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dimmable ballast solution
This application note describes dimmable ballast solution which completely replace incandescent lamps formal dimming systems. dimmer controlled range 100% full light output without changing formal triac dimmer. Compared formal solution, this solution only provides energy savings, also higher reliability much longer operating life. solution based high performance ballast driver L6574D, STD4NK50Z Zener protected SuperMESHPower MOSFETs, STTH1L06 turbo ultra fast high voltage rectifiers. Figure Typical dimmer
Figure
Dimming ballast solution
October 2007
1/17
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Contents
AN2590
Contents
Typical dimming system incandescent lamps
Formal ballast disadvantages Proposed solution
Board description
Application circuit Dimming function Principle main circuit Calculations
Electrical specifications reference design board
Electrical specifications layout view
Test results Conclusion
References
Revision history
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AN2590
List figures
List figures
Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Typical dimmer Dimming ballast solution Typical dimming system consisting incandescent lamp triac dimmer Block diagram formal ballast half line cycle sinuous wave firing angle. Schematic reference design board Main circuit current switching period. current shape top-side view bottom-side view Full load efficiency line input Triac turn-on time power dissipation lamp. input voltage current voltage current Power factor operating range Lamp voltage current Ton=9 Vlamp=100 V/div, Ilamp= mA/div. Lamp voltage current Ton=5 Vlamp=100 V/div, Ilamp= mA/div. Lamp voltage current Ton=3 Vlamp=100 V/div, Ilamp= mA/div.
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Typical dimming system incandescent lamps
AN2590
Typical dimming system incandescent lamps
typical dimming system consists lamp(s) dimmer (Figure dimmer consists triac components, Figure Dimmers this type appropriate incandescent lamps very popular market. Figure Typical dimming system consisting incandescent lamp triac dimmer
triac conducts once been triggered holds latching current. triac shuts down when current less than holding current. dimmer works fine with resistive load. triac triggered timing sinuous voltage line input), kept conduction state until reaching zero line voltage. This allows lamp dimmed nearly 100%.
Formal ballast disadvantages
Since formal resistive load, ballast power factor correction circuit (PFC). incandescent lamp (Tungsten filament light bulb) replaced formal (Compact Florescent Lamp) directly, cannot fully illuminate have intermittant blinking light all. Figure shows block diagram formal CFL. Figure Block diagram formal ballast
formal ballast consists rectifier, storage capacitor, ballast driver circuit, half bridge resonant circuit. source energy stored only storage capacitor from input timing nears peak voltage half cycle. When formal ballast connected triac dimmer (see Figure triac conducts only after having been triggered, that when rectified voltage higher than voltage across storage capacitor. this extreme moment capacitor charged with same peak from
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AN2590
Typical dimming system incandescent lamps input, triac then immediately turned off. impossible adjust voltage across storage capacitor then extend triac firing angle less than 90°. However lamp continue flicker remain unstable voltage well managed.
Proposed solution
ballast been developed based L6574D. lamp power dimmed from below 100% (full illumination) adjusting triac dimmer. With implementation solution, lamp power adjusted switching frequency driver circuit that corresponds illumination level triac dimmer. triac triggered every point during half cycle conducts continuously until half cycle (180°). addition, circuit detects firing angle triac adjusts lamp power adjusting switching frequency half bridge control lamp power depending position triac dimmer. Please note that while triac dimmer connected capacitive load (CFL), triac will fired trigger angle lower than 50°. Because voltage (the voltage across storage capacitor) falls, system stops operating angle less than 40°. this reason, dimmable ballast cannot operated full dimming range. hysteretic range half cycle turned turned 40°. Figure shows Gate pulse (trigger) firing angle half cycle. Figure half line cycle sinuous wave firing angle
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Board description
AN2590
Board description
Application circuit
reference design board made according schematic shown Figure includes filter, bridge rectifier, single stage with high frequency ballast driver resonant circuit. Figure Schematic reference design board
DRAFT
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AN2590
Board description
Dimming function
modes dimming function frequency modulation voltage modulation. this solution, dimming function obtained using methods: frequency modulation voltage modulation. When trigger angle triac changes from 90°, only frequency modulation works. When angle changes from 180°, both them work, voltage modulation dominates. Frequency modulation depends operational amplifier L6574D. Figure were used simulate trigger angle triac. When angle changes from 180°, voltage across which positive input amplifier (Pin here number L6574D), decreases accordingly. output (Pin amplifier decreases with negative input (Pin amplifier automatically decreases. equivalent resistance between decreases, switching frequency increases, hence lamp power decreases. angle changes from 180° 360°, lamp power increases. Voltage modulation means that voltage across (see Figure decreases when firing angle triac changes from 180°. This makes lamp power decrease.
