(mcu) and triacs on the mains - W-R-E.de
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1. A NOTE AND OR THE USE MADE BY CUSTOMERS OF THE INFORMATION CONTAINED HEREIN IN CONNEXION WITH THEIR PRODUCTS Information furnished is believed to be accurate and reliable However STMicroelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use No license is granted by implication or otherwise under any patent or patent rights of STMicroelectronics Specifications mentioned in this publication are subject to change without notice This publication supersedes and replaces all information previously supplied STMicroelectronics products are not authorized for use as critical components in life support devices or systems without the express written approval of STMicroelectronics The ST logo is a registered trademark of STMicroelectronics 1998 STMicroelectronics All Rights Reserved Purchase of I C Components by STMicroelectronics conveys a license under the Philips 2C Patent Rights to use these components in an IC system is granted provided that the system conforms to the 1 C Standard Specification as defined by Philips STMicroelectronics Group of Companies Australia Brazil Canada China France Germany Italy Japan Korea Malaysia Malta Mexico Morocco The Netherlands Singapore Spain Sweden Switzerland Taiwan Thailand United Kingdom U S A http www st com 12 122. and the risk of saturation The circuit starts on a positive line halfwave and stops on a negative one Thus it starts with positive induction and stops after negative induction has been applied This helps to minimize the size of the magnetic core material and the current rating of the triac The timer is precisely tuned in order to obtain 8 3ms for 60Hz or 10ms for 50Hz delay be tween two gate pulses As a result the triac is driven symmetrically in both phases so that con tinuous voltage in the transformer is avoided and noise in the transformer is reduced Other wise the voltage across the triac is monitored to detect a spurious open load condition at the secondary of the transformer The inrush current at the turn on of a lamp halogen or incandescent is also reduced due to the soft start feature of the circuit fig 7 Triac drive The triac is directly driven by the MCU The pulse driving the triac is 50ms long The LOGIC LEVEL triac is driven in quadrants QII and QIII with a gate current of 20mA provided by two 1 O lines of the ST6210 in parallel The LOGICLEVEL triac has a maximum specified gate trig gering current of 10mA at 25 C The triac is multi pulse driven Therefore inductive loads can be driven without the use of long pulse drives As a result the consumption on the 5V supply can be minimized and the supply circuit becomes very small Before supplying the first drive pulse the triac voltage is tested If no volt
3. making simple modifications to the MCU EPROM ROM table defining the triac conduction angle versus power level Automatic selection of the 50Hz 60Hz tables could be done Figure 1 Mains synchronisation 4 2 12 MCU AND TRIAC ON THE MAINS A universal motor is an inductive load which may generate very strong dynamic constraints on the circuit at turn off Because of the phase lag of current with respect to voltage the reapplied voltage can be different from zero So the leading edge of the reapplied voltage across the triac can be very sharp because it is limited only by parasitic capacitances fig 8 A SNUB BERLESS triac is well adapted to this kind of loads because fast commutation characteristics can be obtained with low current rating devices Otherwise inrush current at motor startup is limited by the soft start feature included in the control Triac drive The triac is directly driven by the MCU The pulse driving the triac is short 100s in order to minimize the 5V supply circuit size The SNUBBERLESS triac is driven in quadrants QII and QIII with 60 mA gate current provided by three I O bits of the ST6210 in parallel This pulse is sufficiently long to insure the triac is latched at the end of the pulse Pulse length can be mod ified if another triac or motor is used User Interfaces There are three different user interfaces a touch control a push button and a potentiometer Four modes can be selected on the board in or
4. ITT APPLICATION NOTE MICROCONTROLLER AND TRIACS ON THE 110 240V MAINS by P Rabier L Perier INTRODUCTION Today electronics is used in home appliances for purposes as different as the motor regula tion of a washing machine the control of a vacuum cleaner the light dimming of a lamp or the heating in a coffee machine This pervasion increases rapidly because appliances require en hanced features easy to built and modify while electronics based solutions become cheaper and more sophisticated Within this evolution the microcontrollers MCU progressively replace analog controllers and discrete solutions even in low cost applications They are more flexible often need less com ponents and provide faster time to market With an analog IC the designer is limited to a fixed function frozen inside the device With a DIAC control features like sensor feedback or en hanced motor drive can not be easily implemented With the MCU proposed in this note the ST6210 the designer can include his own ideas and test them directly using EPROM or One Time Programmable OTP versions The triac is the least expensive power switch to operate directly on the 110 240V mains Thus it is the optimal switch for most of the low cost power applications operating on line The LOGIC LEVEL or SNUBBERLESS triacs are a complement to the ST6210 MCU for such ap pliances These triacs can operate with low gate current and can be directly triggered by the MCU whil
