CN-6 - Triac Control Using the COP400 Microcontroller...

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TL/DD/6939 Triac Control Using the COP400 Microcontroller Family CN-6 National Semiconductor COP Note 6 February 1981 Triac Control Using the COP400 Microcontroller Family Table of Contents 1.0 TRIAC CONTROL 1.1 Basic Triac Operation 1.2 Triggering 1.3 Zero Voltage Detection 1.4 Direct Couple 1.5 Pulse Transformer Interface 1.6 False Turn-on 2.0 SOFTWARE TECHNIQUES 2.1 Zero Voltage Detection 2.2 Processing Time Allocations Half Cycle Approach Full Cycle Approach 2.3 Steady State Triggering 3.0 TRIAC LIGHT INTENSITY CONTROL CODE 3.1 Triac Light Intensify Routine 1.0 Triac Control The COP400 single-chip controller family members provide computational ability and speed which is more than ade- quate to intelligently manage power control. These control- lers provide digital control while low cost and short turn- around enhance COPS TM desirability. The COPS controllers are capable of 4 m s cycle times which can provide more than adequate computational ability when controlling 60 Hz line voltage. Input and output options available on the COPS devices can contour the device to apply in many electrical situations. A more detailed description of COPS qualifica- tions is available in the COP400 data sheets. The COPS controller family may be utilized to manage pow- er in many ways. This paper is devoted to the investigation of low cost triac interfaces with the COP400 family micro- controller and software techniques for power control appli- cations. 1.1 BASIC TRIAC OPERATION A triac is basically a bidirectional switch which can be used to control AC power. In the high-impedance state, the triac blocks the principal voltage across the main terminals. By pulsing the gate or 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; however, this does affect the gate current requirements. Gate current requirements vary depending on the direction of the main terminal current and the gate current. The four trigger modes are illustrated in Figure 1 . TL/DD/6939–1 FIGURE 1. Gate Trigger Modes. Polarities Referenced to Main Terminal 1. COPS TM is a trademark of National Semiconductor Corporation. C 1995 National Semiconductor Corporation RRD-B30M105/Printed in U. S. A.
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The breakover voltage (V BO ) is specified with the gate cur- rent (I GT ) equal to zero. By increasing the gate current sup- plied to the triac, V BO can be reduced to cause the triac to go into the conduction or on state. Once the triac has en- tered the on state the gate signal need not be present to sustain conduction. The triac will turn itself off when the main terminal current falls below the minimum holding cur- rent required to sustain conduction (I H ).
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CN-6 - Triac Control Using the COP400 Microcontroller...

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