View AN2747_9010643.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

may 2008 rev 1 1/44 AN2747 application note 250 w hid metal halide electronic ballast introduction this application note describes the two stages of electronic ballast for a 250 w hid metal halide lamp. the ballast is composed of a boost converter (power factor controller pfc) working in fixed off time and an inverter composed of a full bridge that drives the lamp at low frequency square wave. this design was realized thanks to the very large stmicroelectronics product portfolio. the components include a pfc driver, half-bridge driv ers, a microcontroller, an auxiliary power supply, a voltage reference, logic parts, an amplifier, comparators, power devices as power mosfets, igbts, and fast diodes. in the present note special attention has been given to the full bridge stage. the tests have been conducted using a 250 w metal halide lamp hqi - t (osram) and some design criteria are given with test resu lts. in the full bridge sect ion all lamp phases have been analyzed. figure 1. steval-ilh001v1 www.st.com
contents AN2747 2/44 contents 1 lamp description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.1 lamp phases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 1.1.1 ignition phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 1.1.2 warm-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 1.1.3 burn phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2 general circuit descripti on . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.1 block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.2 lamp power management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 3 board description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 3.1 electrical schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 3.2 bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 4 l6385 high-voltage high and low si de driver . . . . . . . . . . . . . . . . . . . . 20 5 st7lite39 microcontroller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 5.1 application pins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 6 auxiliary power supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 7 ts272 high-performance cmos dual operational amplif iers . . . . . . . 28 8 lm119 high-speed dual com parators . . . . . . . . . . . . . . . . . . . . . . . . . . 29 9 74ac00 quad2-input nand gates . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 10 lamp data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 11 pfc section design criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 12 full bridge design criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 12.0.1 inductor design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 12.1 filter capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 12.2 igniter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
AN2747 contents 3/44 12.3 power mosfet selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 12.4 igbt selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 13 experimental results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 13.1 init phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 13.2 lamp ignition phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 13.3 warm-up phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 13.4 burn phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 13.5 pfc run phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 13.6 thermal measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 14 firmware flowchart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 15 references . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 16 revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
list of figures AN2747 4/44 list of figures figure 1. steval-ilh001v1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 figure 2. lamp families . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 figure 3. luminous efficiency of various lamps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 figure 4. hid lamps operation frequency: high pressure sodium lamps - acoustic resonance duty frequency map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 figure 5. hid lamps operation frequency: metal halide lamps - acoustic resonance duty frequency map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 figure 6. instantaneous lamp power with sinusoidal and square waveforms . . . . . . . . . . . . . . . . . . . 7 figure 7. hid warm-up phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 figure 8. 250 w hid lamp ballast - block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 figure 9. inductor current during charge phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 figure 10. inductor current during discharge phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 0 figure 11. pfc electrical schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 figure 12. full bridge electrical schematic. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 figure 13. control board electrical schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 figure 14. power board layout (not to scale) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 figure 15. control board layout (not to scale) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 figure 16. l6385 block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 figure 17. st7flit3xb general block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1 figure 18. st7flite39 pinout. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 figure 19. mu reference voltage circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 figure 20. pin usage and reset circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 figure 21. vbus measurement circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 figure 22. lamp voltage sensing circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 figure 23. lamp voltage measurement circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 figure 24. constant current control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 figure 25. rsense circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 figure 26. current regulation circuit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 figure 27. auxiliary power supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 figure 28. pinout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 figure 29. lm119 pinout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 figure 30. 