tca280b Hendon Semiconductors, tca280b Datasheet - Page 6

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

Integrated Electronic Solutions, Hendon, South Australia
7
The TCA280B contains four circuits,
that may be interconnected to
perform the functions required, and a
supply section. The four circuits are a
zero-crossing detector, a differential
amplifier, a sawtooth generator and
an output stage.
7.1
The TCA280B may be supplied by an
external DC power supply connected
to Vcc (pin 11), but can be supplied
directly from the mains voltage. For
this purpose the circuit contains a
number of stabilizer diodes, and a
transistor connected between V
and V
voltage. An external resistor Rd and
an external diode (mains voltage
rated) has to be connected from the
mains to RX2; V
neutral line (see Figs 5 and 6). A
smoothing capacitor C1 has to be
connected between V
The circuit produces a positive supply
voltage at V
supply an external circuit such as a
temperature sensing bridge.
An external diode in series with the
resistor Rd must be included (see
Figs 5 and 6). The maximum reverse
current (10 A) through pin 13 must
not be exceeded or circuit operation
cannot be guaranteed. Note that the
diode also reduces the required
power rating of resistor Rd by nearly
50%.
During the positive half of the mains
cycle the current through the external
voltage dropping resistor Rd charges
the external smoothing capacitor C1
to the stabilizing voltage of the
internal stabilizer diodes/transistor
network. The value of Rd should be
chosen such that it can supply the
current for the TCA280B (see Fig.4)
plus any current drawn by an external
(peripheral) circuit connected to V
and recharge the smoothing capacitor
2002 Nov 08
General purpose triggering circuit
FUNCTIONAL DESCRIPTION
EE
Supply: Vcc and RX2 (pins
11 and 13)
, that limit the DC supply
CC
, this may be used to
EE
is connected to the
CC
and V
EE
CC
.
CC
C1. Any excess current is bypassed
by the internal diode/ transistor
stabilizing network. The maximum
rated current must not be exceeded.
During the negative half of the mains
cycle the external smoothing
capacitor supplies the circuit. Its
capacitance must be high enough to
maintain the supply voltage above the
minimum specified limit. For values of
Rd and C1 see Figs 5 and 6.
A suitable VDR connected across the
mains provides protection for the
TCA280B and the triac against
mains-borne transients.
7.2
The TCA280B contains a zero-
crossing detector to produce pulses
that coincide with the zero crossings
of the mains voltage for minimum RF
interference and transients on the
mains supply.
The pulse width control input PW
(pin 1) allows adjustment of the pulse
width at output QZ (pin 2), to the value
required for the triac, by choosing the
value of the external synchronization
resistor RS between PW and the AC
mains. The pulse width is inversely
proportional to the input current and
to the mains frequency. The
zero-crossing detector is inhibited
when the ENZ input (pin 12) is HIGH,
and enabled when ENZ is LOW, e.g.
connected to V
Output QZ, which produces
negative-going output pulses, is an
n-p-n open-collector output that
requires an external resistor
connected to V
7.3
IC+ and IC (pins 5 and 6) are
differential inputs of a comparator or
differential amplifier, with QC+ and
QC (pins 4 and 7) as complementary
outputs. QC+ and QC are p-n-p
open collector outputs requiring
external collector resistors to V
Zero-crossing detector
Comparator
EE
CC
.
.
5
EE
.
QC+ will be HIGH and QC will be
LOW when IC+ is higher than IC .
The comparator contains a long-
tailed pair with a current source in its
tail. The tail current is activated by a
current into RX1 (pin 3). When an
inductive load is driven with phase
control the trigger pulse may be.
terminated at the instant of firing of
the thyristor or triac. This may be
achieved by connecting RX1 via a
resistor to the anode of the thyristor or
triac.
7.4
The sawtooth generator may be used
to produce bursts of trigger pulses,
with the net effect that the load is
periodically switched on and off. The
heart of the sawtooth generator is a
thyristor arrangement. The firing burst
repetition time is usually determined
by an external resistor and capacitor
connected to the sawtooth generator
trigger input IS (pin 14). The repetition
time is typical 0.7 x RC.
The output QS (pin 15) is an n-p-n
open-collector output. During the
flyback period of the sawtooth pulse
the transistor is ON and is capable of
sinking current.
7.5
The output stage is driven by current
drawn from input IA (pin 9). This drive
may be inhibited by drawing current
from inhibiting input INHA (pin 8).
Hence the output will be HIGH only if,
current is drawn from IA and no
current is from of INHA i.e. if inhibiting
input INHA (pin 8) is HIGH and input
IA (pin 9) is LOW. Both inputs may be
used as a single input provided the
other one is suitably biased.
The output QA (pin 10) is an n-p-n
open-emitter output capable of
sourcing an output current i.e.
conventional current flow out of the
circuit.
Sawtooth generator
Output stage
TCA280B
Data Sheet