3.5 W Non-isolated Offline Constant-current LED Driver .
AN2811Application note3.5 W non-isolated offline constant-current LED driverbased on VIPER17IntroductionHigh brightness LEDs are becoming a prominent source of lighting. Compared toconventional incandescent bulbs, high brightness LEDs (light emitting diodes) haveadvantages in higher light efficacy, much longer life and faster reaction time in a smallerprofile. Since LEDs cannot sustain high voltage stress directly from an AC source, providinga reliable constant-current source to drive LEDs becomes fundamental. This solutionprovides even luminosity, reliability, the highest efficacy and the longest operating life forLEDs.This application note describes the non-isolated offline constant-current driver based on theVIPER17HN (high frequency version). This solution operates with an AC line input rangefrom 176 V to 264 VAC and provides 500 mA constant current from a 7 VDC source. It canilluminate two LEDs in series.This device is an offline converter with an 800 V rugged power section, a PWM control,twice the level of overcurrent protection, overvoltage and overload protections, hystereticthermal protection, soft-start and also safe auto-restart after any fault condition removal.The embedded brownout function protects this switch mode power supply in case the maininput voltage falls below the specified minimum level for this system.Figure 1.STEVAL-ILL017V1 demonstration board !- V June 2009Doc ID 14904 Rev 11/25www.st.com
ContentsAN2811Contents1Safety instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52Design considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62.13Selected topology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6General circuit description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83.1Schematic diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83.2Bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93.3PCB layout view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113.4Transformer design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114Test results and waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135Connection of AC line and LED lamp to the demonstration board . . 216Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242/25Doc ID 14904 Rev 1
AN2811List of tablesList of tablesTable 1.Table 2.Table 3.Table 4.Table 5.Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6Bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Basic electrical characteristics of flyback transformer (T1). . . . . . . . . . . . . . . . . . . . . . . . . 11Bobbin dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24Doc ID 14904 Rev 13/25
List of figuresAN2811List of figuresFigure 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.Figure 36.4/25STEVAL-ILL017V1 demonstration board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1Conventional buck converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6Modified buck converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Flyback converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Schematic diagram of demonstration board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Top view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Bottom view with SMD parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Winding structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Bobbin outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12Efficiency versus input voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Standby power versus input voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Vin and Iin at 176 VAC, one LED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14Vin and Iin at 176 VAC, two LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14Vin and Iin at 264 VAC, one LED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14Vin and Iin at 264 VAC, two LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14Inrush current at LINE IN, one LED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15Inrush current at LINE IN, two LEDs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15Vds and Id at 176 VAC, one LED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16Vds and Id at 176 VAC, two LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16Vds and Id at 264 VAC, one