AN2640 Application note Intelligent multipower digital ballast for fluorescent lamps Introduction Fluorescent lamps are highly popular due to their luminous efficiency, long life and color rendering. These lamps need external circuitry to compensate for their negative resistance characteristic. This circuitry is called "ballast". The simplest ballast is a magnetic inductor connected in series at the lamp. The electronic ballast with respect to the magnetic one offers the following advantages: ■ Better efficiency ■ Increased lamp life ■ Lightweight with smaller dimensions ■ Better lamp power control For these reasons, in the last years there has been a shift in the market towards the use of electronic ballasts with dedicated drivers and controllers. Today, thanks to microcontrollers, it is possible to add intelligence into the circuit. Instead of having a dedicated circuit for each lamp with a single ballast it is possible to drive many different lamp groups. This application note describes an electronic ballast that is able to recognize lamps within the T5 fluorescent family such as 24 W, 39 W, 54 W and 80 W. It consists of two main blocks: ■ A boost converter (Power Factor Controller PFC) working in transition mode (fixed TON and variable frequency) ■ An inverter in half-bridge configuration working in zero voltage switching Both ballast and PFC stages are controlled by the ST7FLIT19B that offers its entire signal to the L6382D5 which provides the right voltage and current levels for the Power MOSFET. This system after tube recognition sets the right parameter and drives the lamp correctly. Figure 1 shows the ballast block diagram. Figure 1. January 2008 Ballast block diagram Rev 1 1/36 www.st.com Contents AN2640 Contents 1 PFC section design criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.2 Boost inductor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.3 PFC devices selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.3.1 Power switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 1.3.2 Rectifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2 Half-bridge design criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 3 ST7LIT19BF1 - 8-bit MCU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 4 5 3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 3.2 Use of the pins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 L6382D5 - power management units for microcontrolled ballast . . . . 18 4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 4.2 Use of the pins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Recognition technique . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 5.1 6 Code implementation on microcontroller . . . . . . . . . . . . . . . . . . . . . . . . . 23 Board description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 6.1 Electrical schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 6.2 Bill of materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 6.3 Experimental results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 6.3.1 From system switch on to ballast run . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 6.3.2 PF, THD and ballast efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 6.3.3 Electromagnetic compatibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 7 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 8 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 9 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 2/36 AN2640 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. Figure 25. Figure 26. Figure 27. Figure 28. Figure 29. Figure 30. Figure 31. Figure 32. Figure 33. Figure 34. Figure 35. Ballast block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 The step-up "Boost" regulator. