AN2982 Application note 1 x 54 W T5 fluorescent lamp ballast in wide input voltage range using the L6585DE - STEVAL-ILB005V2 Introduction This application note describes the STEVAL-ILB005V2 demonstration board equipped with the L6585DE lighting controller, STD7NM50N MOSFETs and an STTH1L06 Shottky diode able to drive a 54 W linear T5 fluorescent lamp in a wide input voltage range (88 - 277 Vac). The design steps, schematic and board performance are also given. The L6585DE lighting controller embeds both the PFC stage and ballast stage suitable for driving all kinds of lamps (T8, T5, T4, CFLn,...) and all kinds of topologies having an input power greater than 25 W. New T5 lamps are characterized by very high luminous efficiency and compactness. To optimize their performance, high accuracy in both preheating of the cathodes and steadystate parameters is required. The minimum performance of T5 ballasts together with their minimum safety requirements are summarized in international norms, especially IEC613472-3, IEC60929, and IEC60081. The demand for these lamps is rapidly growing and the L6585DE is able to control electronic ballasts meeting all performance specifications and reliability with low component count and a small PCB. The STEVAL-ILB005V2 has been developed to drive a 54 W T5-HO lamp. Figure 1. STEVAL-ILB005V2 demonstration board !-V March 2010 Doc ID 15599 Rev 1 1/31 www.st.com Contents AN2982 Contents 1 2 3 4 2/31 Designing the application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1 Design requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.2 PFC design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.2.1 Output voltage and dynamic OVP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.2.2 Boost choke design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.2.3 MOSFET selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 1.2.4 Boost diode selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 1.2.5 Bulk capacitor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 1.2.6 Multiplier biasing and selection of PFC current sense resistor . . . . . . . 10 1.2.7 Error amplifier compensation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 1.2.8 Input rectifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 1.2.9 Input capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 1.2.10 Input circuitry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Ballast stage design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 2.1 Resonant network and operating point design . . . . . . . . . . . . . . . . . . . . . 15 2.2 Selection of parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 2.3 Half-bridge design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 2.4 End of life detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 2.5 IC power supply design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Demonstration board schematic and bill of material . . . . . . . . . . . . . . 23 3.1 Demonstration board performances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 3.2 Ballast stage performance and reliability . . . . . . . . . . . . . . . . . . . . . . . . . 27 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Doc ID 15599 Rev 1 AN2982 List of figures List of figures Figure 1. Figure 2. Figure 3. Figure 4. Figure 5. Figure 6. Figure 7. Figure 8. Figure 9. Figure 10. Figure 11. Figure 12. Figure 13. Figure 14. Figure 15. Figure 16. Figure 17. Figure 18. Figure 19. Figure 20. Figure 21. Figure 22. Figure 23. Figure 24. STEVAL-ILB005V2 demonstration board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Typical application schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 PFC MOSFET frequencies along mains half period (fmains = 50 Hz) for various input voltages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Summary of PFC MOSFET power losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Multiplier bias points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Control loop block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Bode plot with simple compensation network: |Gloop|MAX < 35dB . . . . . . . . . . . . . . . . . . 