74ac00 pinout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 figure 31. eye sensitivity versus frequency. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 figure 32. igniter circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 figure 33. full bridge init phase. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 figure 34. lamp ignition voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 figure 35. lamp current and voltage during warm-up phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 figure 36. warm-up phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 figure 37. steady state phase: lamp current, voltage and lamp power . . . . . . . . . . . . . . . . . . . . . . . . 39 figure 38. steady state phase: lamp current, voltage and lamp power . . . . . . . . . . . . . . . . . . . . . . . . 39 figure 39. ballast efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 figure 40. firmware flowchart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
AN2747 lamp description 5/44 1 lamp description new products and devices are being launched in lighting applications and new solutions for these applications are required. high intensity discharge (hid) lamps have become attractive lighting sources for their luminous efficacy and their long life. figure 2 illustrates the families of electric lighting for which hid lamps are intended. figure 2. lamp families in this document we will refer to high pressu re sodium and mercury lamps as hid lamps. figure 3 shows the luminous efficiency for each lamp type. figure 3. luminous efficiency of various lamps h h i i d d c c f f l l / / t t l l lamp s incande s cent halogen conventional ga s -di s charge mercury low pre ss ure high pre ss ure hb led s s odium
lamp description AN2747 6/44 referring to figure 3 we can see that hid lamps have higher luminous efficacy, but some negative aspects must be considered. when comparing hid and fluorescent lamps, two important issues should be considered: a greater starting voltage and the presence of acoustic resonance. to solve the issue of higher hid ignition voltage, a sort of starting aid, called igniters, are used to ignite the lamp. the problem of acoustic resonance is more comp lex. acoustic resonance is characteristic of hid lamps operating at frequencies greater than 1 khz and appears when lamp power fluctuation exceeds a threshold value. the current/voltage lamp waveforms and the operating frequency cannot be chosen freely, but they are dependent on lamp type, condition and temperature. a wrong choice of frequency and/or waveform can have a very negative effect on lamp performance and/or lifetime and sometimes the discharge tube may be mechanically damaged. as shown in figure 4 and 5 for different lamps the free bands are completely different. for hid lamps the solution proposed to avoid acoustic resonance uses the same principle. the designer must avoid a combination of power fluctuation and operating frequency . another parameter that must be taken into account is flickering. for this reason, the frequency used in the application is higher than 100 hz and below 1 khz. for sinusoidal waveforms the instant lamp power is variable and it has twice the frequency of the voltage and current frequency. in figure 6 a diagram of instantaneous power for different waveforms is shown. figure 4. hid lamps operation frequency: high pressure sodium lamps - acoustic resonance duty frequency map figure 5. hid lamps operation frequency: metal halide lamps - acoustic resonance duty frequency map stable unstable fre q uenc y ~1mhz ~1khz stable unstable fre q uenc y ~1mhz ~1khz
AN2747 lamp description 7/44 figure 6. instantaneous lamp power with sinusoidal and square waveforms for ideal square waveforms, the instant power delivered to the lamp is constant and not modulated by any frequency. this driving plus the low frequency driv ing allows obtaining a system that is immune to the problem of acoustic resonance. for this reason hid lamp applications using square wave current techniques are the best solution. 1.1 lamp phases 1.1.1 ignition phase the ignition voltage for hid lamps is higher with respect to the mains voltage. the peak voltage value to initiate the discharge is very high. typically this is about 3 kv 5 kv. the voltage level at which an hid lamp ignites is called "ignition voltage". this voltage level is referred to the lamp when it is cold bu t this value increases with lamp temperature. to ensure immediate hid lamp restart, called ?hot restrike?, very high re-ignition peaks are necessary (about 20 kv). standard luminaries are not designed for hot restrike voltages. for this reason in order to obtain hot lamp re-ignition, several minutes must elapse for the lamp to cool. the restart time depends on lamp temperature. 1.1.2 warm-up when the discharge has been initiated by the starting gas and the lamp still does not burn properly, a warm-up time is required. during the warm-up time the gas temperature increases, increasing the light output. the lamp voltage starts approximately from a quarter of v lamp and increases up to v lamp . instantaneous power voltage current instantaneous power voltage current
lamp description AN2747 8/44 during this phase the maximum current must be limited and maintained at a value higher than 30% of the nominal value. the time to reach 80% of full light/power is called ?warm-up time?. hid lamps have a warm-up time of approximately 2-5 minutes. in figure 7 typical behaviors of lamp voltage and current during warm-up is shown. figure 7. hid warm-up phase 1.1.3 burn phase after the warm-up phase when the lamp reaches nominal power, the lamp current must be regulated taking into account the lamp voltage to ensure fixed rated power.