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Inductor current waveform and MOSFET timing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 24 W lamp power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 39 W lamp power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 54 W lamp power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 80 W lamp power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 ST7LITE1xB general block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 ST7LITE1xB 20-pin SO and DIP package pinout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 PFC overcurrent detection circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 PFC Vout sense circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 PFC Vin waveform circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Average current circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Lamp type detection circuit (a) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Lamp type detection circuit (b) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Peak lamp voltage circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Average lamp voltage circuit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Lamp detection circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Zero-current detection circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 L6385Dx block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Typical L6385Dx use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Circuit connected at CSI pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Ballast operation sequence flowchart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 STEVAL-ILB004V1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Electrical schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 L6382 startup sequence and ballast start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 24 W lamp power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 39 W lamp power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 54 W lamp power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 80 W lamp power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Test equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 24 W . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 39 W . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 54 W . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 80 W . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 3/36 PFC section design criteria AN2640 1 PFC section design criteria 1.1 Introduction The following data are needed to calculate the input and output capacitors and the boost inductance: ● Mains range (Virms(min) and Virms(max)) ● Regulated DC output voltage (Vo) ● Rated output power (Po) ● Minimum switching frequency (fswmin) ● Maximum output voltage ripple (∆Vo) ● Expected efficiency (η) ● Maximum mains RMS current (Irms) ● Rated output current Io Input capacitor The input capacitor that has been chosen is 470 nF. Using this value good performances in terms of power factor and current distortion have been obtained with the lamps that can be driven. Output capacitor The output bulk capacitor (Co) selection depends on the DC output voltage and the ripple on it. For lighting applications the ripple, 2*∆Vo, is typically 5% of the output voltage. The output bulk capacitor has been calculated using the following formula: Equation 1 Io Po C o ≥ ---------------------------------------- = -----------------------------------------------------4 ⋅ π ⋅ f ⋅ ∆V o 4 ⋅ π ⋅ f ⋅ V o ⋅ ∆V o Where: ● f= 50 Hz (mains frequency) ● Vo= is the output voltage (420V) ● ∆Vo= (½ ripple peak-to-peak value at 5%) is 10.5 V ● Io= is the output peak current capacitor ● Po(max)= (lamp specifications) therefore 4/36 ● Co ≥ 30.7 µF ● Co was selected as 47 µF AN2640 1.2 PFC section design criteria Boost inductor To define the PFC inductor several parameters are involved. The formula used to obtain the inductance value is: Equation 2 2 V irms ( min ) ⋅ ( V o – 2 ⋅ V irms ( min ) ) L = ---------------------------------------------------------------------------------------------2 ⋅ f sw ( min ) ⋅ P i ⋅ V o Where ● fsw(min)= 35 kHz ● Virms(min)= 185 V ● Pi= Po/η ● Po is the lamp power ● η is the estimated efficiency (0.9) For multipower ballast the inductance calculation must be performed adopting the maximum lamp power (85 W). Using these parameters L = 1.95 mH. An inductance value of 2 mH ± 5% is chosen. The switching frequency of PFC power transistor can be obtained using the following formula: Equation 3 2 V irms ⋅ ( V o – 2 ⋅ V irms ⋅ sin Θ) 1 f sw = -------------------------- ⋅ -----------------------------------------------------------------------------------------Vo 2 ⋅ L ⋅ Pi Notice that increasing the inductance value L decreases the PFC switching frequency. 