COP8SA-DM National Semiconductor, COP8SA-DM Datasheet - Page 209

• Manufacturer Part Number: COP8SA-DM
• Description: MODULE DEBUGGING FOR COP8SA
• Manufacturer: National Semiconductor

Specifications of COP8SA-DM

• Module/board Type: Debugger Module
• For Use With/related Products: Cop 8
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: *COP8SA-DM

4.5
TRIAC CONTROL
The COP8SAx7 family of devices provide the computational ability and speed that is
suitable for intelligently managing power control. In order to control a triac on a cyclic
basis, an accurate time base must be established. This may be in the form of an AC 60Hz
sync pulse generated by a zero voltage detection circuit or a simple real-time clock. The
COP8SAx7 family is suited to accommodate either of these time base schemes while
accomplishing other tasks.
Zero voltage detection is the most useful scheme in AC power control because it affords
a real-time clock base as well as a reference point in the AC waveform. With this
information it is possible to minimize RFI by initiating power-on operations near the AC
line voltage zero crossing. It is also possible to fire the triac only a portion of the cycle,
thus utilizing conduction angle manipulation. This is useful in both motor control and
light-intensity control.
COP8SAx7 program is capable of compensating for noisy or semi-accurate zero voltage
detection circuits. This is accomplished by using delays and debounce algorithms in the
software. With a given reference point in the AC waveform, it becomes easy to divide the
waveform to efficiently allocate processing time.
These techniques are demonstrated in the following code listing. This application
example is based on the half cycle approach of AC power for triac light intensity control.
The code intensifies and deintensifies a lamp under program control.
This program example is not intended to be a final functional program. It is a general-
purpose light intensifying/deintensifying routine which can be modified for a light
dimmer application. The delay routines are based on a 10 MHz crystal clock (1
s
instruction cycle). The COP8SAx7’s 16-bit timer can be used for timing the half cycle of
an AC power line, and the timer can be started or stopped under software control. Timer
T1 is a read/write memory mapped counter with two associated 16-bit auto-reload
registers. In this example, only one reload register is used because the timer is stopped
after each timer reload from R1A. Zero crossings of the 60 Hz line are detected and
software debounced to initiate each half cycle, so the triac is serviced on every half cycle
of the power line. This program divides the half cycle of a 60 Hz AC power line into 16
levels. Intensity is varied by increasing or decreasing the conduction angle by firing the
triac at various levels. Each level is a fixed time which is loaded into the timer. Once a
true zero cross is detected, the timer starts and the triac is serviced.
A level/sublevel approach is utilized to vary the conduction angle and to provide a
prolonged intensifying period. The maximum intensity reached is at the maximum
conduction angle (level), and the time required to get to that level is loaded into the timer
in increments. Once a level has been specified, the remaining time in the half cycle is
then divided into sublevels. The sublevels are increased in steps to the maximum level
and the triac is fired 16 times per sublevel, thus creating the intensity time base. For
deintensifying, the sublevels are decremented.
COP8SAx7 APPLICATION IDEAS
4-17