5. The major difference concerns the mains disturbances rejection in order to prevent lamp flickering The timing is carried out internally by the MCU timer The period of operation can be modified to follow the variations of the mains frequency but not the spurious disturbances The mains synchronisa tion signal is received every cycle Figure 7 Soft start with lamps HALOGEN LAMP AT THE SECONDARY OF A TRANSFORMER TRIAC ANODE CURRENT 1A div 200ms div TOOP Po A o H a E E E S PE a aa i i PEEN erate Serre ae m EEE T MAAAR RA AAA lh m HAULAGE Ro Re nations a ii ae a ee 240 V INCANDESCENT LAMP TRIAC ANODE CURRENT 1 A div 100 mol H d m L i i a Sa SEER EEE 9 12 4 MCU AND TRIAC ON THE MAINS The corresponding mains period is measured and compared to the internal timer period If a difference remains after many cycles the timer period is modified to follow the mains This block acts like a low band filter which eliminates external filtering components The user interface can be modified to fit other applications such as IR presence detection or alarm remote control etc PRACTICAL RESULTS Figure 7 presents the soft start operation with a halogen lamp operating from the secondary of a low voltage transformer and with a high voltage tungsten filament lamp With soft start the peak in rush current is about 3 times the nominal current compared with 10 to 15 times otherwise Therefore the lam
6. age is detected a spurious open load or a supply disconnection is assumed to have oc curred and the circuit is stopped After the first driving pulse the triac voltage is monitored If the triac is not ON another pulse is sent The same process can be repeated up to four times Then if the triac is still not ON the circuit is switched off Hardware The light dimmer board is almost the same as the motor drive board fig 6 The major differ ences concern the position where the voltage is measured and the triac choice When the board is dimming a resistive load an RFI filter should be added in order to the RFI standards i e VDE 875 In a dimmer because of the resistive load dynamic constraints are lower than in a motor con 8m2 STA MCU AND TRIAC ON THE MAINS trol soa LOGIC LEVEL triac BTA08 400SW or BTA08 600SW is used for safe gate current This triac has been especially designed to operate with a MCU It is a sensitive triac IGT lt 10mA which can be triggered in quadrants II and Ill This triac has high switching ca pabilities dl dt c gt 3 5A ms dV dt c gt 20V ms Thus it can also operate without a snubber in this circuit This board is supplied when the triac is off A minimum off time of the triac 1 7ms 60Hz and 2ms 50 Hz is necessary to ensure its supply The RCD circuit is the same as the one used for the motor drive board Software The light dimmer software is practically the same as with the motor drive
7. der to define how the transmitted power is re lated to the user interface Three modes operate with the touch sensor or the push button Dimming is obtained when the sensor or the button is touched for more than 330ms If the touch duration is between 50ms and 330ms the circuit is switched on or off A contact of less than 50ms causes no action Modes 1 2 3 differ in the way the motor speed is changed by sensor or button contact These values are given for the 60Hz version for a 50Hz mains values are respectively 400ms and 50ms Figure 2 User interfaces Sensor version potentiometer version VRO01812 4 3 12 MCU AND TRIAC ON THE MAINS Mode 4 directly relates transmitted power to potentiometer position fig 2 All modes include a soft start When operating together the SNUBBERLESS triac and the ST6210 MCU save components on the drive logic power supply mains connection and the power side fig 3 The MCU chosen ST6210 includes an 8 bit accumulator 2k ROM 64 bytes RAM an 8 bit A D converter that can be connected to 8 different inputs 4 I O lines with 10mA sink current ca pability and a timer Hysteresis protection is included in series with each I O pin The ST6210 is packaged in DIL or SMD packages The ports the timer and interrupts configurations can be chosen by software providing high flexibility The ST6210 has been designed to operate in very disturbed environments Each I O line contains internal diod
8. e loads Figure 5 Delay time in drive of an AC switch Main voltage 100 us div 10V div Gate pulse 100 us div 1V div 4 6 12 MCU AND TRIAC ON THE MAINS The figure 5 shows that a ST6210 can turn on a triac 35ms after the mains voltage zero crossing With such phase delay 0 75 60Hz and 0 63 50Hz the voltage reapplied across the load is small V and the leading edge of current is minimal Such an AC switch can include additional features such as voltage and current monitoring or feedback features This AC switch can also be used for instance in a refrigerator with smaller triacs with several compartments where the MCU controls different temperatures The MCU can then interface the sensors solve the priority conflicts and drive the AC switches with the optimal sequence LIGHT DIMMER Basic function The motor drive board can also operate as a light dimmer However the board can be slightly modified such that the neutral connection is no longer necessary Then the board can be plugged in series with the line wire like a mechanical switch The synchronization and the aux iliary supply are obtained from the voltage across the triac Fig 6 A light dimmer operating directly on the 110V or 240V mains has been realized using a MCU ST6210 and a LOGICLEVEL triac This circuit drives halogen or incandescent lamps supplied directly from the mains or through a low voltage transformer It includes softstart and protec tion again