1.3 PFC devices selection The PFC is a step-up "Boost" regulator, therefore in normal operation the energy is fed from the inductor to the load and then stored in the output capacitor Figure 2. The step-up "Boost" regulator 5/36 PFC section design criteria Figure 3. 1.3.1 AN2640 Inductor current waveform and MOSFET timing Power switch It must be: ● VDSS > Vout ● ID > IT(pk) Equation 4 V out = 420 V Equation 5 P omax = 85 W Equation 6 η = 0.9 Equation 7 P omax P imax = ---------------- ≅ 95 W η Equation 8 V imin ( rms ) = 185 V Equation 9 P imax I Lmax ( rms ) = -------------------------- ≅ 510 mA V imin ( rms ) Equation 10 I L ( pk ) = 2 ⋅ 6/36 2 ⋅ I Lmax ( rms ) ≅ 1.5 A AN2640 PFC section design criteria For safety reasons we must choose a device with: ● VRRM 20% more Vout, that is, 504 V ● IF(av) 3 times more Iout, that is, 4.5 A (to be considered transient current) The STP6NK60Z, a Zener-Protected SuperMESH™ MOSFET, satisfies these specifications. Table 1. 1.3.2 STP6NK60Z general features VDSS RDS(on) ID 600 V < 1.2 Ω 6A Rectifier It must be: Equation 11 V RRM > V out = 420 V Equation 12 P omax I F ( av ) > I out = ---------------- ≅ 200mA V out For safety reasons we must choose a device with: ● VRRM 20% more Vout, that is, 504 V ● IF(av) 3 times more Iout, that, is 600 mA The STTH1L06, a turbo 2 ultrafast, high-voltage rectifier, was selected because it is especially suitable as a boost diode in discontinuous or critical mode power factor corrections. Table 2. STTH1L06 general features IF(AV) VRRM VF(typ) trr(max) 1A 600 V 1.05 V 80 ns 7/36 Half-bridge design criteria 2 AN2640 Half-bridge design criteria The design of the half-bridge section involves dimensioning the resonant components: ballast inductor and startup capacitor. The component design is not an easy matter and several parameters must be considered, especially when different lamps must be driven with the same resonant components. The main parameters to be considered are preheating current and voltage, maximum preheating voltage, maximum ignition voltage and run lamp voltage. For each lamp the transfer function was plotted in order to evaluate the operating point in terms of preheating and run frequency. The resonant inductor has been chosen as 1.2 mH and the startup capacitor has been chosen as 10 nF. 8/36 Figure 4. 24 W lamp power Figure 5. 39 W lamp power AN2640 Half-bridge design criteria Figure 6. 54 W lamp power Figure 7. 80 W lamp power During the preheating phase in this system the half-bridge works at fixed frequency and the selected preheating frequency is the best choice according to the selected lamp specifications. This working frequency guarantees the right preheating current for all lamps that can be driven by this system. After tube recognition the microcontroller sets the right run frequency for the connected lamp. 9/36 ST7LIT19BF1 - 8-bit MCU 3 ST7LIT19BF1 - 8-bit MCU 3.1 Introduction AN2640 The ST7LIT19BF1 is a member of the ST7 microcontroller family. All ST7 devices are based on a common industry-standard 8-bit core, featuring an enhanced instruction set. Figure 8. ST7LITE1xB general block diagram The ST7LIT19BF1, moreover, is a microcontroller designed for lighting applications. 10/36 AN2640 ST7LIT19BF1 - 8-bit MCU The following are a few main features that make this microcontroller suitable for this scope: ● Internal RC oscillator with 1% precision at 8 MHz CPU frequency ● 32 MHz timer counter clock with two independent counters for half-bridge and PFC management ● Analog PFC zero-current detection and half-bridge dead time generation ● Analog comparator ● 10-bit A/D Converter with 7 channels and the possibility to use an amplifier (fixed gain 8) between the input and converter ● 2 timers with 1 ms or 2 ms time base to provide timing to the system management Figure 9. 3.2 ST7LITE1xB 20-pin SO and DIP package pinout Use of the pins ● Pin 1: GND ● Pin 2: VCC. The microcontroller is supplied by means of this pin. The voltage is generated by the L6382D5 device. To prevent noise in this pin a 100 nF capacitor must be soldered as close as possible between this pin and GND. ● Pin 3: reset (not used). It is advisable to connect a small capacitor to avoid undesired reset of the micro between this pin and GND. ● Pin 4: COMPIN+. This pin is used to protect against overcurrent on the PFC Power MOSFET and inductor. When the current exceeds 2 A, the comparator inside the MCU stops the ballast without using the MCU core. Figure 10 shows the detection circuit. 