ALSO IN THIS ISSUE: For more information contact: Graham Robertson Media Relations, FOR DESIGNERS AND SYSTEMS ENGINEERS

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1 JUNE 2009 Vol. 35, No. 6 FOR DESIGNERS AND SYSTEMS ENGINEERS ALSO IN THIS ISSUE: For more informaion conac: Graham Roberson Media Relaions, New PWM Slope Compensaion Techniques AC Power Tesing Challenges Power-Facor For Cable-Fed Moor Compensaing he RHPZ PoE SoC Manages Remoe Device Power A PENTON PUBLICATION

2 DESIGNfeaure Fluorescen Lamp Conrol IC Does Dimming wih TOM RIBARICH, Direcor, Lighing Sysems and Applicaions Only 8 Pins Inernaional Recifier, El Segundo, CA Wih dimming levels down o 10%, a new IC minimizes componen coun o improve dimming-circui speed, simplify design, and open up new dimming applicaions. DESIGNING DIMMING CIRCUITS FOR FLUORESCENT LAMPS is a challenging ask ypically realized using a complex, high-pin-coun conrol IC. Compared wih non-dimming designs, dimming circui ICs: Are more difficul o design so hey mee he required performance Require more componens Require more PC board area and layers Cos more There are several challenges associaed wih adding dimming funcionaliy o his IC wihou increasing pin coun. A novel conrol mehod overcomes his challenge wih a new DIM8 conrol IC for he general fluorescen lighing marke. The resul is an 8-pin dimming IC ha is simple and has a wide variey of applicaions. To undersand he deails behind he new dimming IC, we should firs look a he IR2520D, an exising 8-pin, nondimming ballas-conrol IC used in a vari-

3 L F1 AC LINE INPUT BR1 LF N RVCC1 RVCC2 CF CBUS RLIM1 CVCC1 RLIM2 CVCC2 RFMIN CVCO VCC 1 COM 2 FMIN IR2520D 3 VCO 4 VB 8 HO 7 VS 6 LO 5 RHO CBS RLO MHS MLS CSNUB DCP2 LRES CRES CDC SPIRAL CFL LAMP DCP1 Fig 1. Fluorescen lamp ballas circui using he non-dimming IR2520D conrol IC. ey of fluorescen lighing applicaions (Fig. 1). This IC only requires wo pins FMIN and VCO o conrol prehea, igniion and running requiremens of he lamp. The remaining pins perform sandard funcions such as IC supply and ground (pins VCC and COM), and high- and low-side gae drive for he half-bridge (pins LO, VS, HO and VB). When he ac line volage is firs applied o he circui, he volage across capacior CBUS charges up. Resisors RVCC1 and RVCC2 supply VCC wih he necessary micro-power curren o charge VCC up o he inernal UVLO+ hreshold. When VCC exceeds he UVLO+ hreshold, he IR2520D eners he frequency-sweep mode. The gae driver oupus (LO and HO) and he half-bridge circui (MHS and MLS) oscillae a he maximum frequency. The charge-pump circui (CSNUB, DCP1 and DCP2) akes over as he main supply circui for he IC and keeps VCC mainained a he inernal clamp volage of 15.6 V. A small inernal curren source a he VCO pin slowly charges up he exernal capacior (CVCO) causing he volage on pin VCO o ramp up linearly (Fig. 2). This causes he frequency of he gae-driver oupus and he half-bridge swiching circui o ramp down from he maximum saring frequency. As he frequency ramps down oward he resonance frequency of he high-q, under-damped oupu sage (LRES, CRES), he lamp volage increases (Fig. 3). The volage on pin VCO coninues o increase while he frequency keeps decreasing unil he lamp ignies. The oupu circui hen becomes an over-damped, low-q circui. The volage on pin VCO coninues o increase unil i exceeds 4.6 V and he IC eners run mode. The frequency sops decreasing when he VCO pin exceeds 5 V and says a he minimum frequency as programmed by an exernal resisor, RFMIN, on pin FMIN. Capacior CVCO ses he ime for preheaing he lamp filamens and sweep- V VCO 6 V 4.6 V 0.85 V Freq f max f min Frequency sweep mode Run mode Fig. 2. Frequency sweep mode iming diagram for he non-dimming IR2520D fluorescen lamp conrol IC.