12 Bode plot with enhanced compensation network: |Gloop|MAX < 35 dB and F margin > 45° . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Complete EMI filter (differential mode inductors are not present in this design). . . . . . . . . 14 Resonant inverter simplified schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Resonance curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Parameters setting block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Blocking capacitor to ground topology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Charge pump network and startup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 STEVAL-ILB005V2 schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Input performance - power factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Input performance - total harmonic distortion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 EMI spectrum at 277 Vac . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 EMI spectrum at 88 Vac . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Steady-state lamp parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Startup sequence with open lamp protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Ballast anti-choke saturation protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 EOL protection (positive deviation) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 EOL protection (negative deviation) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Doc ID 15599 Rev 1 3/31 Designing the application 1 AN2982 Designing the application The STEVAL-ILB005V2 design follows the AN2870 design guidelines. In this section the design specifications and the equations used are given. 1.1 Design requirements Table 1. Summary of design requirements Description Values Input voltage 88 to 277 Vac (110 to 230 Vac ±20%) Mains frequency 50 Hz – 60 Hz PF > 0.975 Current THD < 10% Lamp type T5 -54 W HO (Ilamp = 460 mArms; Vlamp = 117 Vrms) Max output voltage 900 Vrms Lamp connection Current preheated, Cblock to ground topology Efficiency 90% Figure 2. Typical application schematic 6OUT 4PFC $BOOST 2INVH 2CTRH #OUT 2ECTIFIER "RIDGE 2CP #CP 2CTRL 2INVL #IN 6 # 2ZCD #BOOT #COMP :#$ 6IN 2SU #CTR -PFC ).6 #/-0 6CC #42 -HS "//4 0&' (3$ ,BALLAST 2MULTH 0&##3 ,$% ,AMP /54 -LS -5,4 2MULT #MULT 2PFCS '.$ /3# 2& #OSC 2PRE %/) 4#( %/,0 %/, ("#3 #RES 2EOL 2D 2P #IGN 2RUN ,3$ #D 2EOL 2HBCS #EOL #BLOCK !-V 4/31 Doc ID 15599 Rev 1 AN2982 Designing the application 1.2 PFC design 1.2.1 Output voltage and dynamic OVP The maximum input voltage is equal to: Equation 1 V in,max = 277 V ⋅ 2 = 391.7 V An output voltage equal to Vout = 420 V is chosen for better PFC performance. Choosing Rinvh = 3 x 2.2 MΩ, the output voltage is equal to: Equation 2 ⎛ R Vout = 2.52V ⋅ ⎜⎜1 + invh Rinvl ⎝ ⎞ ⎟⎟ ⎠ → Rinvl = Rinvh = 39839 Ω → R invi = 39.7 kΩ ⎛ Vout ⎞ − 1⎟ ⎜ ⎝ 2.52V ⎠ The ripple superimposed on Vout is chosen equal to 5%. Then, the maximum instantaneous output voltage is equal to 441 V and, therefore, the OVP level must be comprised between 450 V and 500 V. – VOVP = 480 V is chosen and the CTR pin voltage divider is dimensioned accordingly – Rctrh = 3 x 825 kΩ Equation 3 ⎛ R ⎞ R ctrh VOVP = 3.4 V ⋅ ⎜⎜1 + ctrh ⎟⎟ → R ctrl = = 17656 Ω → R invi = 18 kΩ V R ⎛ ⎞ OUT,MAX ctrl ⎠ ⎝ ⎜⎜ − 1⎟⎟ ⎝ 3 .4 V ⎠ 1.2.2 Boost choke design The minimum PFC frequency is chosen equal to fPFC,min > 15 kHz. The maximum inductance value is equal to: Equation 4 fPFC,min = ⎛ Vin2 2 ⋅ Vin ⎞⎟ Vin2 ⋅ ⎜1 − →L ≤ 2 ⋅ Pin ⋅ fPFC,min Vout ⎟⎠ 2 ⋅ Pin ⋅ L ⎜⎝ ⎛ 2 ⋅ Vin ⎞⎟ ⋅ ⎜1 − = 2.6 mH ⎜ Vout ⎟⎠ ⎝ Lpfc = 1.5 mH is selected. The following graph depicts the frequencies that are obtained along the mains period for various input voltages. Doc ID 15599 Rev 1 5/31 Designing the application Figure 3. AN2982 PFC MOSFET frequencies along mains half period (fmains = 50 Hz) for various input voltages !