AN2747 general circuit description 9/44 2 general circuit description 2.1 block diagram the block diagram of the ballast is shown in figure 8 . the complete circuit is composed of two stages: the boost converter which regulates the output voltage and performs the power factor correction. the inverter stage composed of a full bridge that converts the dc current coming from the pfc stage into an ac current for the lamp. the operation mode of the full bridge realizes a synchronous buck converter. the full bridge moreover drives the igniter block to generate the high-voltage pulses. figure 8. 250 w hid lamp ballast - block diagram to generate a square wave current in the lamp, the circuit is driven in the following way: a) when low side device l2 is switched on, the high side power mosfet h1 operates with a high-frequency pulse wid th modulation (pwm). the duty cycle d is established by a constant-current control circuit. figure 9. inductor current during charge phase in this condition the current increases linearly and the voltage across the inductor l is: viper12 l6385 l6385 stgf10nb60sd main stf12nm50n stp20nm50fd st7flite39 74ac00 lm119 ts272i le50ab lamp filter + bridge l6562 igniter stth8r06dirg lamp h2 h1 l2 l1 dc bus on on l i
general circuit description AN2747 10/44 equation 1 where v l = lamp voltage v dc = dc bus voltage v lamp = lamp voltage b) when the high side device h1 is switched off, the current flows in the low side devices. the freewheeling diode integrated in the low side device igbt l1 operates at high frequency with duty cycle 1-d (see figure 10 ). figure 10. inductor current during discharge phase the voltage across the inductor is: equation 2 the current through l decreases linearly. this circuit is actually a synchronous rectifier buck converter. to minimize the current ripple through the lamp, the circuit operates in continuous conduction mode (ccm) with fixed frequency. the circuit operates in mode a and b complementarily in low frequency supplying the lamp with square wave alternate current. 2.2 lamp power management the lamp power is obtained by multiplying the lamp voltage signal and the lamp current. the lamp voltage is sensed directly across the lamp while the lamp current is obtained using the relation given below. in continuous mode the lamp current is coincident with average buck coil current. starting from peak inductor current the average value is: equation 3 v l v dc v lamp ? = lamp h2 h1 l2 l1 dc bus off on i l v l v lamp ? = i lamp i av i peak i ? 2 ---- - ? = =
AN2747 general circuit description 11/44 where i lamp = lamp current i av = average current i peak = inductor peak current ? i = inductor current ripple the ripple current in a buck converter working in continuous mode is expressed as: equation 4 where v bus = dc bus voltage l= inductance value f= switching frequency = duty cycle for the buck in continuous mode the duty cycle relation is: equation 5 using the relation ( equation 4 ) in the equation ( 5 ) we obtain: equation 6 assuming v bus and f constant it is possible to write: equation 7 the relation ( equation 3 ) can be written as: equation 8 this relation is valid because the average current is equal to the lamp current. this formula is implemented in the microcontroller in order to calculate the lamp current. i ? v bus fl ? ----------- - 1 ? () ?? = v lamp v bus -------------- - = i ? 2 ---- - 1 2flv bus ?? ? --------------------------------- - v lamp v bus v lamp ? () ?? = k 1 2flv bus ?? ? --------------------------------- - = i lamp i peak kv lamp v bus v lamp ? () ?? ? =
board description AN2747 12/44 3 board description the detailed electrical schematics are given in the following figures. 3.1 electrical schematic figure 11. pfc electrical schematic
AN2747 board description 13/44 figure 12. full bridge electrical schematic
board description AN2747 14/44 figure 13. control board electrical schematic
AN2747 board description 15/44 figure 14. power board layout (not to scale) figure 15. control board layout (not to scale)
board description AN2747 16/44 3.2 bill of material table 1. pfc bill of material name value rated type c1 1 f 400 v polyester capacitor c2 10 nf 50 v ceramic c5 1 f 50 v ceramic c6 330 pf 50 v ceramic c7 560 pf 50 v ceramic c8 470 nf 630 v epcos b32523q8474k c9 220 f 450 v epcos electrolytic capacitor b43504-b5227-m7 c10 330 pf 50 v ceramic c11 22 nf 50 v ceramic c12 47 f 35 v electrolytic c13 100 nf 50 v ceramic c14 10 f 50 v electrolytic cx1, cx2 330 nf 275 v epcos x2 capacitor b32922a2334k d2, d3, d4, d13 200 ma 100 v signal diode d5a 3 a, 600 v general purpose rectifier d6 stth8r06dirg stmicroelectronics d8 8 a 1000 v bridge rectifiers d9 zener diode 15 v 1/2 w d10 stth1l06 1 a, 600 v stmicroelectronics d11 stth1l06 1 a, 600 v stmicroelectronics d13 1n4148 f1 fuse 250 v 8 a l1 2 x 6.8 mh 4 a 250 v epcos common mode chokes b82725-j2402-n20 l2 550 h 4 a magnetica part number 1555.0009 l3 2.2 mh m1,m2 stf12nm50n st microelectronics ntc1 s237 epcos b57237s0259m r1 330 ? 1% 1/4 w r2a r2b 680 k ? 1% 1/4 w r3 10 k ? 1% 1/4 w