9. e still maintaining a high switching capability This application note describes three different MCU based applications a universal motor drive an AC switch and a light dimmer They all operate with the same user interfaces and al most the same software and hardware AN392 1098 1 12 MCU AND TRIAC ON THE MAINS UNIVERSAL MOTOR DRIVE Basic function Universal motor drives with DIAC or analog controllers are currently used today These cir cuits have the disadvantage of requiring many external components when controls include so phisticated features such as speed control with torque limiting or when parameters have to be easily changed from one design to an other They are also limited in the choice of user inter faces A universal motor drive circuit supplied directly from the 110V 240V mains has been realized using a MCU ST6210 and a SNUBBERLESS triac The user interface is a touch sensor a push button or a potentiometer The board includes a minimum of components in order to save cost and size The auxiliary supply is derived from the mains voltage Power control The power device is a triac because it is the most economical on line switch The output power and therefore the motor speed are controlled by the phase delay of the triac drive This delay is referred to the zero crossing of the line voltage which is detected by means of a con nection to the mains neutral fig 1 Changing operation from 60Hz to 50Hz can be achieved by
10. erface or electronic shortcircuit protection with IGBT Mosfet can be implemented from these circuits Bibliography Thyristors and triacs application manual 1986 STMicroelectronics Universal Motor Speed Control P Rault Y Bahout 4 10 12 MCU AND TRIAC ON THE MAINS Figure 8 Universal motor drive Current and Voltage in the Triac TRIAC ANODE CURRENT 2A div 2ms div TRIAC VOLTAGE VAK 200 V div 2ms DIV Thyristors and triacs application manual 1989 STMicroelectronics Microcontroller based uni versal motor speed control M Queyrol ST62 user manual 1991 STMicroelectronics Power control with ST6210MCU and triac Ph Rabier L Perier 4 11 12 MCU AND TRIAC ON THE MAINS Table 1 Triacs and microcontrollers characteristics MICROCONTROLLERS eae amp OUTPUT SENSITIVITY CONNECTION CAPABILITIES PARAMETERS T amp TW SERIES Tx05 SERIES 1 I O BIT TRIAC S amp SW SERIES Tx10 SERIES Igt 10mMA 1 I O BIT TRIAC ST621x SERIES 2 1 O BITS IN ST622x SERIES E ears Gems PARALLEL TRIAG Io 20MA AT Vo 1 3V 3 I O BITS IN ene on PARALLEL TRIAC B amp BW ieee 4 I O BITS IN SERIES ore PARALLEL TRIAC THE PRESENT NOTE WHICH IS FOR GUIDANCE ONLY AIMS AT PROVIDING CUSTOMERS WITH INFORMATION REGARDING THEIR PRODUCTS IN ORDER FOR THEM TO SAVE TIME AS A RESULT STMICROELECTRONICS SHALL NOT BE HELD LIABLE FOR ANY DIRECT INDIRECT OR CONSEQUENTIAL DAMAGES WITH RESPECT TO ANY CLAIMS ARISING FROM THE CONTENT OF SUCH
11. es which clamp the input voltage between Vdd and Vss These diodes are sized to withstand a continuous current of 1mA typ With EPROM and OTP versions the equipment development and preproduction can be done directly from the design lab providing a fast time to market The SNUBBERLESS triac BTA 16 400CW for 110 V BTA10 600CW for 220V has been specially designed to drive loads which generate very strong dynamic constraints such as a vacuum cleaner motor This triac can be triggered in quadrants QI QII or QIII with gate and latching current of 35mA and 80mA respectively In this application it is driven by three I O lines of the ST6210 in parallel This triac has high current switching capability dl dt c gt 8 5A ms and 5 5A ms for BTA10 600CW and high static dv dt dV dt gt 250V ms So in this cir cuit it can operate without a snubber Figure 3 Motor drive circuit diagram ST62 TRIAC ON THE MAINS 1 10 240v OPTIONAL USER INTERFACES TOUCH SENSOR VERSION BTA 16 600CW Lae PUSH BUTTON Ov as 7 US E V OV 5V 3 AEA 4 POTENTIOMETER 22 aes f PO o VAN y v Ov ov mz NEUTRAL OETA 4 12 Figure 4 Major steps of the software 4 Delay time td2 in timer Calculation next delay Window for zero crossing mains MCU AND TRIAC ON THE MAINS Total consumption of the board is 3mA with an 8MHz oscillator The board supply comes from the mains through a simple RCD circuit The 5V is re