LED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16Vds and Id at 264 VAC, two LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16Vo and Io at 176 VAC, one LED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17Vo and Io at 176 VAC, two LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17Vo and Io at 264 VAC, one LED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17Vo and Io at 264 VAC, two LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17Startup of Vo and Io at 176 VAC, one LED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18Startup of Vo and Io at 176 VAC, two LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18Startup of Vo and Io at 264 VAC, one LED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18Startup of Vo and Io at 264 VAC, two LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18Vdd and Vds at 264 VAC, output in short-circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19Io at 264 VAC, output in short-circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19Vdd and Vds at 264 VAC, output in open-circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20Startup of Vdd and Vds at 264 VAC, output in open-circuit . . . . . . . . . . . . . . . . . . . . . . . . 20Completed demonstration board connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21Connection of AC line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21Connection of LED lamp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21Doc ID 14904 Rev 1
AN28111Safety instructionsSafety instructionsWarning:The demonstration board must be used in a suitablelaboratory by only qualified personnel who are familiar withthe installation, use, and maintenance of electrical systems.Intended useThe demonstration board is a component designed for demonstration purposes only, andshall be used neither for domestic installation nor for industrial installation. The technicaldata as well as the information concerning the power supply and working conditions shall betaken from the documentation included with the demonstration board and strictly observed.InstallationThe installation of the demonstration board shall be taken from the present document andstrictly observed. The components must be protected against excessive strain. In particular,no components are to be bent, or isolating distances altered during the transportation,handling or usage. The demonstration board contains electro-statically sensitivecomponents that are prone to damage through improper use. Electrical components mustnot be mechanically damaged or destroyed (to avoid potential risks and health injury).Electrical connectionApplicable national accident prevention rules must be followed when working on the mainspower supply. The electrical installation shall be completed in accordance with theappropriate requirements (e.g. cross-sectional areas of conductors, fusing, and PEconnections).Board operationA system architecture which supplies power to the demonstration board shall be equippedwith additional control and protective devices in accordance with the applicable safetyrequirements (e.g. compliance with technical equipment and accident prevention rules).Doc ID 14904 Rev 15/25
Design considerationsAN28112Design considerations2.1Selected topologyThis is a 500 mA constant-current source conversion from 176 VAC 264 VAC line input.The specifications shown in Table 1 are for refrigerator lighting usage.Table 1.SpecificationsParameterValueAC input220 VAC 20%Output current500 mAOutput voltage7 V maxDimensions30 mm x 30 mmIsolationNot requiredTopologyConstant-current sourceAccording to the specifications the maximum operating power is 3.5 watts. No power factorcorrection circuit is required. Therefore, both buck and flyback topologies are suitable for thisapplication. Figure 2 shows the conventional buck converter while Figure 4 illustrates theflyback converter. To convert high voltage to low voltage, a conventional buck converter justrequires a few components. Output current ripple is small due to Vout obtained frominherent filter L1 and C1, thus the voltage and current stresses on these power componentsare small. In order to properly drive the MOSFET (Q1), a controller and an additionaltransformer are required. Additional winding with L1 to bias Q1 as well as a feedback currentto manage output in constant-current mode are needed.Figure 2.Conventional buck converter!- V 6/25Doc ID 14904 Rev 1
