designfeature Andre Tjokrorahardjo Applications Engineer, Lighting Systems and Applications International Rectifier, El Segundo, Calif. Simple, Versatile Control IC Dims Fluorescent Ballasts F luorescent dimming systems can satisfy visual comfort, and reduce utility costs through daylight harvesting, demand reduction, scheduled dimming, and other strategies. A dimming electronic ballast is an essential part of this system. To perform dimming functions, the ballast must be configured to understand an input signal from the control device, and act upon the current flowing through the lamp. Typically, this is a challenging task for the ballast designer and is usually achieved using a complex, high-pin-count control IC. The IRS2530D is a new dimming ballast control IC in a compact 8-pin form-factor (Fig. 1). This DIM8TM is a 600-V half-bridge driver IC that includes all the necessary functions for preheat, ignition, and dimming control of the lamp, and protects the circuit against line and lamp fault conditions. With only eight pins to accomplish all dimming ballast functions, the IC can minimize component count and simplify design, and is flexible enough to be used with various dimming control methods. Several reference-design kits have been created to help with the evaluation of the IRS2530D. Each of these kits uses a different dimming control method, and they cover various input voltages and lamp types. A complete description of each kit is available at International Rectifier’s lighting website (www.irf.com/product-info/lighting/). The IRS2530D is simple to use with any analog and digital control method available for dimming fluorescent lamps. In addition, it can implement dimming control for LEDs. Power Line Communication Analog Dimming Fig. 2 shows the schematic of a dimmable 3-Way electronic ballast for driving a 26-W quad-pin CFL from a Wireless IR CFL 220-Vac line with an isolated 1- to 10-Vdc dimming input. The Triac ballast comprises an Dimming Wall EMI filter to block balInterface Dimmer last-generated noise, Linear Fluorescent a rectifier and bus capacitor to convert ac line input into a dc bus 0 to 10 V Analog voltage, a control IC and half-bridge to proDigital duce high-frequency square-wave voltage, LED Switch and a resonant output Fig. 1. The IRS2530D is a 600-V half-bridge driver IC with all the necessary functions for preheat, ignition, and stage for preheating, dimming control of the lamp. Plus, it protects the circuit against line and lamp fault conditions. igniting, and running 0° 1° 2° 3° L1 L2 N 1 0 10 0 1 0 1 1 1 26 Power Electronics Technology | March 2010 Reprinted by permission of Power Electronics Technology magazine. www.powerelectronics.com dimmingcontrollers L RF1 0.47 R 0.5 W 220 Vac Line Input Full-Bridge Rectifier EMI Filter LF 1 mH 0.2 A BR1 600 V 0.5 A RVCC1 360 k N RVCC2 360 k Bus Cap CF 47 nF 400 V D2 1N4148 D1 11 V VCC 1 0.1 µF COM CVCC2 2 CDIM 10 nF DIM 3 CVCO 2.2 nF VCO 4 CPH 0.68 µF D4 RVCO 1N4148 1.5 k R4 15 k D3 1N4148 T1 2x30 mH R1 100 k R2 470 k R3 1.8 k C2 0.1 µF Half-Bridge Control IC RLIM2 10 R IRS2530D DC Dimming Reference Input + 1 to 10 V C1 DIM INPUT 0.1 µF - CBUS + 10 µF RLIM1 350 Vdc 10 R 1 µF CVCC1 CFB 0.1 µF VB 8 HO 7 VS 6 LO 5 RHO 10 R MHS IRFU320 LRES: A 2.3 mH CBS 0.1 µF RLO 10 R MLS IRFU320 CVS 1 nF 1 kV CSNUB 1 nF 1 kV DCP2 1N4148 RVS2 82 k EF20 airgap = 1 mm CDC 47 nF 400 V LRES:B 5 turns CRES 4.7 nF 1.6 kV OSRAM DULUX T/E 26 W/840 CH1 0.18 µF RLMP2 470 k CH2 0.18 µF DCP1 18 V 0.5 W RLMP1 220 k RFB 1k Resonant Output Tank LRES:C 5 turns RCS 7.5 R RVS1 82 k Isolation Current Sensing Fig. 2. The ballast contains an EMI filter, rectifier, bus capacitor, control IC, and half-bridge to produce high-frequency square wave voltage, and a resonant output stage for preheating, igniting, and running the lamp. the lamp. The current-sensing resistor and the isolated dimming reference input are additional components needed for dimming application. The IRPLDIM4E reference design kit does not include the isolation section of the