12. ferred to anode 1 of the triac in order to provide the negative gate current necessary to drive the triac in quadrants QII and QIll The 5V supply capacitance is mounted as near as possible to the MCU with very short interconnecting traces to maximize RFI immunity The touch sensor is a voltage divider be tween line and neutral It operates when the 5V supply input of the circuit is connected to the line potential This connection to the mains must be provided Software All operating features are contained in a 700 byte program More than 1byte of ROM is available for additional features The archi tecture of the software is modular in order to provide maximum flexibility A lockup table relating delay time to the power requirement contains 64 different levels The conduction time of the triac can vary from 1 7ms to 6 7ms for a 60Hz applica tion and from 2ms to 8ms to a 50Hz applica tion The user can easily adjust the minimum and maximum power levels because the cor responding delay times are slowly changing at the top and bottom of the table The table can be modified in ROM EPROM to meet dif ferent conditions e g 50Hz or 60Hz opera tion or varying loads One software version covers all four user in terface modes without hardware change All inputs are digitally filtered so that an input is validated only if it remains constant for 15s or more So passive filter components can be saved The mains supply carries distu
13. p life time is maximized blowing the input fuse is pre vented and the size of the triac is minimized The figure 8 presents the current and voltage in a triac driving a universal motor SUMMARY Microcontrollers MCU are in common use in most areas of electronics They are now set to penetrate the very cost sensitive area of home appliances The applications described in this paper show that enhanced appliance circuits can be designed with fast prototyping using a ST6210 MCU and a SNUBBERLESS or LOGIC LEVEL triac These circuits are low cost and they can provide more features with less components than classical solutions The presented circuits are a universal motor drive a AC switch and a light dimmer operating from the 110 240V mains The light dimmer drives incandescent and halogen lamps supplied either directly from the mains or through a low voltage transformer The motor drive can be adapted for instance to vacuum cleaners food processors drills or washing machines Those circuits include soft start and protection features Different user interfaces can be chosen touch sensor push button or potentiometer Such features are obtained with only few components a ST6210 MCU in 20pin DIL SMD package with a LOGIC LEVEL or SNUBBERLESS triac in T0220 package and some passive components Additional features like motor speed regulation torque limitation vacuum or unbalance con trol IR presence detection remote control alarm homebus int
14. r bances glitches telecommand signals which could disturb the triac drive For this reason a mains voltage zero crossing is only 5 12 MCU AND TRIAC ON THE MAINS validated if it occurs during a window of time 1 7ms each 16 6ms for 60Hz operation and 2ms each 200ms for 50Hz operation selected by the internal timer of the MCU This block acts as a filter and again eliminates external components fig 4 This circuit can be used as a basis for development of more sophisticated features such as vacuum regulation in a vacuum cleaner speed control in a food processor speed regulation with torque limiting ina drill unbalance detection in a washing machine or door opener with re mote control AC SWITCH AC switches operate as relays They have to turn on as soon as possible after a mains voltage zero crossing in order to prevent the disturbances induced by a sharp leading edge of current Their operating current has to be small in order to minimize the supply coming from the mains Also they are usually driven through isolated interfaces such as an optocoupler or trans former The motor drive circuit described previously can be used as a basis for such applications When the zero crossing of the mains voltage is detected this triac is turned on A SNUBBERLESS triac such as the BTA 16 600BW is suitable for an AC switch Its switching characteristics dl dt Jc gt 14A ms allows it to control various types of resistive and inductiv
15. st transformer saturation and against open load The user interfaces are the same as with the motor drive Figure 6 Light dimmer circuit diagram ST62 TRIAC LIGHT DIMMER USER INTERFACE gt TOUCH SENSOR f PUSH BUTTON OV POTENTIOMETER NEUTRAL 4 7 12 MCU AND TRIAC ON THE MAINS Power control Power is controlled by the phase delay td of the triac drive In the previous design td is re ferred to the zero crossing of the line voltage In order to avoid a connection to the mains neu tral and connect the circuit directly in series with the load the trigger delay is referred to the previous zero crossing of the current fig 1 When the current in the triac is zero the mains voltage is reapplied across it Synchronization is achieved by measuring this voltage This main voltage is monitored over each halfwave with a network of resistances connected to two I O lines of the ST6210 This allows detection of spurious open load and the retriggering of the triac with multipulse operation if it is not latched after the first gate pulse Operation with a transformer Low power halogen spots use low voltage lamps 12V typ usually supplied through a low voltage transformer Dimming these lamps is simple with this circuit thanks to the program fea tures included in the ST6210 At the start the delay time between the first gate pulse and the synchronization instant is greater than 5ms This limits induction in the transformer
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