CA3059 Intersil, CA3059 Datasheet - Page 20

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

Specifications of CA3059

• Rohs Status: RoHS non-compliant

The CA3130 is an ideal choice for the type of comparator cir-
cuit shown in Figure 41 because it can “compare” low
voltages (such as those generated by a thermocouple) in the
proximity of the negative supply rail. Adjustment of potenti-
ometer R
reference voltages over the range of 0 to 20mV can be
applied to noninverting terminal 3 of the comparator. When-
ever the voltage developed by the thermocouple at terminal
2 is more positive than the reference voltage applied at ter-
minal 3, the comparator output is toggled so as to sink
current from terminal 9 of the ZVS; gate pulses are then no
longer applied to the triac. As shown in Figure 41, the circuit
is provided with a control point “hysteresis” of 1.25mV.
Nulling of the comparator is performed by means of the fol-
lowing procedure: Set R
short the thermocouple output signal appropriately. If the
triac is in the conductive mode under these conditions,
adjust nulling potentiometer R
conduction is interrupted. On the other hand, if the triac is in
the nonconductive mode under the conditions above, adjust
R
thermocouple output signal should then be unshorted, and
R
cuit operation.
Machine Control and Automation
The earlier section on interfacing techniques indicated sev-
eral techniques of controlling AC loads through a logic
system. Many types of automatic equipment are not complex
enough or large enough to justify the cost of a flexible logic
system. A special circuit, designed only to meet the control
requirements of a particular machine, may prove more eco-
nomical. For example, consider the simple machine shown
in Figure 42; for each revolution of the motor, the belt is
advanced a prescribed distance, and the strip is then
punched. The machine also has variable speed capability.
The typical electromechanical control circuit for such a
machine might consist of a mechanical cambank driven by a
separate variable speed motor, a time delay relay, and a few
logic and power relays. Assuming use of industrial grade
controls, the control system could get quite costly and large.
Of greater importance is the necessity to eliminate transients
generated each time a relay or switch energizes and deener-
5
1
can be set to the voltage threshold desired for control cir-
to the point at which triac conduction commences. The
ONE REVOLUTION OF
MOTOR ADVANCES
BELT ONE INDEX
DISTANCE
1
FIGURE 42. STEP-AND-PUNCH MACHINE
drives the voltage divider network R
MOTION
PUNCH
1
SOLENOID
at the low end of its range and
VALVE
5
to the point at which triac
SOURCE
LIGHT
Application Note 6182
3
PHOTOCELL
, R
4
so that
20
gizes the solenoid and motor. Figure 43 shows such
transients, which might not affect the operation of this
machine, but could affect the more sensitive solid-state
equipment operating in the area.
A more desirable system would use triacs and zero-voltage
switching to incorporate the following advantages:
1. Increased reliability and long life inherent in solid-state de-
2. Minimized generation of EMI/RFI using zero-voltage
3. Elimination of high voltage transients generated by relay
4. Compactness of the control system.
The entire control system could be on one printed circuit
board, and an overall cost advantage would be achieved.
Figure 44 is a timing diagram for the proposed solid-state
machine control, and Figure 45 is the corresponding control
schematic. A variable speed machine repetition rate pulse is
set up using either a unijunction oscillator or a transistor a
stable multivibrator in conjunction with a 10ms one shot mul-
tivibrator. The first zero voltage switch in Figure 45 is used to
synchronize the entire system to zero-voltage crossing. Its
output is inverted to simplify adaptation to the rest of the cir-
cuit. The center zero-voltage switch is used as an interface
for the photocell, to control one revolution of the motor. The
gate drive to the motor triac is continuous DC, starting at
zero voltage crossing. The motor is initiated when both the
machine rate pulse and the zero-voltage sync are at low volt-
age. The bottom zero-voltage switch acts as a time delay for
pulsing the solenoid. The inhibit input, terminal 1, is used to
assure that the solenoid will not be operated while the motor
is running. The time delay can be adjusted by varying the
reference level (50K potentiometer) at terminal 13 relative to
the capacitor charging to that level on terminal 9. The capac-
itor is reset by the SCR during the motor operation. The gate
drive to the solenoid triac is direct current. Direct current is
used to trigger both the motor and solenoid triacs because it
is the most desirable means of switching a triac into an
inductive load. The output of the zero-voltage switch will be
continuous DC by connecting terminal 12 to common. The
FIGURE 43. TRANSIENTS GENERATED BY RELAY CONTACT
vices as opposed to moving parts and contacts associated
with relays.
switching techniques in conjunction with thyristors.
contact bounce and contacts breaking inductive loads, as
shown in Figure 42.
INDUCTIVE
CURRENT
TURN-ON
VOLTAGE
RANDOM
LOAD
LINE
BOUNCE AND NONZERO TURN OFF OF INDUC-
TIVE LOAD.
CONTACT
BOUNCE
TURN-OFF
RANDOM
LENGTH
OF ARC