INTRODUCTION last years, triacs spread areas electronics, including do

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INTRODUCTION last years, triacs spread areas electronics, including do

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IMPROVEMENT TRIAC COMMUTATION
INTRODUCTION last years, triacs spread areas electronics, including domestic appliances industrial applications. triacs been traditionally limited their switching behavior applications where there risk spontaneous firing after conduction. order obtain required reliability today's equipment, designer must take certain number precautions: over dimensioning device, switching networks (snubber), significant margin security junction temperature, etc. This generally involves additional costs. After brief discussion commutation problem when triac turned off, this article will describe progress made this area newest possibilities offered triac user thanks series Logic Level SNUBBERLESStriac. commutation problem triac electrical representation triac compared thyristors mounted anti-parallel coupled with control device which allows activation this switch with only gate (see Figure 1a). considering structure triac (see Figure 1b), notices that conduction zones, corresponding these thyristors which control current direction then other, narrowly overlap each other control zone. During conduction time, certain quantity charges injected into structure. biggest part these charges disappears recombining during fall current circuit, while another part extracted moment blocking inverse recovery current. Nonetheless excess charge remains, particularly neighboring regions gate, which provoke certain cases firing other conduction zone moment when supply voltage circuit reapplied across triac. This problem commutation. given structure determined junction temperature, switching behavior depends quantity charges which remains moment when current drops zero. this number charges linked value current which circulating triac approximately microseconds before cut-off. (This time corresponds three times life time minority carriers). Thus, parameter consider here will slope decreasing current which called commutating di/dt, (di/dt)c. (see Figure speed which reapplied voltage increases moment when triac turns off, which called commutating dv/dt, (dv/dt)c. (see Figure capacitive current, proportional (dv/ dt)c, flows into structure, therefore injected charges added those coming from previous conduction.
REV. 3577 1/14
Figure Simplified equivalent schematic triac circuit; Example triac structure
CONTROL AREA
Characterization order characterize switching behavior triac when turns off, consider circuit which vary slope decrease current (di/dt)c. addition, control slope reapplied voltage using, example, circuit resistors capacitors connected across triac measured. determined (dv/dt)c, progressively increase (di/dt)c until certain level which provokes spontaneous firing triac. This critical (di/dt)c value. Therefore, different (dv/dt)c values, note critical (di/dt)c value each sample. This makes possible trace curve commutation behavior triac under consideration. Figure represents results obtained with standard triac (IGT 50mA) sensitive gate, triac (IGT 10mA). standard triacs critical (di/dt)c sightly modified when vary (dv/dt)c. sensitive gate triacs, this parameter noticeably decreases when slope reapplied voltage increased.
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Figure Triac voltage current commutation
(Triac current)
(di/dt)c
(Triac voltage)
Voltage conducting state (dv/dt)c
Voltage blocked state
Figure Critical (di/dt)c versus (dv/dt)c (below curve triac turns spontaneously)
(di/dt)c
CRITICAL (dI/dt)c VERSUS (dV/dt)c
(A/ms)
SAMPLE TRIAC
SAMPLE SENSITIVE TRIAC
(dv/dt)c
(V/µs)
Note: rate re-application off-state voltage these points corresponds mains (sinusoidal wave form) zero crossing. (dv/dt)c limited snubber values generally specified data sheets (5V/ms 10V/ms). These points obtained without snubber.
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practice, current waveform, thus (di/dt)c, imposed circuit. Generally cannot change triacs applications always necessary know (di/dt)c circuit order choose triac with suitable critical (di/dt)c. This most important parameter. Suppose circuit which (di/dt)c reaches 15A/ms. triac characterized upper curve Figure suitable such circuit even (dv/dt)c reduced nearly zero connecting huge snubber network across Applications basic circuits When considering constraints commutation turn triac, distinguish cases: triac resistive load (see Figure this case current voltage phase. When triac switches (i.e. when current drops zero), supply voltage nullified this instant will increase across triac according sinusoidal law: sint Example: European mains Vrms 220V 50Hz, slope will
Vrms
This relatively (dv/dt)c corresponds points curves Figure (di/dt)c concerned circuit, depends load. resistance loads under Vrms voltage, will have:
Vrms
triac inductive load. this case there phase between current supply voltage (see Figure When currents drops zero triac turns voltage abruptly pushed terminals. limit speed increasing voltage, generally resistive/capacitive network mounted parallel with triac. This "snubber" calculated limit (dv/dt)c 10V/µs according specified value data sheet. This case corresponds points Figure (di/dt)c also determined this case load impedance supply voltage.