AN2747 board description 17/44 r5 6.8 k ? 1% 1/4 w r6 6.8 ? 1% 1/4 w r7a,r7b,r7c,r7d 0.68 ? 1% 1/4 w r8 1.5 k ? 1% 1/4 w r9 12 k ? 1% 1/4 w r10a 470 k ? 1% 1/4 w r10b 560 k ? 1% 1/4 w r11 6.8 k ? 1% 1/4w r12 12 k ? 1% 1/4 w r13 6.8 ? 1% 1/4 w tr1 bc557 to92 u1 l6562 stmicroelectronics u2 viper12as-e stmicroelectronics table 2. full bridge bill of material name value rated type c100,c101 100 pf 630 v c102, c103 10 f 25 v c104, c106 3.3 f 50 v epcos polyester capacitor b32529-d5335-k000 c105, c107 33 pf 50 v ceramic c108,c109 68 pf 50 v ceramic c110 100 nf 400 v epcos b32652a6104k c111 680 nf 630 v epcos b32523q8684k c112 220 pf 6 kv murata decb33j221kc4b c113,c114,c115 68 pf 50 v ceramic d100,d101,d102,d103 200 ma 100 v signal diode d104,d105 stth1l06 stmicroelectronics l100 800 h 3.5 a magnetica part number 1775.0001, vogt: sl0607112101 q100,q102 stp20nm50fd stmicroelectronics q101, q104 stgf10nb60s d stmicroelectronics r102 470 m ? 1% 2 w r103 820 k ? 1% 1/4 w r104,r106,r108, r110 100 ? 1% 1/4 w table 1. pfc bill of material (continued) name value rated type
board description AN2747 18/44 r105, r109 22 ? 1% 1/4 w r111 820 k ? 1% 1/4 w r112, r115 10 k ? 1% 1/4 w r113 15 k ? 3 w r114, r116 47 k ? 1% 1/4 w r117, r118 1 m ? 1% 1/4 w t100 high voltage transformer n1/n2=55/3 vogt part number sl0607111102 u100 spark gap 235 v epcos b88069x4290t502 u101, u102 l6385 stmicroelectronics z1,z2 zener diode 16 v 1/2 w table 3. control board bill of material name pos rated type c2 100 nf smd 1206 c3 10 f 15v through hole c4 100 nf smd 1206 c5,c8,c9 0.1 f smd 1206 c6 0.47 f smd 1206 c7 2.2 f smd 1206 c11 22 pf smd 1206 c17, c18 1 nf smd 1206 c19,c20 1 f smd 1206 d1,d2 bat42 stmicroelectronics ld2 green led smd 1206 ld3 red led smd 1206 r2 47 k ? smd 1206 r5,r6 100 k ? smd 1206 r7 5.6 k ? smd 1206 r9 4.7 k ? smd 1206 r10,r15,r20 1 k ? smd 1206 r11,r12 10 ? smd 1206 r3,r4,r8,r14,r17, r18,r19,r21,r22, r26 10 k ? smd 1206 r23,r27 470 ? smd 1206 table 2. full bridge bill of material (continued) name value rated type
AN2747 board description 19/44 r24 r25 u1,u2 74ac00 stmicroelectronics u3 lm119 stmicroelectronics u4 ts272 stmicroelectronics u5 stf7lite39b stmicroelectronics u6 le50-cd 5 v 100 ma stmicroelectronics v1 100 k ? table 3. control board bill of material (continued) name pos rated type
l6385 high-voltage high and low side driver AN2747 20/44 4 l6385 high-voltage high and low side driver figure 16. l6385 block diagram the l6385 is a high-voltage device, manufactured with bcd "off-line" technology. it has a driver structure that enables to drive independently referenced n-channel power mosfets or igbts. the upper (floating) section is enabled to work with voltage rail up to 600 v. the logic inputs are cmos/ttl comp atible for easy interfacing with controlling devices. the main characteristic of this driver are: high-voltage rail up to 600 v dv/dt immunity 50 v/nsec in full temperature range driver current capability: 400 ma source, 650 ma sink switching times 50/30 nsec rise/fall with 1 nf load cmos/ttl schmitt trigger inputs with hysteresis and pull-down undervoltage lockout on lower and upper driving sections internal bootstrap diode outputs in phase with inputs
AN2747 st7lite39 microcontroller 21/44 5 st7lite39 microcontroller the st7lite3 is a member of the st7 microcontroller family of products. all st7s are based on a common 8-bit core, able to run up to 8 mhz clock frequency. enhanced instructions like an 8x8-bit unsigned multiplication and indirect addressing allow good efficiency and a compact application code. figure 17. st7flit3xb general block diagram the mcu main characteristics are: internal rc oscillator with 1% precision at 8 mhz cpu frequency seven input channels 10-bit resolution a/d converter with 3.5 s of conversion time two 8-bit lite timers with prescaler two12-bit auto-reload timers with 4 independent pwm outputs and programmable dead time generation 8 kbytes flash program memory 384 bytes ram 256 bytes data eeprom spi and sci communication interfaces figure 18 shows the st7flite39 pinout.