4 FLUORESCENTdimming V ou V in Low-Q High-Q Run f min Igniion Sar ing he frequency for igniion, and resisor RFMIN ses he running frequency, which ses he correc lamp power during running. All he remaining faul-proecion circuis guard agains ac line brown-ou, lamp non-srike and filamen failures, which are inegraed ino he IC and require no addiional exernal componens. This IC is simple o use and requires minimal ime o design he complee elecronic ballas. Wih dimming now becoming more and more popular due o he increased energy savings, he challenge is o add V REF he dimming funcion o he IC wihou increasing pin coun and mainaining he simpliciy of he IR2520D. We always need a VCO pin o V REF + V RCS perform he necessary frequency sweep for prehea and igniion, so his leaves only he FMIN pin o be used for dimming conrol. SINGLE-PIN DIMMING CONTROL To dim he fluorescen lamp, he frequency is used o conrol he lamp curren. As he frequency of he half-bridge is increased, he gain of he resonan-ank circui decreases and he lamp curren also decreases. A closed-loop feedback circui is used o regulae he lamp curren o a dimming reference level by coninuously adjusing he half-bridge operaing frequency. The new dimming funcion is realized by combining he ac lamp curren measuremen (Fig. 4) wih a dc reference volage a a single Prehea f max Frequency Fig. 3. Resonan-ank Bode plo wih lamp operaing poins (sar, igniion, run) for he non-dimming IR2520D conrol IC. VREF R1 To DIM pin CFB CDIM V REF 100% RFB 100% dimming 10% dimming AC lamp curren RCS V REF 10% V RCS Fig. 4. Single-node ac+dc dimming-conrol mehod employed in he new IR2530D conrol IC. node. The ac lamp curren is measured across a sensing resisor, RCS, and coupled ono he dc dimming reference hrough feedback capacior CFB and resisor RFB. The feedback circui regulaes he valley of he ac+dc signal o COM as he dc dimming level is increased or decreased by coninuously adjusing he half-bridge frequency. This causes he ampliude of he lamp curren o increase or decrease for dimming. If he dc reference is increased, he valley of he ac+dc signal will increase above COM and he feedback circui will decrease he frequency o increase he gain of he resonan ank. This will increase he lamp curren, as well as he ampliude of he ac+dc signal a he DIM pin, unil he valley reaches COM again. If he dc reference is decreased, he valley will decrease below COM. The feedback circui will hen increase he frequency o decrease he gain of he resonan ank unil he valley reaches COM again. The FMIN pin of he IR2520D used o program a single running frequency has now been replaced wih he new DIM pin, which is used o measure he ac+dc signal for dimming. The new IRS2530D dimming-conrol IC is a complee 8-pin soluion ha includes all dimming ballas funcionaliy and proecs he circui agains lamp faul condiions. The IC already uses six pins for very basic bu necessary funcions: IC supply and ground (VCC, COM), and half-bridge high- and low-side gae drive (VB, HO, VS, LO). The VCO pin includes he frequency-sweep iming conrol for prehea and igniion, and also programs he loop speed for he dimming feedback circui during dim mode.