Principle main circuit
order simplify analysis, main circuit shown Figure There independent circuits, power factor correction (PFC) circuit half bridge resonant circuit. which labeled (dotted line) consists Cf1, Cf2, Db1, Db2, other half bridge resonant circuit, which labeled (solid line). consists Lamp. Power MOSFETs operate complementarily almost duty ratio. Figure Main circuit
Since switching frequency high enough, voltages across divider capacitors (Cf1&Cf2) treated constant during switching cycle. Thus voltage across always higher than line peak. Figure switching cycle shows model four stage current flow through
7/17
Board description
AN2590
Stage [t0. charge already turned off. Assume current through (iL1) zero, then increases linearly voltage across Cf1, current flows through Cf1, Db1, Stage [t1. discharging turned turned moment reaches positive peak that forces turn negative voltage (Vc1-Vcf1) applied causing decrease linearly. current flows through Cf1, Db1, Stage [t2. charge reaches zero, linearly increases negative peak voltage across Cf2. current flows through Cf2, Db2. Stage [t3. discharging turned turned off. When reaches negative peak that forces turn voltage (Vc1-Vcf2) applied causing decrease linearly. current flows through Cf2, Ds1, Db2. reaches zero, where switching cycle begins. Figure current shape
Figure
current switching period
overall current flow shape during half line cycle shown Figure clear that boost inductor current flows directions circuit works boundary conduction mode.
Calculations
From above analysis, main parameters circuit calculated application. design circuit, inductor (L1) peak current (Ipk) most important. resonant circuit, main parameters. calculation steps given follows:
Step during switching cycle given
Equation
Where input voltage after rectifier, period switching time, discharging time voltage across
8/17
AN2590 consequence that, have following. Equation
4Vc1
Board description
Equation
TsVin 2Vc1
Step input current (Iac) equals half average inductor current divider capacitors,
Equation
16L1 2Vc1
Step input power determined
Equation
Where input voltage. With above three steps, values found input/output conditions switching frequency given.
Step half bridge resonant circuit, equivalent resistance lamp given
Equation
rms, lamp lamp rms, lamp
Where Vrms,lamp rated lamp voltage, Irms,lamp rated lamp current. With Vrms,lamp Irms,lamp input voltage half bridge (Vc1), results easily obtained.
Step MOSFET selection. order select adequate MOSFET parameters V(BR)DSS, RDSON important. V(BR)DSS should selected according with certain safe margin. compact application, thermal issue becomes very critical. Thus RDSON must selected with safe margin also.
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Electrical specifications reference design board
AN2590
Electrical specifications reference design board
Electrical specifications
electrical specifications reference design board shown Table Table Electrical specifications evaluation board(1)
Value Parameter Min. input (operating range) Line frequency Load compact florescent lamp) Rated switching frequency (pin14 L6974D) Minimum dimmable lamp power Maximum dimmable lamp power Lamp power without connection triac dimmer Power factor
test under input V/50 room temperature
Unit Typical 16.6 0.92 Max. 20.75 16.4 19.25
layout view
layout board shown below. Figure shows side view Figure shows bottom side view.
Figure top-side view
Figure bottom-side view
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AN2590
Test results
Test results
evaluation results include ballast system efficiency dimming characteristics performance power factor reference design board addition more typical waveforms evaluation boards. efficiency full load operating input voltage higher than 80%, Figure Figure Full load efficiency line input
triac turn time half cycle relates power dissipation lamp. system operating VAC/50 Hence maximum half cycle time Theoretically, range corresponding firing angle 180°. under real conditions range about Figure Figure Triac turn-on time power dissipation lamp
Figure shows input voltage current maximum turn-on time triac. glitch (circled waveform) always exists each half cycle input voltage. current spike (circled waveform) occurs each half cycle when line voltage reaches peak. Although good power factor, suitable this application ensures that voltage higher than peak input voltage.
11/17
Test results
AN2590
Figure input voltage current
Figure voltage current
Figure shows voltage current waveform boost inductor glitch could happen while works directions critical conduction mode. Although glitch there, limitation maximum Ton, power factor always higher than operating range. Please refer Figure below. Figure Power factor operating range
different triac dimming control circuit provides different power dissipation lamp. figures also show negative resistance characteristics lamp, such when lamp current decreases, voltage increases accordingly. Figure shows voltage current measurement equal Figure shows voltage current measurement equal Figure shows voltage current measurement equal
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AN2590 Figure Lamp voltage current Ton=9 Vlamp=100 V/div, Ilamp= mA/div
Test results
Figure Lamp voltage current Ton=5 Vlamp=100 V/div, Ilamp= mA/div
Figure Lamp voltage current Ton=3 Vlamp=100 V/div, Ilamp= mA/div
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Conclusion
AN2590
Conclusion
dimmable solution been discussed analyzed. CFLs completely replace incandescent lamps dimming systems. With dimming range 20%-100%, CFLs very energy efficient have reliable longer lifetime. efficiency above which makes this solution suitable compact applications.
References
L6574D Datasheet CFL/TL ballast driver preheat dimming AN993, application note electronic ballast with using L6574 L6561
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AN2590
Bill material
Appendix
Table
Symbol Cf1, Db1,
Bill material
Bill material
Value 1N4007 1N4148 STTH1L06 turbo ultra fast high voltage rectifiers, STMicroelectronics Electrolytic ceramic TSL1112-472JR21, Table C3216C0G2J681J, Electrolytic Electrolytic Note
15/17
Revision history Table
Symbol
AN2590 Bill material (continued)
Value STD4NK50Z L6574D Zener protected SuperMESHPower MOSFET, STMicroelectronics high performance ballast driver, STMicroelectronics Note
Table
Specification inductors "L1" "Lr"
item Core Bobbin Winding Used type PC40EE16-Z equivalent BE16-116CPFR AWG34 turns each inductance
Revision history
Table
Date 08-Oct-2007
Document revision history
Revision First release Changes
16/17
AN2590
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AN2590

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