-V The maximum choke current is equal to: Equation 5 IL,max = 2 ⋅ 2 ⋅ Pin = 1.93 A Vin,min A saturation current higher than IL,sat = 2.2 A is used in order to take into account the tolerance of this parameter. The RMS current flowing into the choke is equal to: Equation 6 IL,RMS = Pin = 787 mA 3 Vin,min 2 The choke form factor is an EF25 core (Ae = 52 mm2, le = 58 mm, material N87 or equivalent having Bmax<320 mT). Its design parameters are as follows: Equation 7 ⎫ ⎪ μ0N2A e ⎪ = 2.63 mm ⎬ → lgap = 2 × L L 2⎪ AL = 2 = 49.5 nH / turns ⎪⎭ N N= ImaxL = 174 turns BmaxA e The maximum power dissipation of the core should be less than 2.5 W in the worst condition. A multi-conductor wire is used in order to reduce the equivalent resistance at high frequency. 6/31 Doc ID 15599 Rev 1 AN2982 Designing the application When the maximum RMS current is obtained, the minimum frequency is detected and the RHF of the choke must be less than: Equation 8 RHF,max = PL,Ω 2 IL,RMS =4Ω Using a 13 x 0.1 mm2 wire, 3.5 Ω is obtained. The core losses, at minimum input voltage, are estimated below 0.35 W, therefore the total losses are lower than 2.5 W as expected. The higher the input voltage is, the lower the power dissipation (e.g. at 220 Vac the estimated total power losses are lower than 1.8 W). The transformer ratio can be calculated as: Equation 9 ( ) Vaux ,zcd = Vout − 2 ⋅ Vin > m ⋅ 1.4 V → m < 14.18 → m = 6 → N sec = 29turns Considering a maximum ZCD current equal to 1 mA, the limiting resistor is: Equation 10 R zcd = 1.2.3 2 ⋅ Vin,max m ⋅ IZCD → R zcd > 65.3 kΩ → R zcd = 75 kΩ MOSFET selection The PFC MOSFET must have a Vbdss = 500 V and a peak drain current greater than Id,max = 2.2 A. The maximum allowed MOSFET dissipation is equal to PMOS,max = 1 W in all conditions. The total power dissipation is composed of: ● Conduction losses, dominant at low input voltage: Equation 11 ⎛ P 2 PCOND = R ds,on ⋅ IMOS,RMS = R ds,on ⋅ 8⎜ in ⎜V ⎝ in,rms 2 ⎞ ⎡ 1 4 2 Vin,rms ⎤ 2 ⎟ ⎢ − ⎥ = R ds,on ⋅ 0.5278 A ⎟ 6 π 9 V ⎥ out ⎦ ⎠ ⎢⎣ Equation 12 RDS( on) (max) < ● PCOND,max 0.5278 A 2 Switching losses, directly proportional to the average switching frequency: Equation 13 fSW = Vin2,RMS ⎛ 2 2 VIN,RMS ⎞ ⎜1 − ⎟ ⋅ π 2 ⋅ Pin ⋅ L ⎜⎝ Vout ⎟⎠ Doc ID 15599 Rev 1 7/31 Designing the application AN2982 Equation 14 Pcross = t f fsw VOUT ● t f fsw Pin = ⋅ 25200 Vin,rms Vin,rms Capacitive losses, present only when Vin > Vout/2 and have their maximum at Vin,max The maximum time when the input voltage is greater than Vout/2 can be calculated as follows: Equation 15 ⎛ Vout arcsin⎜ ⎜ 2⋅ 2 ⋅V in,rms ⎝ t1 = 2πfmains t2 = ⎞ ⎟ ⎟ ⎠ → 1.8 ms 1 − t1 → 8.2 ms 2fmains Within this interval the capacitive losses are: Equation 16 ⎛ Pcap = fsw ⎜⎜ 3.3C oss VDrain ⎝ 3 2 + 1 (Crss + Coss + Cext ) VDrain 2 2⎞ ⎟ ⎟ ⎠ where <fsw> = 173 kHz and: Equation 17 VDrain = 2fmains ∫ [2 t2 t1 ] 2 ⋅ Vin,rms sin(ωt ) − Vout dt = 209.7 V 2 Using Equation 11 to 17 with the constraint Ptot < 1 W, the following parameters are found: – RDS(on) < 1.4 Ω (Pcond at 88 V < 0.75 W) – tf < 10 ns (Pcross at 88 V < 0.10 W) – Coss < 110 pF (considering Cext and Crss equal respectively 68 pF and 4 pF) The following ST MOSFETs meet these constraints: – STD5NK50Z – STD6NK50Z – STD7NM50N The STD7NM50N has RDS(on) = 1.12 Ω (at 100° C), tf = 9 ns and Coss = 67 pF and therefore is considered suitable for this design. The total power dissipation is shown in Figure 4. 8/31 Doc ID 15599 Rev 1 AN2982 Designing the application Figure 4. Summary of PFC MOSFET power losses !