tca280b Hendon Semiconductors, tca280b Datasheet - Page 17

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

Integrated Electronic Solutions, Hendon, South Australia
10.2
Fig. 11 shows the circuit diagram of
the d.c. supply section. Pin 16 is the
common point of reference for the
supply, output, and control voltages,
as well as for the synchronizing
signals. This pin is connected to the
cathode of the thyristor or terminal 1
of the triac, and to one pole of the
mains. The other mains terminal is
connected to pin 13 via a dropping
resistor and series mains rated diode.
The regulator diodes D3, D4, and
transistor TR 1. form a voltage
stabilizing network of about 15 V
during the positive half cycle. The
voltage at pin 13 equals 15 V plus the
drop across D2, making it 15.7 V. The
block voltage across this network is
2002 Nov 08
General purpose triggering circuit
Current supply
further rectified by diode D5, and
smoothed by an electrolytic capacitor
C1 between pins 11 and 16 to serve
as the supply voltage (14.4 V) for the
other functional stages.
During the negative half-cycle, the
current is blocked by the external
diode in series with the supply
resistor. The total power loss in the
dropping resistor is reduced by about
50% by connecting the diode in series
with it. The value of Rd depends
mainly on the current required for
triggering the triac or the thyristor.
The minimum value of Rd is 4.7 k ,
as otherwise the maximum
permissible current through pin 13
would be exceeded (see the Limiting
Values table).
Fig.11 Connection of the d.c. supply
1
2
a.c.
load
TH1
Rd
16
D
RX2
13
16
D2
V EE
D1
D4
D3
TR1
V CC
D5
11
from output
amplifier, pin 10
If voltages higher or lower than 220 V
are used, an accordingly higher or
lower dropping resistor must be
connected to pin 13. If the trigger
module is fed direct from a d.c. power
supply, it is possible at voltages of 11
V to 17 V to have a direct connection
to pin 11. For some applications it is
recommended or even necessary to
keep the control circuit electrically
separated from the mains. This is
achieved with an isolating transformer
for circuit supply and synchronization.
In addition trigger transformers are
then needed to feed the trigger pulses
to the gate of the triac or thyristor.
C1
+
−
TCA280B
Data Sheet