st7lite39 microcontroller AN2747 22/44 figure 18. st7flite39 pinout 5.1 application pins pin 1: gnd pin 2: vdd: main supply voltage. power is supplied using an stmicroelectronics le50 which is able to supply 5 v with 1% tolerance. figure 19 shows the adopted circuit. figure 19. mu reference voltage circuit
AN2747 st7lite39 microcontroller 23/44 pin 3: reset pin figure 20. pin usage and reset circuit pin 4: adc channel 0 analog input, to measure the main dc bus voltage (vbus). a resistor partition is used to obtain, starting from a +400 v of bus a maximum of 5 v, compatible with the mcu voltage input, see figure 23 . figure 21. v bus measurement circuit pin 5: adc analog input 1: not used pin 6: adc analog input 2: this pin is used to measure the lamp voltage. in figure 23 there are two nets. the first one is a partitioning circuit composed of resistors r118- r114, the other one composed of r117-r116. the voltage across the capacitors c114 and c115 is used as input of u4a to obtain a signal compatible with the mcu input.
st7lite39 microcontroller AN2747 24/44 figure 22. lamp voltage sensing circuit figure 23. lamp voltage measurement circuit pin 7: pb3 digital floating input with interr upt. this pin is used for maximum current protection. pin 8: pb4 digital floating input. it is used for mcu v ref calibration. pin 9: push-pull output, used to drive two status leds. a green led indicates the normal status. a red led indicates a fault condition (for example overcurrent protection). pin 10: sci rxd, used for external communication, power line modem or pc pin 11: sci txd, used for external communication, power line modem or pc pin 12-13: pa6-pa5 not used pin 14: pa4 output pwm3. it is used to generate a reference voltage for the constant current control. the current signal is obtained through a sense resistor r102 (i lamp signal figure 25 ). this voltage across r102 is amplified by u4b st microelectronics amplif ier ts272 and it is compared using the comparator lm119 with the reference voltage coming from the mcu. when the i lamp signal exceeds the defined threshold, the comparator output falls, giving the reset signal to the drivers.
AN2747 st7lite39 microcontroller 25/44 figure 24. constant current control figure 25. r sense circuit pin 15-16: pa3-pa2 output pwm1 and pwm0. these signals are connected to two flip- flops realized using u1 and u2. these flip-fl ops are used to obtain the drive signal for the high side switches, see figure 25 . the set signal is obtained by pwm rising edge, directly from the signal pwm1 and pwm0. this signal is generated at 40 khz fixed frequency. the reset signal is obtained by the output comparator u3. in this way it is possible to generate a pwm signal for drivers with fixed frequency and controlled duty cycle. since the system works in continuous conduction mode to av oid instability in the current control circuit, the maximum duty cycle is limited at 50%.
st7lite39 microcontroller AN2747 26/44 figure 26. current regulation circuit pin 17-18: pa1-pa0 push-pull outputs. these generate the signals for the low side driver. they are directly connected to the l6385 low_side_input pins. pin 19-20: osc2-osc1 external quartz input: not used.
AN2747 auxiliary power supply 27/44 6 auxiliary power supply the proposed power supply can be successfully applied in applications requiring 15 v for the power switch gate driver. this circuit assures good performance in terms of size and performance at very low cost. it is based on the viper12a-e in nonisolated buck configuration. figure 27 shows the schematic. figure 27. auxiliary power supply the viper12a-e is a low-cost smart power device with an integrated pwm controller that is suitable for such applications.