-V 1.2.4 Boost diode selection Both the boost diode maximum RMS current and the RMS current are equal to: Equation 18 Id,rms = 4 2 2 3 π Pin VOUT Vin,rms = 222 mA Their average current is equal to: Equation 19 P out ----------- = 142mA V out The STTH1L06 Shottky diode is selected, having Vrrm = 600 V and an average forward current If(AV) = 1 A. Total power dissipation is equal to: Equation 20 PD = 0.89 ⋅ 0.142 + 0.165 ⋅ 0.222 2 = 134.5 mW 1.2.5 Bulk capacitor selection The ripple superimposed on the output voltage is equal to ±20 V: Equation 21 ΔVout = 20 V = = Pout + [email protected],min ⋅ ICout ,RMS = 4π ⋅ fmains ⋅ Vout ⋅ C out 2.0463 × 10 − 4 + ESR ⋅ 373 mA C out Doc ID 15599 Rev 1 9/31 Designing the application AN2982 The RMS value of the bulk capacitor current is: Equation 22 ICout ,RMS = ⎛P Pin2 32 ⋅ 2 ⋅ − ⎜⎜ out 9π Vin,rms ⋅ Vout ⎝ Vout 2 ⎞ ⎟ = 373 mA ⎟ ⎠ Considering the first term of Equation 21 as dominant, Cout > 10.2 µF, and then Cout = 22 µF is selected. The voltage rating of the capacitor is equal to VCout = 450 V and the temperature class is TCout = 105 °C. With this value the typical ESR is around 2 Ω, adding only 740 mV to the total ripple. 1.2.6 Multiplier biasing and selection of PFC current sense resistor The peak values of the input voltage are between 124.4 V and 391.7 V. The ratio between these two values is equal to 3.15. The MULT pin is biased to 1 V when input voltage is equal to 124.4 V. If Rmulth = 3x680 kΩ: Equation 23 VMULT,1 kp = Vin,min Figure 5. = 0.00804 → Rmultl = pk kp Rmulth = 16.53 kΩ → R multh = 16.2 kΩ 1 − kp Multiplier bias points !-V with VCS,1 = 0.75 V: Equation 24 Rpfccs = VCS,1 IL,max = VCS,1 ⋅ Vin,min 2 ⋅ 2 ⋅ Pin = 0.364 Ω → R pfccs = 0.33 Ω A Cmult=1 nF capacitor is used in parallel with Rmultl for HF noise filtering. 10/31 Doc ID 15599 Rev 1 AN2982 1.2.7 Designing the application Error amplifier compensation Figure 6. Control loop block diagram !-V Equation 25 2 G(s) = 1 k Mk p Vin,rms R out 4 Vout Rpfcs 1 1 2 = 0.020308 ⋅ Vin,rms ⋅ R out C out 1 + 0.029623 s 1+ s 2 where: – kM = multiplier factor = 0.52 – kp = mult pin divider = 0.007879 – Rout = equivalent output resistor = 2.693 kΩ – Cout = 22 µF Using the simplest compensation network (a capacitor placed between the INV and COMP pin) whose transfer function is equal to: Equation 26 Gcomp (s ) = 1 1 = sC compRinvh sC comp ⋅ 6.6 MΩ and setting an open loop gain less than 0.001 when frequency is equal to twice the mains frequency, it is possible to calculate the minimum capacitance needed. Equation 27 ⎞ ⎛ 1 1 ⎟ ⋅ 0.020308 ⋅ Vin,rms 2 ⋅ Gloop (s ) = G(s ) ⋅ Gcomp (s ) = ⎜ ⎜ sC comp 6.6 MΩ ⎟ 1 + 0 . 029623 s ⎠ ⎝ = 0.001 s = 2 π100 Hz A Ccomp = 1 µF ceramic capacitor could be a good trade-off between performance and cost, but better performance can be obtained using a more complicated structure in order to obtain a phase margin equal to 45°. Doc ID 15599 Rev 1 11/31 Designing the application Figure 7. AN2982 Bode plot with simple compensation network: |Gloop|MAX < 35dB !-V For example, an RC-series network is connected between the INV and COMP pin. The obtained Gloop(s) can be written as: Equation 28 ⎛ 1 + sC compR comp Gloop (s ) = G(s ) ⋅ Gcomp (s ) = ⎜ ⎜ sC comp 6.6 MΩ ⎝ ⎞ 1 ⎟ ⋅ 0.020308 ⋅ Vin,rms 2 ⋅ ⎟ 1 + 0.029623 s ⎠ A phase margin equal to 45° is obtained at Vin = 277 Vac using Ccomp=1.5 µF and Rcomp=39 kΩ. At minimum input voltage the phase margin is equal to 85°. Higher values of Ccomp or a lower value of Cout can also improve the PFC performance. Figure 8. Bode plot with enhanced compensation network: |Gloop|MAX < 35 dB and Φ margin > 45° !