pin 3 is greater than f/64, the relay
control output is activated and at the same time the
hysteresis output, Pin 7, is disabled, the frequency is
reduced. This means Pin 7 supplies no current for
charging the capacitor, C
2
; therefore, R
2
and C
2
alone
define the oscillator frequency i.e., f
R
2
C
2
.
The hysteresis frequency is determined with the resistor,
R
7
.
Motor Speed Depending Switch with
Hysteresis, Figure 6
This circuit, figure 6, has the same function as the speed
with hysteresis mentioned above.
Information regarding motor speed (rpm) from the
ignition coil is delivered to signal input, Pin 3, via
terminal 1. Resistor values, R
3
and R
5
are so
dimensioned, that there is a peak voltage of nearly 3 V at
Pin 3 (from the ignition coil). Pin 4 is connected to GND,
so that there is a bypass for debouncing. In this way,
ignition pulse is supplied to frequency comparator.
Relay
R1
C2
1
2
6
5
8
7
3
4
94 8866
U690B
R3
R8
C3
15
C1
R7
R2
A
D2
Z1
V
31
D1
Figure 5. Speed switch
U 690 B
1
2
6
5
8
7
3
4
C1
R5
R3
Relay
D1
R1
R2
R7
C2
94 8867
15
A
1
31
Figure 6. Motor speed switch with hysteresis