ts272 high-performance cmos dual operational amplifiers AN2747 28/44 7 ts272 high-performance cmos dual operational amplifiers the ts272 devices are low cost, dual operational amplifiers designed to operate with single or dual supplies. these operational amplif iers use the st silicon gate cmos process allowing an excellent consumption-speed ratio. these series are ideally suited for low- consumption applications. figure 28. pinout the main characteristics of this device are: output voltage can swing to ground excellent phase margin on capacitive loads gain bandwidth product: 3.5 mhz stable and low offset voltage three input offset voltage selections
AN2747 lm119 high-speed dual comparators 29/44 8 lm119 high-speed dual comparators these products are precision high - speed dual comparators designed to operate over a wide range of supply voltages down to a single 5 v logic supply and ground and have low input currents and high gains. although designed primarily for applications requiring operation from digital logic supplies, the comparators are fully specified for power supplies up to 15 v. figure 29. lm119 pinout the main characteristics of this device are: two independent comparators supply voltage: +5 v to 15 v typically 80 ns response time at 15 v minimum fan-out of 2 on each side maximum input current of 1 a over operating temperature range inputs and outputs can be isolated from system ground high common-mode slew rate
74ac00 quad2-input nand gates AN2747 30/44 9 74ac00 quad2-input nand gates the 74ac00 is an advanced high-speed cmos quad 2-input nand gate fabricated with sub-micron silicon gate and doub le-layer metal wiring c2mo s technology. the internal circuit is composed of 3 stages including buff er output, which enables high noise immunity and stable output. all inputs and outputs are eq uipped with protection circuits against static discharge, giving them 2 kv esd immunity and transient excess voltage. figure 30 shows the device pinout. figure 30. 74ac00 pinout the main characteristics are: high speed: t pd = 4 ns (typ.) at v cc = 5 v low-power dissipation: i cc = 2 ma (max) at t a = 25 c high noise immunity: vnih = vnil = 28 % v cc (min.) 50 w transmission lin e driving capability symmetrical output impedance: |ioh| = iol = 24 ma (min.) balanced propagation delays: t plh at t phl operating voltage range: v cc (opr) = 2 v to 6 v pin and function compatible with 74 series 00 improved latch-up immunity
AN2747 lamp data 31/44 10 lamp data the lamp data are given below and each is valid for the corresponding operating phase. ignition phase: the ignition voltage in case of a cold lamp is about 4-5 kv. the ignition voltage increases with lamp temperature. the ignition voltage in case of a hot re-strike can reach 25 kv. the circuit is not designed to supply this very high voltage pulse. warm-up phase: during this phase a high warm-up current must be supplied (30% higher than nominal current) to prevent lamp turnoff. the lamp voltage increases gradually starting from a quarter of nominal lamp voltage up to the nominal value. the warm-up time is about 2 minutes. for a 250 w metal halide lamp a current of 3.2 amps is applied. burn phase: the lamp is designed to be driven with a low frequency square wave ac current to avoid acoustic resonance of th e electric arc. acoustic resonance occurs approximately in the frequency domain: 1 khz - 1 mhz. some frequency ranges free of acoustic resonance exist. the commutating frequency of the full bridge should be limited to the domain: 50 hz - 10 khz to avoid any risk of acoustic resonance. in this application the commutating frequency of 160 hz has been chosen. this frequency has been chosen in order to avoid a flickering effect. for frequencies higher than 130 hz eye sensitivity is practically zero. in figure 31 a diagram of eye sensitivity is shown. figure 31. eye sensitivity versus frequency the nominal lamp voltage is approximately 100 v and the nominal lamp power is 250 w. the differential resistance of the lamp is small and negative. to obtain a stable operating point, impedance in series with the lamp is needed.
pfc section design criteria AN2747 32/44 11 pfc section design criteria for pfc design criteria see an 1875. 12 full bridge design criteria the design of full bridge section involves the inductor (buck) component and device selection. 12.0.1 inductor design the design specs are: 1. lamp current 2. lamp ripple current 3. lamp voltage 4. lamp ripple voltage the design steps are summarized below: 1. fix the switching frequency f s and consequently the period t s also is fixed. this frequency for power application is in the range 20 khz 100 khz 2. fix the duty cycle estimation as 3. fix the current ripple in the inductor l 4. calculate the inductance value using the relation: equation 9 for the inductance calculation: f s = 40 khz, t s = 25 s v lamp =100 v v bus = 400 v = 0.25 ? i = 2 a using these parameters the inductance value is 0.93 mh. for this project an inductance of 0.8 mh is used. 12.1 filter capacitor to calculate the capacitor value that is in parallel to the lamp, the max current lamp ripple must be considered. the lamp current ripple must be limited in order to avoid acoustic resonance. in this application the current ripple was fixed at ? i lamp 5% of nominal current v out v input --------------- v lamp v bus -------------- - = = l v lamp 1 ? () t s ?? i ? ----------------------------------------------- =
