CA3059

Manufacturer Part NumberCA3059
DescriptionZERO VOLTAGE CROSSING SWITCH
ManufacturerIntersil
CA3059 datasheet
 


Specifications of CA3059

Rohs StatusRoHS non-compliant  
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anced (by adjustment of R
), the potential at point A will
4
increase when temperature is low since it was assumed that
the sensor has a negative temperature coefficient. The
potential at the noninverting terminal, being greater than that
at the inverting terminal at the amplifier, causes the multivi-
brator to oscillate at approximately 10kHz. The oscillations
are transformer coupled through a current limiting resistor to
the gate of the thyristor, and trigger it into conduction.
When the thyristor conducts, the load receives AC input
power, which tends to increase the temperature of the sen-
sor. This temperature increase decreases the potential at
point A to a value below that at point B and the multivibrator
is disabled, which action, in turn, turns off the thyristor. The
temperature is thus controlled in an of/off fashion.
Capacitor C
is used to provide a low impedance path to
1
ground for feedback induced signals at terminal No. 5 while
blocking the direct current bias provided by resistor R
Resistor R
provides current limiting. Resistor R
2
secondary current of the transformer to prevent excessive
current flow to the control terminal of the CA3094.
Photocoupler Isolation - In Figure 28, a photocoupler pro-
vides electrical isolation of the sensor logic from the
incoming AC power lines. When a logic “1” is applied at the
input of the photocoupler, the triac controlling the load will be
turned on whenever the line voltage passes through zero.
When a logic”0” is applied to the photocoupler, the triac will
turn off and remain off until a logic “1” appears at the input of
the photocoupler.
Temperature Controllers
Figure 29 shows a triac used in an of/off temperature controller
configuration. The triac is turned on at zero-voltage whenever
the voltage V
exceeds the reference voltage V
S
characteristic of this system, shown in Figure 30A., indicates
significant thermal overshoots and undershoots, a well known
characteristic of such a system. The differential or hysteresis of
this system, however, can be further increased, if desired, by
the addition of positive feedback.
10K
2 W
5
6
2
120 VAC
R
14
60Hz
P
+
13
CA3059
100 F
-
15VDC
NTC
8
SENSOR
7
9
10 11
V
S
V
R
FIGURE 29. CA3059 ON/OFF TEMP. CONTROLLER
Application Note 6182
For precise temperature control applications, the proportional
control technique with synchronous switching is employed. The
transfer curve for this type of controller is shown in Figure 30B.
In this case, the duty cycle of the power supplied to the load is
varied with the demand for heat required and the thermal time
constant (inertia) of the system. For example, when the temper-
ature setting is increased in an of/off type of controller, full
power (100 percent duty cycle) is supplied to the system This
effect results in significant temperature excursions because
there is no anticipatory circuit to reduce the power gradually
before the actual set temperature is achieved. However, in a
proportional control technique, less power is supplied to the
load (reduced duty cycle) as the error signal is reduced (sensed
temperature approaches the set temperature).
TEMPERATURE
SETTING
OVER-
SHOOT DIFFERENTIAL
.
1
limits the
3
UNDER-
SHOOT
TIME
FIGURE 30A.
FIGURE 30. TRANSFER CHARACTERISTICS OF A. ON/OFF
AND B. PROPORTIONAL CONTROL SYSTEMS
Before such a system is implemented, a time base is chosen
so that the on time of the triac is varied within this time base.
The ratio of the on-to-off time of the triac within this time
interval depends on the thermal time constant of the system
. The transfer
R
and the selected temperature setting. Figure 31 illustrates
the principle of proportional control. For this operation,
power is supplied to the load until the ramp voltage reaches
a value greater than the DC control signal supplied to the
opposite side of the differential amplifier. The triac then
remains off for the remainder of the time base period. As a
result, power is “proportioned” to the load in a direct relation
to the heat demanded by the system.
R
L
1
3
MT
2
TRIAC
TRIAC
4
MT
G
1
ON
25%
POWER
OUTPUT
12
3
FIGURE 31. PRINCIPLES OF PROPORTIONAL CONTROL
14
TEMPERATURE
SETTING
o
DIFFERENTIAL
2
C
TIME
FIGURE 30B.
RAMP
SIGNAL
LEVEL 1
LEVEL 2
LEVEL 3
OFF
50%
75%
POWER
POWER
OUTPUT
OUTPUT
POWER
TO LOAD
2
1
TIME
o
0.5
C