11/36 ST7LIT19BF1 - 8-bit MCU AN2640 Figure 10. PFC overcurrent detection circuit ● Pin 5: AIN1 - PFC Vout sense. This pin is used to perform the PFC Vout voltage protection and regulation. Figure 11 shows the circuit for the PFC Vout sense. Figure 11. PFC Vout sense circuit In this pin the MCU reads the voltage on the C6 capacitor and converts this value to a digital one which is proportional to the DC bus voltage. ● 12/36 Pin 6: AIN2 - PFC Vin waveform. The circuitry shown in Figure 12 measures the input voltage and the voltage across R5-C4 is used by the MCU to understand the instantaneous main voltage. AN2640 ST7LIT19BF1 - 8-bit MCU Figure 12. PFC Vin waveform circuit ● Pin 7: AIN3 - average current. In the ballast during the run state the inductor current is controlled by monitoring the voltage across Rsense. Figure 13. Average current circuit The voltage across C22 is proportional to the current that flows in the Power MOSFET which is related to the discharge current in the tube. When ballast frequency is changed, a current regulation is performed. ● Pin 8: AIN4 - lamp type detection. This circuit is used to distinguish between lamps having different cathode resistances. When the NPN transistor Q5 is in the cutoff region, the PNP transistor Q4 is also, producing a voltage close to zero at pin 8 "Lamp Type Detection". When the NPN transistor Q5 is in the saturation region, the PNP transistor Q4 is also, producing at pin 8 "Lamp Type Detection" a voltage that depends on the resistor of the lamp electrodes. Normally the NPN transistor Q5 is kept in the cutoff region so that the whole circuit is disabled. This circuit is enabled just to recognize the lamp family, after recognition, it is disabled. 13/36 ST7LIT19BF1 - 8-bit MCU AN2640 Figure 14. Lamp type detection circuit (a) Figure 15. Lamp type detection circuit (b) ● 14/36 Pin 9: AIN5 - peak lamp voltage. Using the circuit shown in Figure 16, it is possible to measure the voltage across the lamp. AN2640 ST7LIT19BF1 - 8-bit MCU Figure 16. Peak lamp voltage circuit The resistors R31 ÷ R34 form a voltage divider and the voltage across R36-C23 is used to control the voltage on the lamp during all lamp phases. ● Pin 10: AIN6 - average lamp voltage Figure 17. Average lamp voltage circuit The circuit shown in Figure 17 is used to detect asymmetrical lamp voltage when lamp rectification happens. ● Pin 11: PA7 - lamp detection 15/36 ST7LIT19BF1 - 8-bit MCU AN2640 Figure 18. Lamp detection circuit The circuit shown in Figure 18 connected at this digital input is used to detect the lamp presence. If the lamp is present, the cathode is in parallel to R30 and C17 and the voltage across C17 is low. The low voltage is used by the micro to sense the lamp presence. If the lamp is not present or the cathode is broken, the voltage across C17 is high (5 V) and the MCU stops the ballast. ● Pin 12: PA6 (not used). This pin is connected at micro VCC voltage by means of a 10 kΩ resistor because this pin is also used as ICCCLK and during normal operation it must be pulled up, internally or externally (external pull-up of 10 kΩ is mandatory in noisy environments). ● Pin 13: PWM3 - PFC gate driver. This pin is connected to the L6382 driver in order to control the PFC PMOS. ● Pin 14: PA4 (not used). This pin is connected to micro VCC voltage by means of a 10 kΩ resistor because an unused pin must be kept at a fixed voltage. It can be left unconnected if it is configured as output (0 or 1) by the software. ● Pin 15: PWM1 - High side input. This pin is connected to the L6382 driver and the signal is used to drive the High side PMOS. ● Pin 16: PWM0 - Low side input. This pin is connected to the L6382 driver and the signal is used to drive the High side PMOS ● Pin 17: PA1 - CSO. This pin is connected to the CSO pin of the L6382 and can be used to lock the ballast when the CSI pin is high. ● Pin 18: LTIC - Zero-current detect Figure 19. Zero-current detection circuit 16/36 AN2640 ST7LIT19BF1 - 8-bit MCU The zero-current detection circuit