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Figure Current voltage ware forms resistive loads: Case switching; Case phase control)
Gate trigger Gate trigger
Triac
Triac (dI/dt)c
(dI/dt)c
Triac (dV/dt)c
Triac (dV/dt)c
Supply Voltage
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Figure Current voltage ware forms inductance loads: Case switching; Case phase control
Gate trigger Gate trigger
Triac
Triac (dI/dt)c (dI/dt)c
Triac (dV/dt)c
Triac (dV/dt)c
Supply Voltage
triac without snubber network triac thus considered switch which turns moment when current dampened oscillating circuit constituted loads internal capacity triac (see Figure case pure inductive load, maximum reapplied (dv/dt)
Vrms Irms
example, internal capacitance triac about 70pF. Therefore, inductive load, maximum (dv/dt)c without snubber will limited according characteristics load. interesting know behavior triac, particular critical (di/dt)c value, these conditions. This characterization corresponds points curve Figure
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Figure Triac commutation inductance load without snubber network
LOAD LOAD (dV/dt)c
PROGRESS: TECHNOLOGY make significant progress triac area essentially improve commutative behavior turn triac. other words critical (di/dt)c improved. order reach this goal, structure been developed. this structure, different active zones have been de-coupled maximum such separate elementary thyristors gate area. This made possible sacrificing gate triggering fourth quadrant. practice this does pose problem because gate drive circuits triac generally third first quadrants (see Figure Figure Triac commutation inductance load without snubber network
-VCC
DIAC OPTO COUPLEUR (Photo Triac)
given technology, commutative behavior triacs depends sensitivity gate. correlation between critical (di/dt)c gate current triacs represented Figure same chart, results obtained with conventional triacs versus technology triacs. seen, progress that been made this level significant.
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performances specifications Figure Correlation between commutative behavior sensitivity. (Measurements performed several lots triacs)
Critical (dI/dt)c
A/mS
TECHNOLOGY PARTS CONVENTIONAL TRIACS
quadrant (mA)
technology been into place with manufacturing series, Logic Level SNUBBERLESS Triacs. data sheets these triacs critical (di/dt)c limit specified maximum junction temperature max). Logic Level triacs this category consider sensitive triacs which maximum gate current (IGT) type 10mA one. data sheets Logic Level triacs minimum (di/dt)c specified following cases: Resistive load with (dv/dt)c 0.1V/µs. Inductive load with (dv/dt)c 20V/µs example triac specified follows: Table Triac specifications
Suffix Symbol (di/dt)c Test conditions VDRM; 90mA; dIG/dt 0.8A/ms dV/dt 0.1V/ms 110°C dV/dt 20V/ms 25°C Quadrant A/ms Unit
Note: either polarity electrode voltage with reference electrode
SNUBBERLESS Triacs This series triacs presently covers range with gate currents 35mA type) 50mA type) according type required.This series been specially designed that triacs switches from state state without external snubber circuit.
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Whatever nature load, there absolutely risk spurious firing turn triac long functioning under specified (di/dt)c value. SNUBBERLESS triacs specified critical (di/dt)c values which greater than decreasing slope nominal current sinusoidal configuration. example, slope current triac conducting when current drops zero
Irms 7A/ms 50Hz
BTA/BTB16-600BW specified (di/dt)c 14A/ms. Table summarizes characteristics SNUBBERLESS triacs which presently available: Table Characteristics SNUBBERLESS triacs presently available
WITHOUT SNUBBER Type Current Voltage 800V 800V 800V 800V 800V 800V 800V 800V Suffix (mA) Static dV/dt (V/µs) (dI/dt)c (A/ms)
ADVANTAGES APPLICATIONS Logic Level goal these triacs controlled directly logic circuits microcontrollers like series: Outputs sink currents 20mA line, therefore drive These triacs ideal interface power components supplied 220V, such valves, heating resistances, small motors. specification critical (di/dt)c value both resistive inductive loads allows know margin security circuit relation risk spurious firing, which results improved reliability, optimize performance triac used, which results cost reduction.