circuit. X1A L 220 V AC Line Input N X1B RF1 0.47 R 0.5 W DC Reference Generator for Quad-Level Switch Dimming System LF 1 mH/200 mA CF 0.1 µF 275 Vac When power is initially turned on, the bus capacitor (CBUS) charges up, and resistors RVCC1 and RVCC2 supply the micro-power current to the IRS2530D. After the VCC voltage reaches above UVLO threshold, the half- R3 120 k BR1 600 V 0.5 A C3 10 n R1 150 k R2 150 k DIN 600 V 1A C2 0.1 µF C1 330 µF R9 100 k VDD 1 P2 2 P3 3 P4 4 RVCC1 360 k R5 24 k D2 5.1 V RVCC2 360 k VSS 8 P7 7 P6 6 P5 5 R6 10 M + R7 100 k C7 0.1 µF VCC 1 CVCC COM 1 µF 2 CDIM 10 n DIM 3 CVCO 2.2 n VCO 4 CPH 0.68 µF IC1 IRS2530D R10 100 k C6 2.2 µF IC2 PIC12F629 D1 5.1 V CBUS 10 µF 350 V R4 120 k RVCO 1.5 k R8 56 k VB 8 HO 7 VS 6 LO 5 RHO 1O R CBS 0.1 µF RLO 10 R RLMP1 470 k CFB 0.1 µF RFB 1k MHS IRFU320 LRES:A 2.3 mH CDC EF20 47 n airgap = 1 mm 400 V LRES:B Five turns CVS 1n 1 kV MLS IRFU320 CRES 4.7 n 1,600 V DCP1 1N4148 RLMP2 1M DCP1 17 V 0.5 W 26 W CFL Lamp CH1 0.1 µF CH2 0.1 µF LRES:C 5 turns RCS 7.5 R 1% Fig. 3. The IRPLDIM5E is a quad-level switch-dimming fluorescent ballast that operates from a 220-Vac line and drives a 26-W quad-pin CFL. www.powerelectronics.com March 2010 | Power Electronics Technology Reprinted by permission of Power Electronics Technology magazine. 27 dimmingcontrollers Voltage Doubler DC Reference Generator for 3-Way Dimming System BR1:D1 DF10S BR1:D2 DF10S RPU 220 k LF 1 mH C3 47 µF 200 V PL 1 CF 0.068 µF 400 V RSUPPLY 1M RVCC1 11 R RVCC2 11 R CVCC1 2.2 µF R3 1M PL 2 0 1 Live 30 1 2 C2 0.1 µF C1 250 V 0.1 µF 250 V Common 3 3-Way Socket Screw Base Neutral Q3 MMBTA42 Q4 MMBTA42 R4 1M R6 1M RPU 0.47/0.5 W DZI 68 V Q1 STP7NK40Z CVCC2 0.1 µF CDIM 0.01 µF CVCO 2.2 n R5 220 k C4 47 µF 200 V BR1:D3 DF10S BR1:D4 DF10S CPH 0.47 µF VCC VB 8 1 COM 2 DIM 3 VCO IRS2530D 120 V AC Line 2 R17 1 M R7 1k RDIM C5 10 k 10 µF CFB 0.1 µF VS 6 LO 5 4 RVCO 1.5 k HO 7 RFB 1k RHO 11 R CBS 0.1 µF RLO 11 R Q2 STP7NK40Z RLMP1 100 k RLMP2 1M CSNUB 1 n/1 kV DCP2 1N4148 DCP1 1N4148 LRES:A 2.2 mH EF20 CDC airgap 47 n/ = 1 mm 400 V CRES 4.7 n/1.6 kV LRES:B 5 Turns CH1 220 µF 32-W Spiral CFL Lamp CH2 220 µF LRES:C 5 Turns RCS 8.2 R/1%/1 W Fig. 4. The IRPLCFL8U is a three-way switch-dimming electronic ballast driving a 32-W spiral CFL from a 120-Vac line. bridge starts to oscillate at the maximum frequency. The charge-pump circuit (CVS, DCP1, and DCP2) takes over as the main supply circuit for the IC and keeps the VCC at the internally clamped 15.6 V. An internal current source at the VCO pin charges up the external capacitor (CPH). Output frequency decreases as the CPH charges and, at the same time, the lamp filaments are preheated using the secondary winding from the resonant inductor. As the frequency decreases toward the resonant frequency of the output stage, the voltage across the lamp increases. After it reaches a high enough voltage to ignite the lamp, lamp current begins to flow. The resonant output stage transitions to a series-L, parallel RC circuit with the Q-value and operating point determined by the user’s dim level. Ac lamp current is sensed by the resistor RCS, and the resulting ac voltage is coupled with the dc dimming reference voltage from isolation through feedback resistor (RFB) and feedback capacitor (CFB). This dc + ac signal is then fed into the DIM pin of the IRS2530D and is regulated by the control loop, such that the valley of the ac voltage always stays at COM. When the dc reference voltage at the DIM pin is decreased for dimming, the valleys of the ac voltage are pushed below COM. The dimming control circuit increases the frequency to decrease the gain of the resonant tank circuit, and thus the ac lamp current, until the ac valleys at the DIM pin are at COM again. The opposite happens when the dc reference is increased to increase the brightness level. In this way, the dimming control circuit keeps the ac lamp current peak-to-peak amplitude regulated to the desired value at all dc dim level settings. Quad-Level Switch Dimming Another dimming control