switches the external MOSFET ON as soon as the voltage across the boost inductor reverses or the current through the boost inductor goes to zero. This feature allows the transition mode operation. The signal for ZCD is obtained with an auxiliary winding on the boost inductor. The secondary winding is connected to the LTIC pin by means of a resistor. The MCU detecting negative dv/dt gives the turn-on signal to the driver for the Power MOSFET commutation. ● Pin 19: PC1 (not used). This pin is connected to micro VCC voltage by means of a 10 kΩ resistor because an unused pin must be kept at a fixed voltage. It can be left unconnected if it is configured as output (0 or 1) by the software. ● Pin 20: Lamp Type Detection Circuit Enable. This pin is used to enable the "Lamp Type Detection Circuit". 17/36 L6382D5 - power management units for microcontrolled ballast 4 L6382D5 - power management units for microcontrolled ballast 4.1 Introduction AN2640 This driver allows powering efficiently all the ICs (PFC, microcontroller, driver) in all conditions and allows the microcontroller to drive the MOSFET (both half-bridge and PFC) without using numerous different drivers. Figure 20. L6385Dx block diagram The L6382D5 ICs (Figure 20) include 3 MOSFET driving stages (for PFC, for the halfbridge, for the preheating MOSFET) plus a power management unit (PMU) able to supply the microcontroller in any condition by means of a voltage reference available at a pin. It has a precise reference voltage (5VDC ±2%, overall temperature range) able to provide up to 30 mA to supply the microcontroller. The L6382D5 also integrates a function that regulates the IC supply voltage without the need of any external charge pump and optimizes the current consumption (Figure 21). The L6382D5 reduces the application bill of materials because many different tasks (regarding drivers and power management) are performed by a single IC, which of course improves application reliability. 18/36 AN2640 L6382D5 - power management units for microcontrolled ballast Figure 21. Typical L6385Dx use Another feature of the driver is the internal interlocking that avoids cross-conduction in the half-bridge FET's. If by chance both HGI and LGI inputs are brought high at the same time, then LSG and HSG are forced low as long as this critical condition persists. A current sense is also available in this driver. When the voltage on pin CSI overcomes the internal comparator reference (0.56 V, typ), the block latches the fault condition. In this state the OCP block forces both HSD and LSD signals low while CSO is forced high so that it can be sent to an input pin of the microcontroller that, based on its programming, starts the proper protection sequence. The CSO output remains latched high until LSI and HSI are simultaneously low (e.g. during dead time) and CSI is below 0.5 V. This function is suitable to implement an overcurrent protection or hard-switching detection by using an external 19/36 L6382D5 - power management units for microcontrolled ballast AN2640 sense resistor. As the voltage on pin CSI can go negative, the current must be limited below 2 mA by external components. 4.2 Use of the pins A short description of each pin function is given below. 20/36 ● Pin 1: PFI. This pin receives a digital input signal from the ST7 micro to control the PFC gate driver. We advise connecting a capacitor for noise filtering between this pin and GND. In this application a 33pf capacitor is used. ● Pin 2: LSI. This pin receives digital input signal from the ST7 to control the low side switch in the ballast. ● Pin 3: HSI. This pin receives digital input signal from the ST7 to control the high side switch in the ballast. ● Pin 4: HEI (not used). This pin receives digital input signal from the ST7 to control the HEG driver. ● Pin 5: PFG. This pin is able to drive an external MOSFET with a sink current capability of 120 mA and a source current capability of 250 mA. A 10 Ω resistor is connected between this pin and the Power MOSFET gate to reduce the peak current. ● Pin 6: not connected ● Pin 7: TPR. This pin is connected by means of an RC net to the half-bridge midpoint in order to form a charge pump circuit charging the capacitor connected to the VCC pin. In this application a capacitor of 