AN2747 full bridge design criteria 33/44 equation 10 where r lamp can be obtained by the relation (in the hypothesis of linear value): equation 11 substituting this relation in the previous relation it is possible to obtain v lamp .the relation to calculate the output capacitor is: equation 12 ? i= inductor current ripple = 2 a in this case we have: i lamp =2.5 a ? i lamp = 5% i lamp = 125 ma = 250 ma r lamp = 40 ? ? v lamp = 10v c= 625 nf. a capacitor of 680 nf 400 v was selected. 12.2 igniter for the design of the igniter the maximum ignition voltage must be considered. this ignition voltage is obtained by charging a capacitor (100 nf) using a resistor. when the voltage exceeds the gas spark gap threshold (235 v) capacitor is discharged in the primary winding of the high voltage transformer. this voltage is transferred at the secondary winding and a high voltage pulse is obtained, see figure 32 . figure 32. igniter circuit v lamp ? r lamp i lamp ? ? = r lamp v 2 lamp p lamp ----------------- - = c i ? 8f s v lamp ? ?? ----------------------------------- = v > 235v
full bridge design criteria AN2747 34/44 12.3 power mosfet selection for the selection of the power mosfet, the following rules must be considered: v dss > v out ?i d > i t(pk) ?v bus = 400 v ?i t(peak) = 4 a v dss greater than 20% of v bus that is 480 v the stp20nm50fd, fdmesh? power mosfet was selected because it satisfies the following specifications: v dss : 500 v r ds(on) : < 0.25 ? i d : 20 a this device was selected considering the losses in these devices which are are composed of three parts: switch-on, conduction and switch-off losses. the first loss is caused by the voltage across the mosfet at switch-on, the second one depends on r ds(on) and rms current, and the last one is caused by the current at switch- off. the general formulas for conduction and switch-off losses are given below: equation 13 equation 14 12.4 igbt selection considering the current level and the working frequency (160 hz) the best choice for the low side device is the igbt device. in parallel at this power switch the freewheeling diode works at high frequency in continuous conduction mode. since the diode is stressed with high di/dt, t rr , q rr , and i rms became key parameters especially when power loss must be minimized. for both reasons the stgf10nb60sd is the right choice for this application. using high voltage technology based on a patented strip layout, stmicroelectronics has designed an advanced family of igbts, the powermesh? igbts, with outstanding performances. the suffix "s" identifies a family optimized with minimum on-voltage drop for low frequency applications (<1 khz). v ces : 600 v v cesat(max) : < 1.8 v i d : 10 a moreover in the same package a fast diode is integrated with the following characteristics: t rr(typ) : 50 ns q rr(typ) : 70 nc p cond i 2 rms rds on () ?? = p turn off ? v bus i rms t cross f ?? ? =
AN2747 full bridge design criteria 35/44 the power losses can be divided in two quantities: igbt losses and diode losses. the igbt power losses are mainly due to the conduction phase and depend on v cesat . equation 15 in the diode the conduction losses (considering a duty cycle of 50%) can be estimated using the following formula: equation 16 where: p dcond = diode conduction losses i f(av) = average forward current i f(rms) = rms forward current p igbtcond v ce i fav () ? = p dcond v to i fav () rd i 2 frms () ? + ? =
experimental results AN2747 36/44 13 experimental results these results have been obtained at a rated input voltage of 230 v. ambient temperature: 23 c. in the full bridge section the following phases have been analyzed: 1. init phase 2. ignition phase 3. warm-up phase 4. steady state phase 13.1 init phase during this phase the dc bus voltage is sensed and both low side devices are switched on. in this way both bootstrap capacitors are charged. the init phase is shown below in figure 33 . figure 33. full bridge init phase c1 = low side igbt 1 gate voltage c2 = low side igbt 2 gate voltage c3 = inductor current c4 = lamp voltage
AN2747 experimental results 37/44 13.2 lamp ignition phase the high voltage transformer generates a proper ignition voltage to ignite the lamp. the voltage across the lamp is shown below in figure 34 . figure 34. lamp ignition voltage 13.3 warm-up phase during this phase the lamp current is limited and the lamp voltage increases starting from a quarter of nominal voltage until the rated voltage. during this phase the lamp power increases and at 80% of nominal lamp power the control power is activated, regulating the lamp power.
experimental results AN2747 38/44 figure 35. lamp current and voltage during warm-up phase c2 = lamp current c3 = inductor current c4 = lamp voltage figure 36. warm-up phase 13.4 burn phase during this phase the lamp is supplied with low-frequency square wave current. the lamp current and the lamp power are maintained constant and some waveforms are shown in figure 37 and 38 .