method is quad-level switch dimming, which uses the on/off switch to control the dimming level. When the switch is turned off and then turned back on in less than one second, the dimming level is reduced by one level. If the dimming level is already at the minimum, this action will cycle the dimming level back to the maximum. If the switch is turned off for more than one second, dimming will stay at the last level. The IRPLDIM5E is a quad-level switch-dimming fluorescent ballast which drives a 26-W quad-pin CFL from a 220-Vac line. Fig. 3 shows the schematic of the IRPLDIM5E. The circuit in Fig. 3 is similar to the IRPLDIM4E, except for the circuitry to generate the dc dimming reference voltage. A microcontroller is used to provide the reference voltage and to determine whether to switch to the next dimming level. The micro-controller used here is the PIC12F629, which contains some EEPROM non-volatile memory that allows the microcontroller to store the last dim level setting before shutting down after power is switched off. This enables the ballast to start up at that same setting when power is restored, no matter how long the ballast has been off. Pin 5 of the microcontroller generates a fixed-frequency square wave signal with four different duty cycles, which correspond to four dimming levels. The square wave signal 28 Power Electronics Technology | March 2010 Reprinted by permission of Power Electronics Technology magazine. www.powerelectronics.com dimmingcontrollers then goes through the low-pass filter to produce the dc reference voltage. Pin 6 of the microcontroller is connected to the bridge rectifier through a filter circuit with a very short delay. This allows the microcontroller to detect when ac power has been removed and restored quickly. The VDD supply capacitor, C1, is large enough to allow the microcontroller to continue to run for more than one second after ac power has been removed from the ballast. The microcontroller starts a timer as soon as it detects that the power is switched off. If power is restored within one second, the microcontroller will reduce the duty cycle one level, and thus reduce the dc reference by one step. If the level is already at the minimum, it will cycle back to the maximum duty cycle. filaments are connected. In the second position, the first filament (PL1) is connected across the ac line for the lowest brightness setting. Resistor R5 pulls up the dc dimming reference across resistor R7 and capacitor C5 to set the minimum brightness. The third position, which corresponds to the medium brightness setting, uses R6 to pull up the dc dimming reference. In the fourth position, parallel resistors R5 and R6 set the dc dimming reference for the high brightness setting. The level of brightness can be modified as needed by changing the value of R5, R6, and R7. Transistor Q3 and Q4 ensure that the dc reference voltage is high enough at the high brightness, setting since both of these transistors will be switched on in this case. Phase-Cut (Triac) Dimmer Three-Way Switch dimming Virtually all domestic and professional dimming systems are based on triacs, also known as phase-cut dimmers. These devices conduct once they have been fired, only while the current flows in excess of the holding current of the device. These dimmers work very well with a resistive load—such as an incandescent light bulb—as the triac continues to conduct after it is fired, until very close to the end of the half-cycle. A traditional CFL ballast, in which there is no power factor correction, only draws current from the mains near the peak of the mains voltage where the storage capacitor charges—and not during the remainder of the mains halfcycle. The inability of traditional CFL ballasts to sustain conduction of the triac will cause severe flickering when used with such a dimmer. The three-way dimming system is widely adopted in the U.S. The system consists of a special lamp socket that has a four-position switch and a bulb with a modified screw base. For incandescent