AN2811Design considerationsFigure 3.Modified buck converter!- V For ease in driving Q1 using a conventional buck converter, a modified buck converter hasbeen introduced as shown in Figure 3. Such topology is widely used to drive LEDs. With thismodified solution, the MOSFET is no longer floating. In this case the output (Vout) is notconnected to ground, and it becomes quite difficult to sense the output current in the outputstage directly. Compared to a buck converter, the flyback converter may be the betterchoice. Figure 4 shows the typical circuit of a flyback converter.Figure 4.Flyback converter!- V The auxiliary winding can be added to the transformer (T1) to provide bias for Q1. Unlike thebuck converter, T1 provides isolation between Vin and Vout. Since such isolation is notrequired for this application, a current sense resistor can be placed across the primaryground and negative polarity of Vout. Thus, Vout shares the same primary ground. In thistopology, the MOSFET is not floating. Thanks to VIPer17 the board is built with a highperformance low-voltage controller chip with an 800 V avalanche rugged power MOSFET.Designed with VIPer17, only a few external components are required which allows a smallerprofile in the design.Doc ID 14904 Rev 17/25
General circuit descriptionAN28113General circuit description3.1Schematic diagramFigure 5 shows the complete schematic diagram of the demonstration board. It consists ofan input full-bridge rectifier with filtering circuit, flyback converter and output stage.Figure 5.Schematic diagram of demonstration boardAM01057v18/25Doc ID 14904 Rev 1
AN2811General circuit descriptionReferring to the schematic diagram in Figure 5, fuse1 is the input fuse to prevent hazards ifthe system current exceeds the fuse rating. D1 is the bridge rectifier to convert AC to DC.The filter is formed by C11, L2 and C3 that are used to attenuate the high frequencyharmonic interference. T1 is the flyback transformer and U1 is formed by the PWM controllerand output MOSFET. The auxiliary winding (pin 5 and 6) and diode D5 provide bias supplyfor each control circuit. The output stage includes D6, C9 and C13. R9 and R12 are theoutput current sense resistors providing current sense signal. These are connected inparallel to share the power dissipation.The constant-current control circuit consists of U2, Q1, U1 and some passive components.The output current sense signal feeds to OP amp in U2. R7 and C7 consist of thecompensation network for the output signal of U2 in order to properly drive Q1. The 0.3 Vreference voltage on pin 6 of U2 is obtained by voltage divider R11 and R10. The collectorjunction of Q1 is connected to the feedback pin of U1 and completes the feedback loop.The output voltage is indirectly monitored by the auxiliary winding (pin 5 and 6 of T1) andfeedback to pin 3 of U1 through R1 and R4. Once the voltage at pin 3 of U1 exceeds 3 V, U1shuts down, then enters the auto-restart mode. Thanks to U1, which includes an overloadprotection function, if the LED is absent in the application (no load), this solution provides asafeguard. The LED and the application board are both fully protected.3.2Bill of materialTable 2.Bill of materialNameValueRatedTypeC11 nF25 VCeramic cap [0603]C2, C8100 nF25 VCeramic cap [0603]C3, C112.2 μF400 VAl elcap CAPPR3.5-8X12C456 nF25 VCeramic cap [0603]C5, C1210 μF25 VAl elcap CAPPR2-5X11C62.2 nF25 VCeramic cap [0603]C712 nF25 VCeramic cap [0603]C9220 μF16 VAl elcap CAPPR3.5-8X11.5C10470 pF25 VCeramic cap [0603]C131 μF25 VCeramic cap [0805]D1MB6S PKG30 E31 A 600 V bridge rectifierVishayD3BAT46JFILMSmall signal Schottky diode STMicroelectronics [SOD323]D5STTH1R06A1 A 600 V ultrafast rectifierSTMicroelectronics [SMA]D6STPS2H100A2 A 100 V Schottky rectifierSTMicroelectronics [SMA]Fuse1500 mA 250 VFuse 5 8.5*8 BelL2LPS3314-105ML1 mH, 0.1 AInductor, Coilcraft L LP3314Q1BC817-40NPN general-purposetransistor[SOT-23]R1240 kΩ1%Resistor [0603]Doc ID 14904 Rev 19/25