-V 12/31 Doc ID 15599 Rev 1 AN2982 1.2.8 Designing the application Input rectifier A 2KBP06M bridge rectifier is able to sustain 600 V in reverse condition and 2 A of forward current. Its maximum power dissipation is equal to: Equation 29 PB = 2 2 1.2.9 Pin Vin,rms(min) VF = 1.73 W Input capacitor Let r = 10% be the maximum allowed ratio between the high-frequency ripple amplitude seen at the input of the PFC stage and the mean value of the input current: Equation 30 Cin,min = 1.2.10 Pin 2π ⋅ r ⋅ fsw ⋅ Vin,RMS(min) min 2 = 401.87 nF → Cin = 470 nF Input circuitry The input circuitry is composed of: – A fuse: avoids damage due to ballast breaking or excessive current from the mains – An NTC: limits the inrush current which avoids blowing the fuse and reduces the effects of a burst from the mains. This component reduces its resistance at a higher temperature. A 5 Ω NTC (at 25 °C) is used – A varistor (not present): absorbs the energy associated with a mains surge avoiding that Vout increases over the rated voltage of the components (Cout, MOSFETs, IC,…) – An EMI filter: an LC network able to reduce the HF noise coming from the application and traveling through the mains. This filter has to filter both the common mode component of the noise (which can be measured between the AC input and the EARTH) and the differential mode component of the noise (which can be measured between the two AC inputs) The first component (the fuse) is filtered by a CM filter (a current transformer that forces the AC input currents to travel in the opposite way) and two 1 nF capacitor placed between each AC input and EARTH. The second component (the NTC) is filtered by two capacitors placed across the AC inputs and by the leakage inductance of the CM filter. In fact by using a CM transformer having a high leakage inductance, a differential filtering can be obtained. The differential capacitors are equal to CX = 100 nF, while the CM capacitors are equal to CY = 1 nF. The CM transformer, TCM, is a B82733F series transformer from EPCOS. Doc ID 15599 Rev 1 13/31 Designing the application Figure 9. AN2982 Complete EMI filter (differential mode inductors are not present in this design) !-V 14/31 Doc ID 15599 Rev 1 AN2982 2 Ballast stage design Ballast stage design Figure 10. Resonant inverter simplified schematic !-V 2.1 Resonant network and operating point design Equivalent voltage applied to the resonant network: Equation 31 Vbal,pk = 2 Vout = 267.38 Vpk π L and C are chosen in order to fit the following constraints: ● Preheating voltage has to be less than 240 Vac = 339.4 Vpk ● Maximum striking voltage is equal to 700 Vac ● Nominal lamp voltage = 117 Vac ● Nominal lamp current = 0.46 A Selecting a common value equal to Lres=1.35 mH and Cres=4.7 nF, the following parameters are obtained: Equation 32 1 ⎧ = 64387 Hz ⎪f0 = 2 L C π res res ⎪ ⎪ L res ⎪ = 526 Ω ⎨Z 0 = Cres ⎪ ⎪ R ⎪Q = lamp = Vrun = 0.4836 ⎪⎩ Z0 Irun Z 0 Doc ID 15599 Rev 1 15/31 Ballast stage design AN2982 The run and preheating frequencies are calculated using the values calculated in Equation 33: Equation 33 frun = f0 2 ⎛ 4Vout 1 ⎞ 1 ⎞ ⎛ ⎛ ⎜2 − 2 ⎟ + ⎜2 − 2 ⎟ − 4 + ⎜ ⎜ Q ⎠ Q ⎠ ⎝ ⎝ ⎝ π ⋅ Z 0 ⋅ Q ⋅ 2Irun fpre = f0 1 + fign = f0 1 + 2 ⎞ ⎟ ⎟ ⎠ 2 = 48.5 kHz 2Vout > 86 kHz → fpre = 100 kHz πVpre 2Vout π ⋅ 2 ⋅ Vign ≈ 72.5 kHz Figure 11. Resonance curves !-V The maximum striking current is equal to: Equation 34 Iballast,ign ⎛ ⎜ ⎜ ⎜ 2⋅V out =⎜ ⎜ π ⋅ Z0 ⎜ ⎜⎜ ⎝ ⎛ fign 1 + ⎜⎜ Q ⎝ f0 ⎡ ⎛f ign Q 1 − ⎜⎜ ⎢ ⎝ f0 ⎣ 2⎢ ⎞ ⎟ ⎟ ⎠ 2⎤ 2 ⎞ ⎟ ⎟ ⎠ ⎛f ⎞ ⎥ + ⎜ ign ⎟ ⎜ f ⎟ ⎥ ⎝ 0 ⎠ ⎦ 2 ⎞ ⎟ ⎟ ⎟ ⎟ = 2.121 Apk ⎟ ⎟ ⎟⎟ ⎠ This current is also the saturation current of the ballast choke (Isat,ballast > 2.2 A). Limiting the current to this value, the lamp voltage is limited to 700 Vac (VCres,max > 700 Vac). The half-bridge current sense resistor is chosen according to: Equation 35 Rhbcs = 16/31 Vhbcsh Iballast,ign = 1 .6 V = 0.7543 Ω → R pfccs = 0.33 Ω 2.121 A Doc ID 15599 Rev 1 AN2982 Ballast stage design The RMS value of one side of the half bridge is equal to: Equation 36 Ihb,RMS ≈ Iballast,pk 2 = 1 2 ⋅ Vout ⋅ 2 π ⋅ Z0 ⎛ f ⎞ 1 + ⎜⎜ Q run ⎟⎟ ⎝ f0 ⎠ 2 2 ⎡ ⎛ f ⎞2 ⎤ ⎛ frun ⎞ 2⎢ run ⎟ ⎥ + ⎜⎜ ⎟⎟ Q 1 − ⎜⎜ ⎢ ⎝ f0 ⎟⎠ ⎥ ⎝ f0 ⎠ ⎣ ⎦ = 0.3465 A The power dissipation of the half-bridge current sense resistor is equal to: Equation 37 Phbcs ≈ Rhbcs ⋅ I2hbcs ,RMS < 100 mW A blocking capacitor Cblock = 100 nF (400 Vac) is used. The choke form factor is an EF25 core (Ae = 52 mm2, le = 58 mm, material N87 or equivalent having Bmax<300 mT). Its design parameters are as follows: Equation 38 ⎫ ⎪ μ 0N 2 A e ⎪ = 3.37 mm ⎬ → l gap = 2 × L L A L = 2 = 38.8 nH / turns 2 ⎪ ⎪⎭ N N= Imax L = 183 turns Bmax A e For this component a multi-conductor wire is also used to reduce the HF equivalent resistance, and therefore the power dissipation. 