CA3059

Manufacturer Part NumberCA3059
DescriptionZERO VOLTAGE CROSSING SWITCH
ManufacturerIntersil
CA3059 datasheet
 


Specifications of CA3059

Rohs StatusRoHS non-compliant  
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V
V
PIN 9
PIN 9
V
PIN 13
V
LOAD
120V
60Hz
and scorching of any type is minimized.
10K
220V
8W
60Hz
5
2
3
13
ZVS
100 F
10 F
7
+
16V
+
15V
T
8
9
1K
22K
+
25 F
100K
270
15V
FIGURE 17. SCHEMATIC DIAGRAM OF PROPORTIONAL ZERO-
VOLTAGE SWITCHING CONTROL
FIGURE 18. WAVEFORMS FOR THE CIRCUIT OF FIGURE 17.
Effect of Thyristor Load Characteristics
The zero-voltage switch is designed primarily to gate a thy-
ristor that switches a resistive load. Because the output
pulse supplied by the switch is of short duration, the latching
current of the triac becomes a significant factor in determin-
ing whether other types of loads can be switched. (The
latching current value determines whether the triac will
remain in conduction after the gate pulse is removed.) Provi-
sions
are
included
in
the
zero-voltage
accommodate inductive loads and low power loads. For
example, for loads that are less than approximately 4A
that are slightly inductive, it is possible to retard the output
pulse with respect to the zero-voltage crossing by insertion
of the capacitor C
from terminal 5 to terminal 7. The inser-
X
tion of capacitor C
permits switching of triac loads that have
X
a slight inductive component and that are greater than
approximately 200W (for operation from an AC line voltage
of 120V
). However, for loads less than 200W (for exam-
rms
ple, 70W), it is recommended that the user employ sensitive
gate triacs with the zero-voltage switch because of the low
latching current requirement of this triac.
For loads that have a low power factor, such as a solenoid
valve, the user may operate the zero-voltage switch in the
DC mode. In this mode, terminal 12 is connected to terminal
7, and the zero crossing detector is inhibited. Whether a
“high” or “low” voltage is produced at terminal 4 is then
dependent only upon the state of the differential comparator
Application Note 6182
within the integrated circuit zero-voltage switch, and not
upon the zero crossing of the incoming line voltage. Of
V
V
PIN 13
PIN 13
course, in this mode of operation, the zero-voltage switch no
longer operates as a zero-voltage switch. However, for may
applications that involve the switching of low current induc-
V
PIN 9
tive loads, the amount of RFI generated can frequently be
tolerated.
For switching of high current inductive loads, which must be
turned on at zero line current, the triggering technique
employed in the dual output over-under temperature control-
ler and the transient free switch controller described
subsequently in this Note is recommended.
Switching of Inductive Loads
TO
For proper driving of a thyristor in full cycle operation, gate
HEATER
ELEMENT
drive must be applied soon after the voltage across the
device reverses. When resistive loads are used, this reversal
occurs as the line voltage reverses. With loads of other
power factors, however, it occurs as the current through the
4
load becomes zero and reverses.
G
T
1
There are several methods for switching an inductive load at
the proper time. If the power factor of the load is high (i.e., if
the load is only slightly inductive), the pulse may be delayed
by addition of a suitable capacitor between terminals 5 and
7, as described previously. For highly inductive loads, how-
ever, this method is not suitable, and different techniques
must be used.
If gate current is continuous, the triac automatically commu-
tates because drive is always present when the voltage
reverses. This mode is established by connection of termi-
nals 7 and 12. The zero crossing detector is then disabled so
that current is supplied to the triac gate whenever called for
by the sensing amplifier. Although the RFI eliminating func-
tion of the zero-voltage switch is inhibited when the zero
crossing detector is disabled, there is no problem if the load
is highly inductive because the current in the load cannot
change abruptly.
Circuits that use a sensitive gate triac to shift the firing point
of the power triac by approximately 90 degrees have been
designed. If the primary load is inductive, this phase shift
switch
to
corresponds to firing at zero current in the load. However,
changes in the power factor of the load or tolerances of com-
or
rms
ponents will cause errors in this firing time.
The circuit shown in Figure 19 uses a CA3086 integrated
circuit transistor array to detect the absence of load current
by sensing the voltage across the triac. The internal zero
crossing detector is disabled by connection of terminal 12 to
terminal 7, and control of the output is made through the
external inhibit input, terminal 1. The circuit permits an
output only when the voltage at point A exceeds two V
drops, or 1.3V. When A is positive, transistors Q
conduct and reduce the voltage at terminal 1 below the
inhibit state. When A is negative, transistors Q
conduct. When the voltage at point A is less than 1.3V,
neither of the transistor pairs conducts; terminal 1 is then
pulled positive by the current in resistor R
inhibited.
9
BE
and Q
3
4
and Q
1
2
, and the output is
3