tca280b Hendon Semiconductors, tca280b Datasheet - Page 18

• Manufacturer Part Number: tca280b
• Description: General Purpose Triggering Circuit
• Manufacturer: Hendon Semiconductors

Integrated Electronic Solutions, Hendon, South Australia
10.3
The function of the zero-crossing.
detector (Fig. 12) is to synchronize
the trigger pulses with the mains
voltage when the trigger module is
used as a static switch or as a
time-proportional switch.
If the load is purely resistive, the
synchronization voltage is obtained
direct from the mains via a resistor.
As a result trigger pulses start shortly
before, and end shortly after, each
zero-crossing of the mains voltage. In
this manner radio interference is
reduced to a minimum.
2002 Nov 08
General purpose triggering circuit
Zero-crossing detector
Vin
+
−
16
11
R2
5.2
kΩ
R1
25 kΩ
D6
If the load contains an inductive
component, the synchronization
voltage is taken from terminal 2 of the
triac. The trigger pulse is then
produced at the earliest possible
moment, i.e. immediately following
zero-crossing of the phase-shifted
load current. The pulse is initiated by
the step function of the synchronizing
voltage when the triac is turned off.
In phase control the zero-crossing
detector is used to generate a
sawtooth voltage synchronous with
the mains. As soon as the d.c. control
voltage corresponding to a preset
TR2
R3
31
kΩ
Fig.12 Zero-crossing detector
TR3
D8
D7
3.8 kΩ
R4
Vin
PW
D9
1
TR4
D10
17
ENZ
12
TR5
R5
300
Ω
10.1
R6
kΩ
TR6
R7
26
kΩ
TR7
2
RX1
+
trigger angle is exceeded, this voltage
starts the trigger pulse. Depending on
the direction and the value of the
current through pin 1, the output
transistor TR7 will be activated. If a
positive current of 50 A flows
through pin 1, the current through R3
will flow through TR2 to pin 16, if a
negative current of 50 A flows
through pin 1, the current through R3
will find its way to pin 16 via TR3. In
both cases the output transistor TR7
is not activated.
Fig-12-cct
−
from output
amplifier
Vout
to TR18
of ramp
function
generator
TCA280B
Data Sheet