AN2747 experimental results 39/44 figure 37. steady state phase: lamp current, voltage and lamp power figure 38. steady state phase: lamp current, voltage and lamp power 13.5 pfc run phase during the run phase the input power the power factor and the input current thd have been measured. the results are given in ta bl e 4 .
firmware flowchart AN2747 40/44 below figure 39 shows a diagram of total ballast effi ciency versus input voltage. the system efficiency is obtained as a ratio of lamp power to input power. figure 39. ballast efficiency 13.6 thermal measurement in the output stage a thermal measurement on the power device has been performed. on the devices a heat sink having thermal resistance r th = 3.23 c/w has been mounted. the temperature was measured on the top of the packages of the power devices by means of a thermocouple. a ? t of 55 c above ambient temperature has been measured. 14 firmware flowchart a simplified firmware flowchart is given in figure 40 . table 4. power factor and input current thd measurements vin (rms) v power factor thd% 115 0.994 10 230 0.940 27
AN2747 firmware flowchart 41/44 figure 40. firmware flowchart
references AN2747 42/44 15 references 1. "design of fixed-off-time controlled pfc preregulators with the l6562" (an1792) 2. "eval6562-375w, 375 w fot-controlled pfc pre-regulator with the l6562 (an1895) 3. "l6562-250w high performance tm pfc" 4. "l6562 transition-mode pfc controller" (datasheet) 5. "stf12nm50 n-channel 500 v 0.29 ? 11a mdmesh power mosfet" (datasheet) 6. "stth8r06dt turbo 2 ultrafast high voltage rectifier" (datasheet) 7. "l6385 high-voltage high and low side driver" (datasheet) 8. "stf20nm50 n-channel 500 v 0.29 ? 11a mdmesh power mosfet" (datasheet) 9. "stgp10nb60s n-channel 10 a 600 v powermesh igbt" (datasheet) 10. "viper12 low power off-line smps primary switcher" (datasheet) 11. "st7flite39 8-bit mcu with single voltage flash, data eeprom, adc, timers, spi, linsci" (datasheet) 12. "74ac00 quad 2-input nand gate" (datasheet) 13. "lm119 high speed dual comparators" (datasheet) 14. "ts272i high performance cmos dual operational amplifiers" (datasheet) 15. "le50ab very low drop voltage regulators with inhibit" (datasheet)
AN2747 revision history 43/44 16 revision history table 5. document revision history date revision changes 06-may-2008 1 initial release
AN2747 44/44 please read carefully: information in this document is provided solely in connection with st products. stmicroelectronics nv and its subsidiaries (?st ?) reserve the right to make changes, corrections, modifications or improvements, to this document, and the products and services described he rein at any time, without notice. all st products are sold pursuant to st?s terms and conditions of sale. purchasers are solely responsible for the choice, selection and use of the st products and services described herein, and st as sumes no liability whatsoever relating to the choice, selection or use of the st products and services described herein. no license, express or implied, by estoppel or otherwise, to any intellectual property rights is granted under this document. i f any part of this document refers to any third party products or services it shall not be deemed a license grant by st for the use of such third party products or services, or any intellectual property contained therein or considered as a warranty covering the use in any manner whatsoev er of such third party products or services or any intellectual property contained therein. unless otherwise set forth in st?s terms and conditions of sale st disclaims any express or implied warranty with respect to the use and/or sale of st products including without limitation implied warranties of merchantability, fitness for a parti cular purpose (and their equivalents under the laws of any jurisdiction), or infringement of any patent, copyright or other intellectual property right. unless expressly approved in writing by an authorized st representative, st products are not recommended, authorized or warranted for use in milita ry, air craft, space, life saving, or life sustaining applications, nor in products or systems where failure or malfunction may result in personal injury, death, or severe property or environmental damage. st products which are not specified as "automotive grade" may only be used in automotive applications at user?s own risk. resale of st products with provisions different from the statements and/or technical features set forth in this document shall immediately void any warranty granted by st for the st product or service described herein and shall not create or extend in any manner whatsoev er, any liability of st. st and the st logo are trademarks or registered trademarks of st in various countries. information in this document supersedes and replaces all information previously supplied. the st logo is a registered trademark of stmicroelectronics. all other names are the property of their respective owners. ? 2008 stmicroelectronics - all rights reserved stmicroelectronics group of companies australia - belgium - brazil - canada - china - czech republic - finland - france - germany - hong kong - india - israel - ital y - japan - malaysia - malta - morocco - singapore - spain - sweden - switzerland - united kingdom - united states of america www.st.com

▲Up To Search▲

Price & Availability of AN2747

	To Download AN2747 Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .