Dimming Incandescent Lamps Using PIC10F200 WARNING This symb
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TB094
Dimming Incandescent Lamps Using PIC10F200
WARNING
This symbol indicates that building using system described this document will expose electric shock.
Only persons experienced electrical manufacture should this document complete system described. FAILURE FOLLOW PROPER SAFETY PRECAUTIONS COULD RESULT PERMANENT INJURY DEATH ELECTRIC SHOCK HAZARDS. avoid risk injury from electric shock, build, use, system described this document without implementing proper safety measures. Microchip Technology Inc. makes representation that system shown this document meets standards that govern performance, consumer safety, electrical interference characteristics system described herein. recommend that contact applicable governing body your geography determine standards which should manufacture your system. Author: Keith Curtis Microchip Technology Inc. Generating delayed triggering triac initially involved network with variable which created required time delay. However, simple circuit gate drive, still suffers from nonlinearity's sinusoidal shape waveform. Production dimmers alleviated this problem creating custom potentiometer with nonlinear resistance curve, which approximated linear dimming. But, high voltages involved, there still significant amount heat dissipated resistor. what about using microcontroller control triac? generate appropriate timing delay using table produce linear dimming curve, microcontroller opens number user interface possibilities. Unfortunately, microcontrollers line voltages, they need low-voltage power supply operate. Transformerless designs supply lower voltage, their efficiency would still dissipate significant amount heat. this point that nano-Watt technology comes rescue. Given extremely low-current consumption, possible reduce heat generated transformerless power supply down reasonable levels. Note: mention EMI/RFI filtering made this design. production design must have EMI/RFI filtering prevent noise generated part dimming progress from interfering with external systems.
INTRODUCTION
earliest circuits home electronics venerable incandescent lamp dimmer. also most challenging circuits right. this technical brief will examine using microcontroller both simplify circuit make efficient.
THEORY
Early dimmers were very simple circuits, much more than high-current rheostat (variable resistor) wired series with lamp. low-light conditions, adjusted high resistance, reducing current through lamp filament. high-light conditions, adjusted resistance increasing current flow filament. However, because essentially current limiting resistor, typically dissipated heat, especially middle range. search more efficient method dimming. With advent semiconductor thyristors, method dimming born. method dimming involved delaying turn-on time triac until controlled time after each zero crossing. Because zero crossing resets triac (turning off), delay essentially pulse width modulated lamp, delivering only portion potential current each cycle dimming lamp.
2005 Microchip Technology Inc.
DS91094A-page
TB094
HARDWARE
nano-Watt microcontroller used generate feature rich dimmer design. this design, will designing dimmer incandescent lamps with following features. Capable delivering 100-200 Watts power VAC. user interfaces; based infrared remote control system, second based interruptions supply caused user toggling switch existing in-house switched outlet. Low-power dissipation, resistor-based transformerless power supply. Small form factor. when choose triac, will want small sensitive-gate triac capable switching amps. should have minimal hold current requirement limit amount time that will have supply gate current. addition, power supply must have rail tied same line triac, avoid bias quadrant four. This will cause circuit only sink current triac gate, forcing operation quadrants three. L6004D3 device from Teccor only requires typical gate current drive minimum hold current less than addition, device available small package compact circuit. Assume that load Watt light bulb with typical filament resistance approximately triac should conducting when line voltage reaches Translating this into conduction angle, hold current should have been reached degrees following zero crossing (see Equation
first step design choose triac switching circuit. order make informed decision, will need cover triac basics first. triac essentially Silicon Controlled Rectifiers, SCR, cross-connected with their gate inputs tied together. Because based, once device begins conducting, will continue conduct until current flowing through device goes zero. operation, triac open circuit between supply lamp until minimum gate current either sourced sunk through gate pin. triac then latched until current through device goes zero next zero crossing waveform. While this description gives general idea device works, there specifics that missing. First all, triac does latch until minimum holding current flowing through device reached. Second, main pins triac completely interchangeable description implies. This because bias current triac dependent, extent, direction bias current direction load current device. These combinations current directions referred conduction quadrants device. Using convention main terminals, four quadrants defined follows: Quadrant one, current flow into MT1, with positive current flow into gate. Quadrant two, current flow into MT1, with negative current flow gate. Quadrant three, current flow into MT2, with negative current flow gate. Quadrant four, current flow into MT2, with positive current flow into gate. reason this important because minimum gate current quadrant four typically higher than quadrants through three. because will trying reduce current where possible, avoiding quadrant four operation desirable.
EQUATION
Angle invsin(5V/(110V 1.414))
Assuming system, minimum hold current should achieved after microseconds bias current (see Equation
EQUATION
Time (1/60 (2°/360°) only need hold bias current approximately latch triac average narrow pulse current over cycle, gives average current requirement triac bias less than 37.5 Note: Here significant advantages using microcontroller dimming. Because microcontroller only needs hold gate bias less than full half cycle, there savings over bias current triac, alone.
next challenge determine which nano-Watt device dimmer circuit. will need three I/O; triac gate drive, zero crossing detection data output from receiver module.
DS91094A-page
2005 Microchip Technology Inc.
TB094
smallest nano-Watt device meeting these requirements 6-pin PIC10F200 SOT-23 surface mount package. with input only pin, single current drive capability when powered running VDC, only requires microamps operate only 1/10th microamp when asleep. should perfect low-power microcontroller design. next requirement low-current receiver module remote control half user interface. should draw minimum current while operation capable receiving modulated beam decode into simple line output. Sharp GP1UD261RK fits requirements, operating from supply. draws current operate designed pull output when subjected light modulated kHz. that there three main components, must construct power budget design: receiver module will draw continuously. microcontroller will draw when operating less than 1/10th when asleep. triac will need average current less than
EQUATION
FILTER CAPACITOR CALCULATION
VRIPPLE)/5V
(-16 mS/((5V/.6
EQUATION
TIME SUPPLY DROOP
T(2V) In(2V/5V)*((5V/.4 mA)*330 T(2V) 3.77 seconds Given 1N4690 zener diode only requires 50-100 generate voltage VDC, current limiting resistors power supply will only have conduct total maintain output. line voltage split across resistors safety, this means each resistor will only dissipate assuming each resistor resistor (see Equation
EQUATION
(110VAC 1.414)/(100 Presistors ((110VAC 1.414 A)/2) resulting circuit shown Figure Note: extra PIC10F200 been used power supply receiver module. This done circuit power-down module when detects that line voltage been removed.
total current requirement system less than Quite savings considering that holding gate bias current full cycle would require times this current. Given power budget, design resistive transformerless power supply consisting two-current limiting resistors current 5.6V zener diode with equally current rectifier diode small filter capacitor (see Equation resulting supply will produce with ripple less than Further, receiver powered down, supply hold operating microcontroller least 3.77 seconds before falling below shutting down microcontroller (see Equation
2005 Microchip Technology Inc.
DS91094A-page
FIGURE
TB094
DS91094A-page L4004D3 MAC4DHMT4 Load .25A BAT54 MAZS0560ML MMBZ5232BLT1 1/8W 1/8W 1.2K ACin
PIC10F DIMMER
GP0/C+ GP1/CU1 PIC10F200
Programmer
GP2/T0CKI/CO GP3/MCLR
2005 Microchip Technology Inc.
GP1UD261RK
TB094
SOFTWARE
Note: When using programmer, circuit MUST disconnected from power FIRST!
REMOTE CONTROL
remote control system also based PIC10F200. uses wake-up change function wake whenever button pressed. then generates different modulated outputs, depending which button pressed. carrier frequency match receiver modules dimmer circuit. different modulations differentiate intensity Down commands, indicated button pressed wake remote. While button held down, firmware remote will repeat command pulse width. When button released, circuit then turns goes sleep conserve battery life. circuit remote control shown Figure microcontroller powered directly from lithium coin cell. push buttons connected inputs their ability generate wake-up change. transistor that drives driven GP2. more information Transmitter design, refer Application Notes regarding infrared connectivity listed Microchip site www.microchip.com.
software system relatively simple. When zero voltage crossing detected input, change state wakes microcontroller using Reset-on Change function pin. microcontroller wakes determines source reset checking GPWUF flags STATUS register. TB082, "Understanding Reset Events PIC10F20X", (DS91082), more information. Then microcontroller performs following: Checks state receiver module output. high, microcontroller moves determine appropriate delay triggering triac, based current intensity value. Waits delay. Generates pulse gate triac. Returns sleep.
output receiver module low, microcontroller first counts state then moves generate delay pulse. output receiver module high previous output sample low, firmware decodes command length makes appropriate change intensity value. Then moves determine appropriate delay, waits delay generates gate pulse triac before, once again, going sleep. secondary routine, wake-up change, keeps track total number wake-up change events. number sufficient hours operation, intensity value zero part timer-based shutdown conserve energy. microcontroller wakes Watchdog Timer time-out, wake-up change missed multiple cycles indicating that power been removed. firmware then powers down receiver module reduce power consumption increments intensity value system. secondary routine Watchdog Timer time-out counts number time-outs exceeds seconds, resets intensity value zero. This done part switched power user interface. power removed seconds, system assumes turned sets intensity value zero. However, with microcontroller sleeping majority time, there guarantee that supply voltage will drop below cause Power-up Reset microcontroller. this secondary routine been added back-up shutdown function.
2005 Microchip Technology Inc.
DS91094A-page
TB094
FIGURE REMOTE CONTROL TRANSMITTER
PIC10F200 ZXMN3A01F LN66
LiON GP0/C+ GP1/C-
GP2/T0CKI/CO GP3/MCLR
PRGMR
CONCLUSION
preceding sections, mentioned that microcontroller advantageous dimming circuit because compensate inherent nonlinearity dimming process. have seen this design process, also advantageous from power point view well. Keeping microcontroller Sleep mode reduces overall current draw minimal level. And, using minimal bias pulse fire triac further reduces current draw. Together savings over original triac bias current. cost only increase power supply current microcontroller, this leaves reduction circuit current draw over 78%. result significant savings power dissipated transformerless power supply design, which means much less expensive components used.
MEMORY USAGE
Dimmer
Program Memory words Data Memory bytes
Remote Control
Program Memory words Data Memory bytes
Documentation
AN954, "Transformerless Power Supplies, Resistive Capacitive", (DS00954) TB082, "Understanding Reset Events PIC10F20X", (DS91082)
DS91094A-page
2005 Microchip Technology Inc.
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2005 Microchip Technology Inc.
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