2.2 Selection of parameters Figure 12. Parameters setting block !-V Cosc = 1 nF (5% or better) is chosen. The following constant values are calculated (COSC in pF): Doc ID 15599 Rev 1 17/31 Ballast stage design AN2982 Equation 39 k= 499.6 ⋅ 10 3 (COSC )0.872 = 1209.55 Equation 40 e = 1− 1.33 (COSC )0.581 = 0.976 Given the run frequency and the preheating frequency (both in kHz), the following components are found: Equation 41 1 Rrun ⎛ k ⎞e ⎟ = 26.99 kΩ → Rrun = 26.7 kΩ = ⎜⎜ ⎟ ⎝ frun ⎠ Rpre // Rrun ⎛ k =⎜ ⎜ fpre ⎝ 1 ⎞e ⎟ = 12.86 kΩ → Rpre = Rrun ⋅ 12.86 kΩ = 24.9 kΩ ⎟ Rrun − 12.86 kΩ ⎠ An ignition time equal to 50 ms is obtained using a Cign corresponding to: Equation 42 Tign = 3Rpre Cign → C ign = 680nF A protection time equal to 120 ms is adopted, then: Equation 43 Tprot = 269740 ⋅ C d → Cd = 470nF The preheating time is equal to almost 1 s, therefore: Equation 44 Tpre = 4.63 Cd ITCH ⎛ 4.63 ⎞ + R d C d ln⎜ ⎟ → R d = 1.755MΩ ⎝ 1 .5 ⎠ The closest commercial resistor for Rd is 1.5 MΩ. With this value Tpre is equal to 865 ms. 2.3 Half-bridge design The maximum power loss acceptable for half-bridge MOSFETs is equal to 500 mW. Each MOSFET experiences a conduction loss equal to: Equation 45 P cond = RDS( on ) ⋅ (Irms ) <0.25 W 2 With Irms2 = 0.120 A2, a maximum RDS(on)= 2.08 Ω is obtained. 18/31 Doc ID 15599 Rev 1 AN2982 Ballast stage design The following ST MOSFETs meet these constraints: – STD5NK50Z – STD6NK50Z – STD7NM50N The STD7NM50N has RDS(on)= 1.12 Ω (at 100°C), therefore the power dissipation related to the half-bridge MOSFETs is equal to almost 270 mW. The size of the boostrap capacitor can be calculated by solving the following equation: Equation 46 C gate + Cboot,min = Cboot,min ⋅ Vcc Vcc − ΔV where: ΔV = Vcc,min - Vgate,min = 9.6 V - 8 V = 1.6 V Vcc = 15 V - Vf, Vf = forward voltage of charge pump diode = 0.8 V Qg = total gate charge of STD7NM50N = 12 nC Cgate = Qg/Vcc = 845 pF Cboot,min = 6.6 nF is obtained A Cboot = 100 nF is selected and the voltage drop is equal to ΔV = 120 mV. The charging time of the capacitor is calculated to check if ΔV is compensated during the on-time of the low side. The time the capacitor takes to charge to 95% of Vcc starting from 0 is equal to: Equation 47 t 0 = 3 ⋅ Rboot ⋅ Cboot = 3 ⋅ 250 Ω ⋅ 100 nF = 75 μs The time the capacitor takes to charge to 95% of Vcc minus 120 mV starting from 0 is equal to: Equation 48 ⎛ 0.95 ⋅ Vcc − 0.12 ⎞ ⎟ = 2.839 ⋅ Rboot ⋅ Cboot = 71 μs t1 = −Rboot ⋅ Cboot ⋅ ln⎜⎜1 − ⎟ Vcc ⎠ ⎝ The difference t0 - t1 = 4 µs is smaller than the minimum on-time equal to: Equation 49 Ton,min = 1 − TDEAD,max = 4.11 μs 2fpre The selected capacitor is able to correctly supply the high-side driver. Doc ID 15599 Rev 1 19/31 Ballast stage design 2.4 AN2982 End of life detection In this design the blocking capacitor to ground configuration is chosen. Figure 13. Blocking capacitor to ground topology !-V The tracking configuration with a window of amplitude equal to 240 mV is selected, connecting EOLP to ground with REOLP = 240 kΩ. The EOL pin detects the blocking capacitor voltage by means of a voltage divider that, in normal conditions, sets its voltage to the same value as the CTR pin: Equation 50 VCTR,0 = Vout R ctrl = 3.03 V ← VEOL R ctrl + R ctrh Choosing the total upper resistor value equal to Reol1 = 1.36 MΩ (2x680 kΩ), and with the steady-state value of the blocking capacitor voltage equal to Vout/2, the lower resistor is calculated as: Equation 51 Reol2 = R eol1 2VEOL = 19.9 kΩ → Reol2 = 20 kΩ VOUT − 2VEOL A Ceol = 10 nF capacitor is used to filter the lamp frequency, maintaining the ripple. The obtained cutoff