CA3059 Intersil, CA3059 Datasheet - Page 11

• Manufacturer Part Number: CA3059
• Description: ZERO VOLTAGE CROSSING SWITCH
• Manufacturer: Intersil

Specifications of CA3059

• Rohs Status: RoHS non-compliant

Operation with Low Impedance Sensors
Although the zero-voltage switch can operate satisfactorily with
a wide range of sensors, sensitivity is reduced when sensors
with impedances greater than 20,000 are used. Typical sensi-
tivity is one percent for a 5000 sensor and increases to three
percent for a 0.1M sensor.
Low impedance sensors present a different problem. The sensor
bridge is connected across the internal power supply and causes
a current drain. A 5000 sensor with its associated 5000 series
resistor draws less than 1mA. On the other hand, a 300 sensor
draws a current of 8 to 10mA from the power supply.
Figure 21 shows the 600
redrawn power supply regulation curve for the zero-voltage
switch. When a 10,000
across the circuit is less than 3V and both sensitivity and output
current are significantly reduced. When a 5000 series resistor
is used, the supply voltage is nearly 5V, and operation is
approximately normal. For more consistent operation, however,
a 4000 series resistor is recommended.
Although positive temperature coefficient (PTC) sensors rated at
5k are available, the existing sensors in ovens are usually of a
much lower value. The circuit shown in Figure 22 is offered to
accommodate these inexpensive metal wound sensors. A sche-
matic diagram of the CA3080 integrated circuit operation
transconductance amplifier used in Figure 22, is shown in Figure
23. With an amplifier bias current, I
transconductance of 2m is achieved in this configuration. The
CA3080 switches when the voltage at terminal 2 exceeds the
voltage at terminal 3. This action allows the sink current, I
flow from terminal 13 of the zero-voltage switch (the input imped-
ance to terminal 13 of the zero-voltage switch is approximately
50k ); gate pulses are no longer applied to the triac because Q
of the zero-voltage switch is on. Hence, if the PTC sensor is cold,
i.e., in the low resistance state, the load is energized. When the
temperature of the PTC sensor increases to the desired temper-
ature, the sensor enters the high resistance state, the voltage on
FIGURE 21. POWER SUPPLY REGULATION OF THE CA3059
10
8
6
4
2
0
GATE PULSES: A. SCHEMATIC DIAGRAM; B.
PEAK GATE CURRENT (FAT TERMINAL 3) AS A
FUNCTION OF GATE VOLTAGE
WITH A 300
VALUES OF SERIES RESISTOR.
0
600 LOAD LINE
2
R
SUPPLY VOLTAGE (V)
S
= 10K
series resistor is used, the voltage
R
SENSOR (600
S
load line of a 300
= 5K
4
ABC
6
, of 100 A, a forward
LOAD) FOR TWO
Application Note 6182
8
sensor on a
S
, to
2
11
terminal 2 becomes greater than that on terminal 3, and the triac
switches the load off.
Further cycling depends on the voltage across the sensor.
Hence, very low values of sensor and potentiometer resis-
tance can be used in conjunction with the zero-voltage
switch power supply without causing adverse loading effects
and impairing system performance.
Interfacing Techniques
Figure 24 shows a system diagram that illustrates the role of
the zero-voltage switch and thyristor as an interface between
the logic circuitry and the load. There are several basic inter-
facing techniques. Figure 25A. shows the direct input tech-
nique. When the logic output transistor is switched from the
on state (saturated) to the off state, the load will be turned on
at the next zero-voltage crossing by means of the interfacing
zero-voltage switch and the triac. When the logic output tran-
sistor is switched back to the on state, zero crossing pulses
from the zero-voltage switch to the triac gate will immediately
cease. Therefore, the load will be turned off when the triac
commutates off as the sine wave load current goes through
zero. In this manner, both the turn-on and turn-off conditions
INVERTING
INVERTING
AMPLIFIER
FIGURE 22. SCHEMATIC DIAGRAM OF CIRCUIT FOR USE
IAS INPUT
1mA
PTC
INPUT
INPUT
NON-
FIGURE 23. SCHEMATIC DIAGRAM OF THE CA3080
2
3
5
WITH LOW RESISTANCE SENSOR
Q
4
Q
100 A
3
D
2
0.01 F
1
1
D
2
Q
Q
CA3080
270
3
2
7
5
4
Q
5
IN914
IN914
IABC
100 A
6
Q
0.01
6
D
F
3
Q
7
13
2
8
7
D
4
9
Q
ZVS
3
11
10
Q
8
5
11
D
D
5K
5
6
4
Q
Q
OUTPUT
9
10
V-
V +
7
6
4