07-06-2013, 04:22 PM
Motor Control Using Triac Application Note
[attachment=54967]
Introduction
This application note describes a simple method for controlling a motor using a triac and a means
of detecting the zero crossing on 50 Hz power systems with voltages up to 230 Vac. R8C/1A is a
flash MCU that provide a low cost and high performance solution for traic control. The minimum
execution time for high speed instruction processing is 125ns using the on-chip oscillator. There are
many other useful peripheral functions on MCU that can be used for future improvements.
Other Renesas products that used in this application example are BCR08AM-12 (Triac) and
1N4148 (Diode).
In additional to this application note, the manuals listed below are available for reference for
developing applications.
Application
Low power triacs are used in many applications such as light dimmers, speed controls for electric
fans, electric motors and control circuits of many household appliances such as washing machines,
vacuum cleaners and drilling machines.
Basic Triac Operation
A triac is basically a bidirectional electronic switch, which can conduct current in either direction
when it is triggered. The triggering can be either a positive or negative voltage applied to its gate
electrode. By applying a steady state gate signal, the triac may be triggered into a low impedance
state where conduction across the main terminals will occur. The gate signal polarity need not
follow the main terminal polarity. Gate requirement vary depending on the direction of the main
terminal current and the gate current.
Traic controlled AC switching is referenced to the AC 50 Hz line frequency, which enables precise
control over the conduction angle at which the triac is fired. This enables the R8C device to control
the power output by increasing or decreasing the conduction angle in each half cycle.
Phase Control
The application example uses a phase control method for controlling the amount of power delivered
to the load. Phase control works by turning on a fraction of each half wave. The power delivered
will be proportional to the area under the curve. The benefit of the phase control is that the
frequency of the waveform providing power to the load is unchanged at 50 Hz.
Application Example
The application example uses a low cost R8C/1A to control an AC motor using BCR08AM. A
program is written to detect the zero crossing of the AC signal and in turn control the triac to
provide power to the AC motor. This application note provides a convenient and simple solution
for testing or further development for motor control using a triac.
Power Supply
The power supply circuitry is a resistive transformerless power supply. A 5V zener diode (D1) and
some circuit components are used to provide 5V to the rest of the motor control board. This design
is smaller and cheaper than a transformer based power supply. The fuse (F1) and varistor (V1) are
used to provide additional safety protection to the power supply circuit.
Detection Circuits
For this application example, the zero crossing waveform can be detected from the power supply
circuit. On the power supply circuit which provides a 5V pulse at the zero crossing point of a ac
waveform, this 5V pulse will be sent to a R8C/1A hardware interrupt port <P4_5/INT>. This signal
will inform the program that a zero crossing has been detected and it should start processing the
conduction angle. The conduction angle is counted by means of a timer counter. After R8C/1A has
reached the conduction angle or after the timer counter has stopped, the program will send a pulse
to activate the triac control circuit. The triac will be fired during the conduction angle chosen by the
program. The motor will be turned on at the speed determined by the time it is turned on and is
proportional to the power supplied to it.
[attachment=54967]
Introduction
This application note describes a simple method for controlling a motor using a triac and a means
of detecting the zero crossing on 50 Hz power systems with voltages up to 230 Vac. R8C/1A is a
flash MCU that provide a low cost and high performance solution for traic control. The minimum
execution time for high speed instruction processing is 125ns using the on-chip oscillator. There are
many other useful peripheral functions on MCU that can be used for future improvements.
Other Renesas products that used in this application example are BCR08AM-12 (Triac) and
1N4148 (Diode).
In additional to this application note, the manuals listed below are available for reference for
developing applications.
Application
Low power triacs are used in many applications such as light dimmers, speed controls for electric
fans, electric motors and control circuits of many household appliances such as washing machines,
vacuum cleaners and drilling machines.
Basic Triac Operation
A triac is basically a bidirectional electronic switch, which can conduct current in either direction
when it is triggered. The triggering can be either a positive or negative voltage applied to its gate
electrode. By applying a steady state gate signal, the triac may be triggered into a low impedance
state where conduction across the main terminals will occur. The gate signal polarity need not
follow the main terminal polarity. Gate requirement vary depending on the direction of the main
terminal current and the gate current.
Traic controlled AC switching is referenced to the AC 50 Hz line frequency, which enables precise
control over the conduction angle at which the triac is fired. This enables the R8C device to control
the power output by increasing or decreasing the conduction angle in each half cycle.
Phase Control
The application example uses a phase control method for controlling the amount of power delivered
to the load. Phase control works by turning on a fraction of each half wave. The power delivered
will be proportional to the area under the curve. The benefit of the phase control is that the
frequency of the waveform providing power to the load is unchanged at 50 Hz.
Application Example
The application example uses a low cost R8C/1A to control an AC motor using BCR08AM. A
program is written to detect the zero crossing of the AC signal and in turn control the triac to
provide power to the AC motor. This application note provides a convenient and simple solution
for testing or further development for motor control using a triac.
Power Supply
The power supply circuitry is a resistive transformerless power supply. A 5V zener diode (D1) and
some circuit components are used to provide 5V to the rest of the motor control board. This design
is smaller and cheaper than a transformer based power supply. The fuse (F1) and varistor (V1) are
used to provide additional safety protection to the power supply circuit.
Detection Circuits
For this application example, the zero crossing waveform can be detected from the power supply
circuit. On the power supply circuit which provides a 5V pulse at the zero crossing point of a ac
waveform, this 5V pulse will be sent to a R8C/1A hardware interrupt port <P4_5/INT>. This signal
will inform the program that a zero crossing has been detected and it should start processing the
conduction angle. The conduction angle is counted by means of a timer counter. After R8C/1A has
reached the conduction angle or after the timer counter has stopped, the program will send a pulse
to activate the triac control circuit. The triac will be fired during the conduction angle chosen by the
program. The motor will be turned on at the speed determined by the time it is turned on and is
proportional to the power supplied to it.