1 nF at 630 V and a resistor of 44 Ω (2 x 22 Ω) have been mounted. The high voltage capacitor in this connection also performs the snubber function in the half-bridge section limiting the slope during the voltage variation. ● Pin 8: GND. On the GND traces it is better to keep separate power traces from the signal and a star connection of these tracks is advisable. ● Pin 9: LSG. This pin is connected to the Power MOSFET gate of the low side of the half-bridge. This pin has 120 mA as source and sink current capability. A 33 Ω resistor is connected between this pin and the MOSFET gate to limit the peak current. At turnoff a net composed of a diode and a 33 Ω resistor reduces the resistance which decreases the turnoff time. ● Pin 10: VCC. This pin provides the supply voltage to the driver. A capacitor of 47 µF is connected between this pin and GND and in parallel another small capacitor is mounted. ● Pin 11: BOOT. This pin provides the supply voltage at the high side gate driver. A 100 nF capacitor is connected between this pin and the out pin of the driver. This AN2640 L6382D5 - power management units for microcontrolled ballast capacitor is supplied thanks to a patented structure that replaces an external diode connected between this capacitor and VCC. ● Pin 12: HSG. The same as pin 9 but is able to drive the half-bridge high side Power MOSFET gate. ● Pin 13: OUT. This pin is the high side floating ground and it is connected at the midpoint of the half-bridge. ● Pin 14: not connected ● Pin 15: HVSU. This pin allows driver startup and two resistors of 10 Ω are connected at the DC bus according to the Vref current requirement. ● Pin 16: not connected ● Pin 17: HEG (not used) ● Pin 18: CSO. This pin is the output of the current sense comparator. During normal operation this pin is forced low, but if the voltage on the CSI pin exceeds 0.55 V this pin is high with 5 V logic level. ● Pin 19: CSI. This is the input of the current sense comparator.The circuit that is connected at this pin is shown in Figure 22. During the operating mode if overcurrent occurs in the half-bridge, the voltage on the R28 resistor increases and when it exceeds 0.55 V, the L6382 forces both half-bridge drivers low. This condition remains until the input signals LGI and HGI are low simultaneously (dead time) or Vcc is below the undervoltage lockout. Figure 22. Circuit connected at CSI pin The capacitor C20 is used to filter the voltage on the CSI pin. ● Pin 20: Vref. This pin provides a precise voltage reference of 5 V with a current capability up to 30 mA. This voltage is used to supply the ST7 microcontroller which avoids adding external components. To ensure voltage stability and prevent noise, a 220 nF capacitor is recommended between this pin and GND. 21/36 Recognition technique 5 AN2640 Recognition technique To identify the connected lamp, the power must be evaluated by measuring both the lamp voltage and current. In this way, by multiplying these measurements, it is possible to obtain the lamp power: Equation 13 P lamp = V lamp ⋅ I lamp With the evaluation board based on STMicroelectronics' ST7FLIT19BF1 MCU and L6382D5 driver, the lamp power measurements can be easily calculated. Our proposal is based on a patented method that evaluates the PFC TON. The PFC is a boost converter working in transition mode (TM). In the transition mode operation the boost converter works with a fixed switch conduction time, TON, and variable frequency. To measure the lamp power the constant TON is evaluated and moreover the TON is proportional at the load power as shown in the following relationship: Equation 14 2⋅ L⋅ P T ON = ---------------------------o2 V inr Where: ● TON is the PFC switch conduction time ● L is the PFC inductor value ● Vinrms is the RMS AC input voltage ● Po is the load power, that is, the lamp power This technique provides a key advantage of obtaining the lamp power information by directly reading the PFC conduction time without multiplier evaluations in the board. When the mains is switched ON the microcontroller performs a measurement on the AC input voltage. After this phase it starts the half-bridge. The PFC is activated during this initial phase to distinguish the family type and a cathode resistance measurement is performed to select the