5 FLUORESCENTdimming V VCO Freq f max f min V LAMP Lamp ignies Prehea/Igniion mode. The half-bridge begins oscillaing a he maximum frequency and he inernal curren source a he VCO pin begins charging up an exernal capacior (CVCO) linearly from COM (Fig. 4). The oupu frequency decreases as he VCO volage increases and he lamp filamens are preheaed by secondary windings from he resonan ank inducor. As he VCO volage charges up, he frequency decreases oward he resonan frequency of he resonanank circui and he oupu volage across he lamp increases. The lamp ignies when he oupu volage exceeds he lamp igniion hreshold volage, lamp curren begins o flow, and he IC eners dim mode. Fig. 5 is he prehea, igniion and dimming iming diagram for he IR2530D. I LAMP Prehea/igniions Dimming Fig. 5. Prehea, igniion and dimming iming diagram for he new IR2530D conrol IC. When a volage is firs applied o VCC (14 V ypical) he IC exis UVLO mode and eners DIMMING MINI-BALLAST DESIGN A complee dimming mini-ballas circui (Fig. 6) was buil and esed o demonsrae performance. The circui runs from a 220-Vac line and drives a 25-W compac fluorescen lamp. The 220-Vac/50-Hz line-inpu-volage is fullwave recified (BR1) and goes hrough an EMI filer (CF and LF) before being smoohed by he dc bus capacior (CBUS). The half-bridge swiches (MHS and MLS) are conrolled by he new IRS2530D for preheaing, igniing and dimming he lamp. RVCC1 and RVCC2 provide he micro-power sar-up curren for he VCC supply RF1 0.47R 0.5 W L 220 V AC LINE INPUT N BR1 0.5 A 600 V LF 1 mh 200 ma RVCC1 360k RVCC2 360k Poeniomeer dimming inpu RMAX 200k 1% PDIM 10k po single urn RMIN 430R 1% CF 47 nf 400 V CBUS 10 μf 350 V VCC 1 CVCC COM 1 μf 2 CDIM 10 nf DIM IR2530D 3 CVCO 2.2 nf VCO 4 CPH 0.68 μf RVCO 1.5k CFB 0.1 μf RFB 1k VB RHO 8 10R HO 7 VS 6 LO RLO 10R 5 MHS IRFU320 CBS 0.1 μf CVS RLMP1 220k MHS IRFU320 1 nf 1 kv DCP2 1N4148 DCP1 18 V 0.5 W LRES A 2.3 mh EF20 airgap = 1 mm CDC 47 nf 400 V CRES 4.7 nf 1.6 kv RLMP2 470k LRES B 0.12 μh 5 urns CH1 LRES C 0.12 μh 5 urns CH2 25 W CFL LAMP RCS 7.5R/1% 1 W Fig. 6. Dimming fluorescen lamp mini-ballas circui for he IR2530D conrol IC.

6 FLUORESCENTdimming (a) Fig. 7. Mini-ballas measured waveforms. (a) VCO pin volage (upper race), lamp volage (middle race) and lamp curren (lower race) during normal prehea, igniion and dimming modes. (b) (b) Half-bridge oupu volage (VS pin, lower race) and DIM pin volage (upper race) during 100% dimming. (c) (c) Half-bridge oupu volage (VS pin, lower race) and DIM pin volage (upper race) during 10% dimming. of he IC, and he charge pump (CSNUB, DCP1 and DCP2) akes over as he IC supply once he half-bridge begins o oscillae. The resonan-ank circui (LRES and CRES) provides he necessary ransfer funcion for generaing high volages for lamp igniion and low-pass filering for dimming. A dc blocking capacior (CDC) ensures ha he lamp curren is always ac o preven mercury migraion, which can cause lamp-end blackening and a shorened lamp life. Secondary windings from he resonan inducor (LRES:A,B) are used o hea he lamp filamens during prehea and dimming, and also separae he lamp curren from he filamen curren allowing for a single curren-sensing resisor (RCS) o be used o sense he lamp curren. The ac lamp curren measuremen across RCS is coupled o he DIM pin hrough a feedback capacior and resisor (CFB and RFB). A poeniomeer dimming inpu circui is used (PDIM, RMIN, RMAX) o conver he poeniomeer resisance o he necessary dimming reference volage for he IC ha is conneced o he DIM pin. Finally, resisors RLMP1 and RLMP2 are used o deec if he lamp has been removed and o auomaically resar he ballas when he lamp is re-insered. Proecion agains all oher ballas faul condiions such as failure o srike, open filamen, and low ac line/brown-ou are included inernally o he IRS2530D o furher reduce componen coun and increase reliabiliy. The measured ballas waveforms are shown in Fig. 7. Fig. 7a shows he VCO pin volage (upper race), lamp volage (middle race) and lamp curren (lower race) during normal prehea, igniion and dimming modes. The VCO pin and lamp volage ramp up during prehea and igniion o prehea he lamp filamens and hen o ignie he lamp when he lamp igniion volage hreshold is reached. Lamp curren sars o flow immediaely afer igniion a he sar of dimming. Fig. 7b and 7c show he half-bridge oupu volage (VS pin, lower race) ogeher wih he DIM pin volage (upper race) during 100% and 10% dimming condiions. The DIM pin volage ampliude decreases (ogeher wih he lamp curren) from 100% down o 10% and he operaing frequency is coninuously adjused o keep he valley of he sinusoid regulaed a COM. The new IC delivers excellen dimming performance down o 10% dimming levels while minimizing componen coun. Copyrigh 2009 by Penon Media, Inc.