lamps, the bulb has two filaments and two connections on the lamp screw base. The IRPLCFL8U is a three-way switch-dimming electronic ballast driving a 32-W spiral CFL from a 120-Vac line. Fig. 4 shows the ballast, together with the three-way socket and the modified lamp base. The interface circuit includes a voltage doubler (D1, D2, D3, D4, C1, and C2) in place of a rectifier and a circuit to generate the dc dimming reference voltage (R3, R4, R5, R6, R7, RPU, Q3, Q4, DZ1, and C5). The first socket switch position is “off,” in which no F1 0.47 R 0.5 W L 120 V Triac Input C1 33 nF 250 V D1 600 V 1A L1 2.7 mH 0.15 A C2 33 nF 250 V D4 D2 RVCC1 100 k C4 6.8 nF 1 kV D3 RVCC2 100 k C3 33 nF 250 V C5 4.7 nF 1 kV N + VCC COM 2 R2 100 k R3 100 k CDIM 10 µF D5 1N4148 D6 10 V 0.5 W DIM 3 R4 100 k VB 8 1 CVCC 1 µF CVCO 2.2 µF VCO IRS2530D CBUS 22 µF 200 V C6 1.0 µF R6 15 k CPH 0.68 µF RHO 10 R HO 7 VS 6 LO RLO 10 R RVCO 1.5 k RLMP1 220 k CFB 0.1 µF RFB 1k MHS IRFU320 CBS 0.1 µF 5 4 R5 100 k Triac Interface LRES 1.25 mH 1A CVS 1 µF 1 kV MLS IRFU320 DCP2 1N4148 DCP2 10 V 0.5 W CDC 47 nF 400 V CRES 4.7 nF 1.6 kV LRES:B CH1 0.1 µF CFL Lamp CH2 0.1 µF LRES:C RCS 7.5 R/1 W 1% DC Reference Generator for Triac Dimming System Fig. 5. A triac-dimmable CFL ballast driving a single 15-W spiral CFL from a 120-Vac input. www.powerelectronics.com March 2010 | Power Electronics Technology Reprinted by permission of Power Electronics Technology magazine. 29 dimmingcontrollers Application note AN-1153 describes a triac-dimmable CFL ballast driving a single 15-W spiral CFL from a 120-Vac input. Fig. 5 shows the schematic of the ballast. Capacitors C2, C3, C4, and C5 are used to interface with the triac in the dimmer so that the ballast can maintain triac conduction until almost the end of the mains half-cycle. There is also circuitry that detects the firing angle of the triac and adjusts dc reference voltage to set the lamp current. The voltage waveform at the junction of D1 and D4 is equivalent to the output voltage of the dimmer. This will be a phase-cut approximated sine wave with a dc offset, such that the negative peak is at ground. This is reduced by the voltage divider network of R2 and R3, which is then fed into D5 and D6. Only the signal representing the positive half-cycle of the mains is left at the anode of D6, which is then converted to a dc level via the filter of R4 and C6. Because the minimum dimming level occurs at a point where the dimmer is still capable of providing enough output for the ballast to operate, this voltage will never actually be zero. The dc level is further reduced with the voltage divider network of R5 and R6, and used as the dc dimming reference voltage. digital dimming systems are relatively new. Because of the simplicity of its dimming control method, the IRS2530D can be easily utilized for both methods. The ballast designer needs to determine how to generate the proper dc voltage reference from the dimming control method being used. Analog dimming methods include 0- to 10-Vdc, phase-cut dimmers, and three-wire phase controls, as well as photo-sensor, motion-sensor, and wireless infrared. The dc voltage reference can be generated by a voltage divider using a combination of resistors, photoresistors, potentiometers, or rheostats. The dc voltage reference should be properly set, as it should not be too high to limit power loss in the currentsense resistor, and not too low to avoid noise problems at the minimum dimming level. The IRS2530D datasheet (www. irf.com/product-info/datasheets/data/irs2530d.pdf) explains how to properly set the dc reference and the current sense resistor. Digital dimming offers a number of advantages compared to analog: simplified wiring, a high degree of granularity for control accuracy, and two-way communication. Another advantage of this system is its capability to perform logarithmic dimming level. Since the human eye is much more sensitive to lower rather than higher light levels, the logarithmic light output appears to be linear. The most