2002 Nov 08
8
Integrated Electronic Solutions, Hendon, South Australia
Data Sheet
General purpose triggering circuit
OM5428
10 IMPORTANT: ELECTRICAL SAFETY WARNING
OM5428 circuit is connected to the mains electrical supply
and operates at voltages which need to be protected by
proper enclosure and protective covering. Application
circuits for OM5428 should be designed to conform to
relevant standards (such as IEC 65, or Australian
Standards AS3100, AS3250 and AS3300), it should only
be used in a manner that ensures the appliance in which
they are used complies with all relevant national safety and
other Standards.
It is recommended that a printed circuit board using this
integrated circuit be mounted with non-conductive clips,
and positioned such that the minimum creepage distances
from the assembly to accessible metal parts, and between
high voltage points cannot be transgressed.
It should be noted that as there are Mains Voltages on the
circuit board adequate labelling should be attached to
warn service personnel, and others, that this danger
exists.
A control board assembly should be mounted, preferably
vertically, with sufficient free air flow across its surface to
prevent the heat dissipated in various components from
causing an unacceptable rise in the ambient temperature.
The triac also needs to have an adequate heatsink, as
exceeding its rated maximum junction temperature can
result in loss of control, unpredictable behaviour, and
possible dangerous conditions.
The board should be mounted in a place that is clean and
dry at all times, not subject to condensation or the
accumulation of dust and other contaminants.
11 APPLICATION INFORMATION
The reliability of modern triacs has
given a strong impetus to the
introduction of electronic power
control in industrial as well as
non-industrial areas. Because of the
low cost of these devices and
simplification in trigger circuitry,
electronic power control now enjoys a
host of applications such as electronic
household cookers, panel radiators,
fans, hobby tools, and even vacuum
cleaners.
The general purpose trigger circuit
OM5428, referred to as a trigger
module, supplies the pulses for gate
triggering triacs. This module is
connected to the mains via a dropping
resistor hence removing the need for
an expensive external supply.
The OM5428 is an inexpensive,
versatile trigger module and, being a
monolithic IC in 16-pin dual in-line
package, it takes up hardly any space
at all. It is ideally suited for
applications such as:
1.
On/off control: static switch.
On/off control is a method of
power control where triggering
should preferably occur
symmetrically with respect to the
zero crossing of the triac current
to avoid RF interference. That is,
triggering must start before the
current has dropped to the
holding value, and must continue
until the current has risen again
above the latching level. Under
these conditions radio
interference is kept at a minimum.
2.
Time proportional control:
temperature and motor speed
control.
Time proportional control is on/off
control with a fixed repetition rate
of load switching. The system is
called time proportional because
the power in the load averaged
over the repetition period is
varied. This system provides
more accurate temperature
control, avoiding the overshoot
which is inherent in on/off control.
Triggering conditions are the
same as for on/off control.
3.
Phase control: single phase
control (full cycle).
Phase control is stepless control
of output power by varying the
conduction angle of the triac, 180
degree conduction corresponding
to full output power. Step
changes in triac voltage and
current during turn-on give rise to
RF interference. Appropriate RF
interference suppression
methods need to be applied for all
phase triggered loads.
It should be noted that phase
control is not permitted for
heating purposes.
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