lamp type. After this selection, the preheating phase is performed until the ignition phase turns the lamp on. After the ignition the connected lamp is recognized and starts the run phase. Using the described technique it is simple to calculate the lamp power. Experimental results have confirmed this data. 22/36 AN2640 5.1 Recognition technique Code implementation on microcontroller Figure 23. Ballast operation sequence flowchart Start Clear previous error information Oscillator Init Enable Interrupts Port Init VIN Recognize Analog Comparator Init ADC Init Lamp Detection Lite Timer Init Ballast Control Auto Reload Timer Init PFC Control PFC Init Is the lamp connected? No Yes 23/36 Board description 6 Board description Figure 24. STEVAL-ILB004V1 24/36 AN2640 1n 275VAC C2 J5 2 1 R28 820 AverageCurrent PFC VinWaveform PFC Vout Sense PFC OC 10nF C10 AverageLampVoltage PeakLampVoltage LampTypeDetection RESET VDC-5V-programm. CSI AverageCurrent AC L N PE J1 C9 220nF C20 1n C22 470n Out pin 1nF 630V C8 3 + + + + + J3 C3 + + + + + 2 4 6 8 10 R5 18k R4 750k R3 750k R46 0.6W 22 R16 0.6W 22 ST7LITE1B 20pin RESET C27 10p C26 10p 100p C4 20 19 18 17 16 15 14 13 12 11 R43 10k 10k 1 2 3 4 5 6 7 8 9 10 C12 100nF 10k R45 10p C25 C11 + 47uF 35V R44 D4 T2 VREF CSI CSO HEG NC HVSU NC OUT HSG BOOT LampPresence PFC Gate Driver High Side Input Low Side Input 10p 2 1N4007 D12 2.0mH 20 19 18 17 16 15 14 13 12 11 R22 33 10 R7 27k C28 R6 L6382 PFI LSI HSI HEI PFG NC TPR GND LSG VCC U2 PFC Mosfet Gate PFC VinWaveform PFC Zero Current Detect PFC Mosfet Gate Low Side Input High Side Input PFC Gate Driver 470n 275VAC OSC1/CLKIN/PC0 OSC2/PC1 PA0(HS)/LTIC PA1(HS)/ATIC PA2(HS)/ATPWM0 PA3(HS)/ATPWM1 PA4(HS)/ATPWM2 PA5(HS)/ATPWM3/ICCDATA PA6/MCO/ICCCLK/BREAK PA7(HS)/COMPOUT ICC-programmer 1 3 5 7 9 U1 D13 STTH1L06A RsenseCurrent Vss Vdd RESET COMPIN+/SS/AIN0/PB0 SCK/AIN1/PB1 MISO/AIN2/PB2 MOSI/AIN3/PB3 COMP-/CLKIN/AIN4/PB4 AIN5/PB5 AIN6/PB6 DC5V 1 2 3 4 5 6 7 8 9 10 1 RsenseCurrent 2x47mH 3 1 3k9 R27 T1 4 2 J4 jump-prog/run 10k R24 R2 1M 350V 4 + 2 BRIDGE RB156 CSO 4n7 1.8k R52 R21 10 R19 10 1k R14 R51 47k R47 47k RsenseCurrent 2 STTH1L06 D14 0.6W 0 R18 2n7 C5 C6 PFC OC NTC1 10 LampTypeDetection Circuit 1k Lamp Type Detection Circuit Enable 10n C14 1 PFC Vout Sense R10 CSO C13 50V 100nF CSI R9 0.5 2 STTH1L06 D2 STP6NK60Z 1 PFC Zero Current Detect DC5V Q1 1 R8 47k 1 8 1 D7 3 5 R1 1M 350V 1 2 3 1 2 2 3 C1 220n 275VAC R49 10k Q5 BF420 Q4 BF421 R13 10k R12 750k R11 750k 10k R54 22uF 450V C7 R23 1 2W,1% 1.2mH L1 C23 68n C30 330n R36 22k PeakLampVoltage Out pin R48 3.3k Vcap 470n C18 AverageLampVoltage LampTypeDetection Circuit Q3 STP6NK60Z Q2 STP6NK60Z + DC400V 1M R29 R40 2k2 R39 220k R38 220k 1N4148 SMD D6 C19 4n7 100V LampPresence DC5V LampTypeDetection C17 10n R30 10k R53 100nF 400V C15 75k R35 R41 2k2 1M DC5V R37 220k Vcap 1 4 FUSE 2 T5 Lamps 3 J2 R34 120k R33 330k R32 330k R31 330k Vcap C16 10n 1600V 6.1 F1 AN2640 Board description Electrical schematic Figure 25. Electrical schematic 25/36 Board description AN2640 6.2 Bill of materials Table 3. BOM Item Qty Reference Part / value Voltage Watt Type 275 Vac EPCOS - order code B32922C3224K 1 1 C1 220 nF 2 1 C10, C14 10 F 3 1 C11 47 µF 35 V Electrolytic 4 2 C12, C13 100 nF 50V Ceramic 5 2 C16 10 nF 1600 V EPCOS - order code B32653A1103J 6 1 C15 100 nF 400 V Polyester 7 1 C17 10 nF 50 V Ceramic 8 2 C18, C22 470 nF 50 V Ceramic 9 1 C19 4.7 nF 100 V Ceramic 10 1 C2 1 nF 275 Vac Y2 capacitor 11 1 C20 1 nF 50 V Ceramic 12 1 C23 68 nF 50 V Ceramic 13 3 C25, C26, C28 10 pF 50 V Ceramic 14 1 C27 10 pF 50 V Ceramic 15 1 C3 470 nF 275 Vac Polyester 16 1 C30 330 nF 50 V Ceramic 17 1 C4 100 pF 50 V Ceramic 18 1 C5 2.7 nF 50 V Ceramic 19 1 C6 4.7 nF 50 V Ceramic 20 1 C7 47 µF 450 V Electrolytic 21 1 C8 1 nF 630 Vdc Polyester 22 1 C9 220 nF 50 V Ceramic 23 1 D12 1N4007 1 A 1000 V General purpose rectifier 24 3 D2, D13, D14 STTH1L06A 1 A 600 V ST Microelectronics turbo 2 ultrafast high-voltage rectifier 25 2 D4, D6 1N4148 200 mA 100 V Small signal diode 26 1 D7 BRIDGE RB156 27 1 F1 Fuse 2 A, 250 V 28 1 L1 1.2 mH ± 5% 29 1 NTC1 10 30 3 Q1, Q2, Q3 STP6NK60Z 26/36 Ceramic Bridge rectifier 250 V VOGT PFC choke EVD25 Part nr. SL0606302101 1 Ω / 6 A 600 V STMicroelectronics Zener-protected SuperMESH™ MOSFET AN2640 Table 3. Item