frequency is calculated higher than 100 Hz, but lower than 49 kHz. Equation 52 fc,eol ≈ 20/31 1 = 796 Hz 2π ⋅ Reol2 ⋅ C eol Doc ID 15599 Rev 1 AN2982 2.5 Ballast stage design IC power supply design The IC current consumption depends on both the PFC frequency and half-bridge frequency. In the worst case, the mean value of the PFC frequency is equal to 162 kHz and the maximum half-bridge frequency is equal to 90 kHz. With these values the maximum supply current is approximately equal to: Equation 53 IccmA = 0.0192 ⋅ fPFC kHz + 0.0373 fprekHz + 4.56 ≈ 11 mA This current is delivered to the IC by means of a charge pump connected to the middle point of the half bridge. Figure 14. Charge pump network and startup !-V The current delivered by the charge pump capacitor is approximately: Equation 54 Icp = Icp,pk ⋅ Trise ⋅ frun ≥ Icc where: Equation 55 Icp,pk = C cp Vout Trise and rearranging the terms: Equation 56 C cp ≥ Icp VOUT ⋅ frun = 558 pF → C cp = 1 nF The startup network works also as a detector of lamp presence. This feature can be implemented by placing one or both of the lamp cathodes along the startup network path. If the lamp is absent, the IC cannot start. Doc ID 15599 Rev 1 21/31 Ballast stage design AN2982 The minimum startup current of the L6585DE is equal to Icc,on = 370 µA. This current has to be delivered to the IC at the minimum input voltage (125 Vpk), therefore a total resistance equal to: Equation 57 R su,tot = Vin,min Icc,on = 337 kΩ The network is divided into 5 x 68 kΩ resistors in order to avoid damage due to the lamp striking voltage. A C1 = 10 µF followed by a 100 nF ceramic capacitor is used as the Vcc bulk capacitor. 22/31 Doc ID 15599 Rev 1 AN2982 3 Demonstration board schematic and bill of material Demonstration board schematic and bill of material Figure 15. STEVAL-ILB005V2 schematic !-V Doc ID 15599 Rev 1 23/31 Demonstration board schematic and bill of material Table 2. AN2982 BOM Reference Value Note R1 681 kΩ R2 681 kΩ R3 681 kΩ R4 16.2 kΩ R5 2.2 MΩ R6 2.2 MΩ R7 2.2 MΩ R8 39.2 kΩ R9 n.m. R10 75 kΩ Rzcd R11 47 Ω PFC MOSFET gate resistor R12 220 Ω PFC current sense filtering resistor R13 825 kΩ R14 825 kΩ R15 825 kΩ R16 18 kΩ Rctr,lo R18 26.1 kΩ Rrun R19 29.4 kΩ Rpre R20 1.5 MΩ RD R21 0R0 R22 240 kΩ R23 0R0 R24 47 Ω High-side MOSFET gate resistor R25 47 Ω Low-side MOSFET gate resistor R26 3.3 Ω R27 3.3 Ω R28 68 kΩ R29 68 kΩ R30 560 kΩ R31 120 kΩ R32 20.5 kΩ R33 68 kΩ R34 68 kΩ R35 68 kΩ Rmult,hi Rmult,lo Rinv,hi Rinv,lo Rctr,hi Reolp Charge pump limiting resistor Startup network 24/31 Doc ID 15599 Rev 1 REOL,hi (1) REOL,lo Startup network AN2982 Demonstration board schematic and bill of material Table 2. BOM (continued) Reference Value Note R40 680 kΩ REOL,hi (2) R41 n.m. RS1 0.33 Ω – 0.5 W Rpfccs RS2 0.82 Ω – 0.5 W Rhbcs C1 22 µF – 450 V COUT CA1 0R0 C2 470 nF – 305 Vac Cin C3 4.7 nF MULT filtering capacitor C4 1 nF PFCCS filtering capacitor C5 1 µF Ccomp C6 n.m. C7 10 nF CTR filtering capacitor C8 1 nF - 1% Cosc C9 1 µF Cign C10 470 nF Cd C11 100 nF Cboot C12 1 nF - 630Vdc Ccp C13 10 µF CVcc C14 100 nF CVcc,b C15 4.7 nF - 2 kV Cres C16 100 nF - 630Vdc Cblock C17 10 nF EOL filtering capacitor C18 1 nF C20 100 nF, X2, 275Vac Differential mode EMI filter C21 100 nF, X2, 275Vac Differential mode EMI filter C22 1 nF Y1 Common mode EMI filter (capacitive) C23 1 nF Y1 Common mode EMI filter (capacitive) C24 0R0 D1 STTH1L06 Boost diode D2 1N4148 Charge pump forward diode D3 1N4148 PFC gate speed-up diode DZ1 BZX84C15 Charge pump free-wheeling Zener diode DZ2 0R0 DZ3 0R0 DZ4 n.m. Doc ID 15599 Rev 1 25/31 Demonstration board schematic and bill of material Table 2. 