prominent of digital dimming methods is the open-standard two-wire interface digital addressable lighting interface (DALI). To work with digital dimming methods, Digital dimming offers a number of advantages compared to analog methods, including simplified wiring, a higher degree of control accuracy, and twoway communication Other Dimming Systems There are various dimming control methods available for fluorescent applications. In general, dimming control can be categorized into two methods: analog and digital. While analog dimming systems are well-established and common, L RF1 0.47 R 0.5 W 120 V AC Line Input LF 1 mH 0.2 A BR1 600 V 0.5 W RVCC1 360 k N CF 47 nF 400 V CBUS 10 µF 350 Vdc LED Current Reference Setting RVCC2 360 k Modified Output Stage for LEDs RLIM1 10 R RLIM2 10 R 1 µF CVCC1 0.1 µF CVCC2 COM CDIM 10 nF DIM CVCO 0.1 nF VCC VB 2 3 VCO RHO 10 R 8 1 IRS2530D DC Dimming Reference Input + HO 7 VS 6 CBS 0.1 µF LO 5 4 REMAX 200 k RLMP1 220 k RPOT1 10 k RMIN 430 R CFB 0.1 µF RLO 10 R LRES:A 2.3 mH EF25 airgap = 1mm MHS IRF730 MLS IRF730 CSNUB 1 nF 1 kV DCP2 1N4148 CRES 4.7 nF 1.6 kV D1 MUR160 D2 MUR160 D4 MUR160 D3 MUR160 6 HBLEDs 750 mA DCP1 18 V 0.5 W RFB 1k RCS 2.5 R/1 W 1% Fig. 6. The IRS2530D ballast can be used to control and dim the current of an offline LED. 30 Power Electronics Technology | March 2010 Reprinted by permission of Power Electronics Technology magazine. www.powerelectronics.com dimmingcontrollers a dimming ballast designed around the IRS2530D requires a microcontroller to communicate with digital protocols. The microcontroller interprets data from the digital control, and generates the square wave signal with fixed frequency but varying duty-cycle, which corresponds to the desired dimming level. Dimmable LED Drivers The dimming control loop of the IRS2530D keeps the amplitude of the LED current regulated by adjusting the frequency of the half-bridge switching circuit Unlike a fluorescent lamp, an LED requires constant current control and does not need to be preheated or ignited. The IRS2530D can also be used to control and dim LED current. Fig. 6 shows the schematic of an offline LED driver using the IRS2530D. The circuit is a resonant-mode circuit that has been slightly modified from the IRPLDIM4E circuit. Since it is no longer necessary to preheat and ignite the load, the output stage has been modified to become a series L-C-LED configuration. The resulting square-wave ac voltage at the output is converted to positive full wave rectified voltage using an additional full-bridge rectifier. Ac current sensing is still performed by the current-sensing resistor (RCS). This provides a direct ac measurement of the full wave rectified LED current amplitude. This ac signal is then coupled with the dc voltage from the current reference setting onto the DIM pin of the IRS2530D. The dimming control loop of the IRS2530D keeps the amplitude of the LED current regulated by continuously adjusting the frequency of the half-bridge switching circuit, such that the nominal rms LED current is maintained within the manufacturer’s specifications. When the dc reference voltage is decreased for dimming, the IRS2530D increases the frequency to decrease the gain of the resonant tank circuit and thus decrease LED current. This control scheme keeps LED current constant over line, load, and temperature variations for any given dimming reference input, and will work for any number of LEDs in series. The above LED control circuit is almost similar to the IRPLDIM4E dimming fluorescent ballast circuit. Any of the dimming fluorescent ballast methods described above can be easily translated to an LED control circuit. The dimming control loop of IRS2530D allows the circuit to be scaled to any number of LED in series. To work with LEDs with different current ratings, the current-sense resistor and dc reference settings need to be adjusted accordingly. www.powerelectronics.com March 2010 | Power Electronics Technology Reprinted by permission of Power Electronics Technology magazine. 31