Qty Board description BOM (continued) Reference Part / value Voltage Watt Type 31 1 Q4 BF421 500 mA 300 V Small signal PNP transistor 32 1 Q5 BF420 500 mA 300 V Small signal NPN transistor 33 3 R1, R2, R29 1 MΩ 34 2 R10, R14 1 kΩ - 1% 35 5 R13, R24, R30, R49, R54 10 kΩ - 1% 36 2 R16, R46 22 Ω 37 1 R18 0Ω 38 1 R22 33 Ω 39 1 R23 1 Ω - 1% 40 1 R27 3.9 kΩ - 1% 41 1 R28 820 Ω - 1% 42 4 R3, R4, R11, R12 750 kΩ - 1% 43 3 R31, R32, R33 330 kΩ - 1% 0.25 W 44 1 R34 120 kΩ - 1% 0.2 5W 45 1 R35 75 Ω - 1% 0.25 W 46 1 R36 22 kΩ - 1% 47 3 R37, R38, R39 220 kΩ - 1% 0.25 W 48 1 R40 2.2 kΩ 0.25 W 49 1 R41 2.2 kΩ - 1% 50 3 R43, R44, R45 10 kΩ 51 1 R48 3.3 kΩ 52 1 R5 18 kΩ - 1% 53 1 R52 1.8 kΩ 54 1 R53 1 MΩ 55 1 R6 27 kΩ 56 3 R7, R19, R21 10 Ω 57 3 R8, R47, R51 47 kΩ 58 1 R9 0.5 Ω - 1% 59 1 T1 2x47 mH at 0.5 A EPCOS Current-compensated D core choke Or. code B82731-M2501-A30 60 1 T2 2 mH ± 5% VOGT PFC choke EVD25 Part nr. SL0606301101 0.6 W 1W 1W 27/36 Board description Table 3. Item Qty AN2640 BOM (continued) Reference Part / value Voltage Watt Type 61 1 U1 ST7FLIT19BF1B 6 STMicroelectronics 8-bit MCU 62 1 U2 L6382D5 STMicroelectronics power management unit for microcontrolled ballast 6.3 Experimental results 6.3.1 From system switch on to ballast run The identification tests have been performed using T5 tubes having 24, 39, 54 and 80 W lamp power ratings. Tests have been performed across the entire European mains (185 V ÷ 230 V / 50 Hz) input range. Figure 26. L6382 startup sequence and ballast start The following results have been obtained with 230 V at 50 Hz as mains. 28/36 AN2640 Board description Figure 27. 24 W lamp power Figure 28. 39 W lamp power 29/36 Board description AN2640 Figure 29. 54 W lamp power Figure 30. 80 W lamp power In Figure 27, 28, 29, and 30 it can be seen that the ballast identifies each lamp and that after the recognition phase it adjusts and regulates the half-bridge working frequency to supply the correct current to the lamp. 30/36 AN2640 6.3.2 Board description PF, THD and ballast efficiency The power factor, total harmonic distortion of current and ballast efficiency are measured and the results are shown in Table 4, 5, 6, and 7. Table 4. Mains PF THD η% 185 V at 50 Hz 0.968 17.6 88.2 230 V at 50 Hz 0.949 20.0 89.3 265 V at 50 Hz 0.923 22.0 89.9 Mains PF THD η% 185 V at 50 Hz 0.983 13.5 90.4 230 V at 50 Hz 0.970 15.7 90.6 265 V at 50 Hz 0.956 17.4 90.6 Mains PF THD η% 185 V at 50 Hz 0.989 11.3 94.1 230 V at 50 Hz 0.982 13.0 94.4 265 V at 50 Hz 0.972 14.4 94.6 Mains PF THD η% 185 V at 50 Hz 0.992 10.9 97.6 230 V at 50 Hz 0.988 11.1 98.0 265 V at 50 Hz 0.980 14.6 98.2 Table 5. Table 6. Table 7. 6.3.3 24 W lamp power 39 W lamp power 54 W lamp power 80 W lamp power Electromagnetic compatibility The EMC tests have been performed according to the EN55015 standard (Limits and methods of measurement of radio disturbance characteristics of electrical lighting and similar equipment). The Agilent E7401A EMC Analyzer has been used as test equipment. 31/36 Board description AN2640 Figure 31. Test equipment Agilent 6812B AC Power Source / Analyzer Agilent E7401A EMC Analyzer Figure 32, 33, 34, and 35 show the results. Figure 32. 24 W Figure 33. 39 W 32/36 STEVAL-ILB004V1 T5 Tube AN2640 Conclusion Figure 34. 54 W Figure 35. 80 W 7 Conclusion The proposed microcontrolled multipower ballast has several advantages. Design and production cost are reduced as there is no need for different circuits to drive different lamps. Moreover, by using the microcontroller, the systems' present flexibility from a design point of view respects that of an analog circuit. With the use of STMicroelectronics' Power MOSFET and diodes, the circuit shows good overall efficiency results. 33/36 References 8 34/36 AN2640 References 1. AN966: L6561, Enhanced Transition Mode Power Factor Corrector 2. STMicroelectronics ST7LITE1xB (8-BIT MCU with single voltage flash memory, data EEPROM, ADC, 5 Timers, SPI) datasheet 3. STMicroelectronics L6382D5 (Power management unit for microcontrolled ballast) datasheet AN2640 9 Revision history Revision history Table 8. Document revision history Date Revision 28-Jan-2008 1 Changes Initial release 35/36 AN2640 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. 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