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Figure Triac commutation inductance load without snubber network
LINE
FUSE 100k 100k 220k MODE
RESET
4.7M
TOUCH SENSOR
08-400SW
ST6210
220k
PUSH BUTTON
TEST OSCOUT OSCIN
220k BZW55C5V6 100µ 6.3V 1N4148
8MHz
POTENTIOMETER
NEUTRAL
220n 400V 1/2W
resistors: 1/4W unless otherwise specified
SNUBBERLESS Triacs commutation SNUBBERLESS triacs specified without limitation (dv/dt)c. With suppression snubber circuit, there noticeable cost reduction. Each SNUBBERLESS triac series specified with critical (di/dt)c value static (dv/dt) highest possible level, taking into consideration gate sensitivity (IGT). minimum specified levels these parameters allows these products circuits where there need high safety factor, such Static relays which load well defined. With conventional triacs difficult adapt snubber possible cases. SNUBBERLESS triacs resolve this problem (see Figure 10). Motor drive circuits. Figure shows inversion circuit asynchronous motor where spurious firing triac, normally assumed off-state, must absolutely avoided. critical (di/dt)c SNUBBERLESS triacs greater than slope nominal current specific type under consideration. This important several applications, including: Circuits which (di/dt)c transient state greater than steady state. This case universal motors controlled phase control circuit. Table shows SNUBBERLESS triac optimize efficiency circuit. Circuits which generate wave forms with very high (di/dt)c, such inductive load supplied diode bridge (see Figure 12). only limited parasitic inductance circuit.
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Figure Solid state relay diagram
INPUT OPTO INSULATED DRIVE CIRCUIT ZERO CROSSING CIRCUIT LOAD LINE
Figure Triac commutation inductance load without snubber network
MOTOR LINE (220 VRMS)
LS+R
GATE DRIVE CIRCUIT
Table Universal motor control: Triac choise must comply with maximum (dI/dt)c (For example, SNUBBERLESS triac sufficient control 110V motor)
Power 1200 Supply Voltage 220V/50Hz 110V/60Hz 220V/50Hz 110V/60Hz Nominal Current ARMS ARMS ARMS ARMS Current Control Triac Range (di/dt)c Max(1) A/ms A/ms A/ms A/ms Standards Triac BTA10-600B BTA16-400B(2) BTA16-600B BTB24-400B SNUBBERLESS Triac BTA06-600BW BTA10-400BW BTA10-600BW BTA20-600BW
Note: Maximum transient (dI/dt)c. This parameter depends very much type motor. This type specified 7A/ms munumum small certain applications could need standard triac.
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Figure Triac commutation inductance load without snubber network
Inductive load (Motor, valve,
CONCLUSION Thanks recent progress made triac technology, designer disposal devices with commutating behavior which compatible with applications 60Hz range. This includes phase control static commutation loads going from watts several kilowatts. capability this generation triacs allows: increase reliability circuits, particularly where there risk spontaneous firing even most difficult configurations. reduce cost using sensitive gate, LOGIC LEVEL triacs without need interface between gate logic circuit, utilizing SNUBBERLESS triacs which specified without resistive/capacitive network. Additionally, limit (di/dt)c parameter listed data sheets. This permits optimization circuit specifying stricter guidelines choice component.
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REVISION HISTORY Table Revision History
Date May-1992 19-Apr-2004 Revision First Issue Stylesheet update. content change. Description Changes
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Information furnished believed accurate reliable. However, STMicroelectronics assumes responsibility consequences such information infringement patents other rights third parties which result from use. license granted implication otherwise under patent patent rights STMicroelectronics. Specifications mentioned this publication subject change without notice. This publication supersedes replaces information previously supplied. STMicroelectronics products authorized critical components life support devices systems without express written approval STMicroelectronics. logo registered trademark STMicroelectronics. other names property their respective owners 2004 STMicroelectronics rights reserved STMicroelectronics GROUP COMPANIES Australia Belgium Brazil Canada China Czech Republic Finland France Germany Hong Kong India Israel Italy Japan Malaysia Malta Morocco Singapore Spain Sweden Switzerland United Kingdom United States www.st.com
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