3.1 AN2982 BOM (continued) Reference Value Note B1 2KBP06M Rectifier bridge U1 L6585DE Ballast controller Q1 STD7NM50N PFC MOSFET Q2 STD7NM50N Half-bridge high-side MOSFET Q3 STD7NM50N Half-bridge low-side MOSFET T1 1.5 mH - 2.6 A PFC transformer – EPCOS B78313P8140 T2 2 x 68 mH - 0.9 A Common mode EMI filter – EPCOS B82733F2901 L1 1.3 mH - 2.6 A Ballast choke – ITACOIL E2543-H F1 T 2 A – 250 Vac Fuse RT1 NTC 5 Ω Inrush current limiter Demonstration board performances Figure 16. Input performance - power factor Figure 17. Input performance - total harmonic distortion 34%6!,),"64($ 34%6!,),"60& 0& 4($ 6IN6AC Figure 18. EMI spectrum at 277 Vac !-V Figure 19. EMI spectrum at 88 Vac !-V 26/31 6IN6AC !-V Doc ID 15599 Rev 1 !-V AN2982 3.2 Demonstration board schematic and bill of material Ballast stage performance and reliability Figure 20 shows the lamp parameters. Small discrepancies between theoretical and real measurements are due to the tolerance of the passive components of the resonance network (Lres and Cres). Figure 20. Steady-state lamp parameters !-V Figure 21 summarizes the Tch sequences during preheating and protections. During the open lamp test, Tch voltage (lower trace) sets the preheating time (Tpre = 805 ms). After that the lamp voltage (upper trace) increases up to the maximum value allowed by the HBCS resistor (740 Vrms). The subsequent protection time is shorter than the preheating time (120 ms). Figure 21. Startup sequence with open lamp protection !-V In Figure 22 a close-up of the waveforms during a ballast choke saturation is shown. The upper graph illustrates the lamp parameters. While the lamp voltage remains essentially sinusoidal, the lamp current becomes triangular cycle by cycle. The lower trace illustrates the half-bridge current sense voltage (VHBCS). As soon as this voltage reaches 2.75 V, the application is immediately stopped. The saturation effect does not have a definite threshold. Once the current is close to saturation, the inductance value starts to decrease slowly and constantly, therefore a current Doc ID 15599 Rev 1 27/31 Demonstration board schematic and bill of material AN2982 limiting that maintains the frequency constant is not suitable to counter this effect. Actually the application should be stopped as soon as the saturation effect is detected. Figure 22. Ballast anti-choke saturation protection !-V Asymmetrical ageing of the lamp is detected by the EOL pin. Figure 23 and 24 illustrate the behavior of this protection. In the upper trace the lamp voltage and Tch voltage are shown. When the lamp starts ageing, the lamp voltage increases in one direction. The EOL voltage (lower trace) moves together with the blocking capacitor voltage. Once the difference between the CTR voltage and the EOL voltage is higher than 240 mV, a Tch cycle is started and the application is stopped if this situation persists. Figure 23. EOL protection (positive deviation) !-V 28/31 Doc ID 15599 Rev 1 AN2982 Demonstration board schematic and bill of material Figure 24. EOL protection (negative deviation) !-V Doc ID 15599 Rev 1 29/31 Revision history 4 AN2982 Revision history Table 3. 30/31 Document revision history Date Revision 15-Mar-2010 1 Changes Initial release. Doc ID 15599 Rev 1 AN2982 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 herein 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 assumes 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. If 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 whatsoever of such third party products or services or any intellectual property contained therein. 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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 whatsoever, 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. © 2010 STMicroelectronics - All rights reserved STMicroelectronics group of companies Australia - Belgium - Brazil - Canada - China - Czech Republic - Finland - France - Germany - Hong Kong - India - Israel - Italy - Japan Malaysia - Malta - Morocco - Philippines - Singapore - Spain - Sweden - Switzerland - United Kingdom - United States of America www.st.com Doc ID 15599 Rev 1 31/31

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