General circuit descriptionTable 2.AN2811Bill of material (continued)NameValueRatedTypeR26.8 kΩ1%Resistor [0603]R3100 kΩ1%Resistor [0603]R456 kΩ1%Resistor [0603]R510 kΩ1%Resistor [0603]R610 Ω1%Resistor [0603]R782 kΩ1%Resistor [0603]R83 kΩ1%Resistor [0603]R9, R121.2 Ω1%Resistor [1206]R103.3 kΩ1%Resistor [0603]R1124 kΩ1%Resistor [0603]R132.7 kΩ1%Resistor [0603]R141 MΩ1%Resistor [0603]T EE10/11 TDK1 mHTDK flyback transformerU1VIPER17HNOffline high voltageconverterSTMicroelectronics [DIP-7]U2TSM103WDual OP and voltagereferenceSTMicroelectronics [SO-8]T1(1)1. T1, the transformer design, is shown in Section 3.4 on page 11. Table 3 gives the basic electricalcharacteristics, Figure 8 shows the winding structure, and Figure 9 illustrates the bobbin outline.10/25Doc ID 14904 Rev 1
AN28113.3General circuit descriptionPCB layout viewThe PCB views are shown in Figure 6 and Figure 7.Figure 6.Top viewFigure 7. Bottom view with SMD parts !- V 3.4!- V Transformer designTable 3.Figure 8.Basic electrical characteristics of flyback transformer (T1)NameValueCore typeEE10/11-PC40Bobbin typeBE10-118CPSFRPrimary inductance1 mH /- 10%Leakage inductance10 µH typicalWinding structure!- V Doc ID 14904 Rev 111/25
General circuit descriptionFigure 9.AN2811Bobbin outline!- V Table 4.12/25Bobbin dimensionsDimensionValueA7.2 mmB3.5 mmC6.6 mmE3.85 mmX10.2 mmY10.2 mmZ9 mmP0.5 mmDoc ID 14904 Rev 1
AN28114Test results and waveformsTest results and waveformsFigure 10 shows the overall efficiency versus a range of AC line voltage loads with one LEDand two LEDs. Under both load conditions, we can observe that the efficiency drops wheninput voltage increases. The maximum efficiency occurs at minimum AC line input(176 VAC). Comparing a load condition of one LED with a load condition of two LEDs inseries, the efficiency increases by 7%. The efficiency with 1 LED is close to 75%.Figure 10. Efficiency versus input voltage!- V Figure 11 shows us the standby power which is measured when the LED is disconnected.Standby does not mean burst mode under light load. In standby, the overvoltage protectionworks. Under various AC line inputs, the maximum standby power is 0.18 W at 264 V input.Figure 11. Standby power versus input voltage!- V With the aid of the filter formed by C11, L2 and C3, no high-frequency interference can beobserved at the input current which definitely helps in meeting the conducted EMI standard.In Figure 12 and Figure 13 the waveform is captured at 176 VAC. In Figure 14 and Figure 15the waveform is captured at 264 VAC.To choose the proper rating of the fuse, we always refer to the inrush current. There are twoinrush current plots at the AC line input 220 V: Figure 16 with one LED and Figure 17 withtwo LEDs.Doc ID 14904 Rev 113/25
Test results and waveformsAN2811Figure 12. Vin and Iin at 176 VAC, one LEDFigure 13. Vin and Iin at 176 VAC, two LEDs !- V !- V Top trace: Vin (200 V/div)Top trace: Vin (200 V/div)Bottom trace: Iin (200 mA/div)Bottom trace: Iin (200 mA/div)Time: 4 ms/divTime: 4 ms/divFigure 14. Vin and Iin at 264 VAC, one LEDFigure 15. Vin and Iin at 264 VAC, two LEDs !- V !- V Top trace: Vin (200 V/div)Top trace: Vin (200 V/div)Bottom trace: Iin (200 mA/div)Bottom trace: Iin (200 mA/div)Time: 4 ms/divTime: 4 ms/div14/25Doc ID 14904 Rev 1
AN2811Test results and waveformsFigure 16. Inrush current at LINE IN, one LED Figure 17. Inrush current at LINE IN, two LEDs !- V !- V Iin: 5 A/div, 40 us/divIin: 5 A/div, 40 us/divMax. value: 14.2 AMax. value: 20.28 ADoc ID 14904 Rev 115/25
Test results and waveformsAN2811The VIPer17 integrates one 800 V MOSFET and the drain current is limited at 0.6 A. Thedrain-source voltage and drain current waveforms are shown in Figure 18 through 21. InFigure 18 and Figure 19 the waveform is captured at 176 VAC. In Figure 20 and Figure 21the waveform is captured at 264 VAC. The peak drain voltage, 496 V, is obtained at 264 Vload with two LEDs (see Figure 21). Under the same condition, the peak drain current is384 mA.Figure 18. Vds and Id at 176 VAC, one LEDFigure 19. Vds and Id at 176 VAC, two LEDs !- V !- V Top trace: Vin (200 V/div)Top trace: Vin (200 V/div)Bottom trace: Iin (200 mA/div)Bottom trace: Iin (200 mA/div)Time: 4 us/divTime: 4 us/divFigure 20. Vds and Id at 264 VAC, one LEDFigure 21. Vds and Id at 264 VAC, two LEDs !- V !- V Top trace: Vds (200 V/div)Top trace: Vin (200 V/div)Bottom trace: Id (200 mA/div)Bottom trace: Iin (200 mA/div)Time: 4 us/divTime: 4 us/div16/25Doc ID 14904 Rev 1
AN2811Test results and waveformsThe current sense circuit (R9 and R
stage directly. Compared to a buck converter, the flyback converter may be the better choice. Figure 4 shows the typical circuit of a flyback converter. Figure 4. Flyback converter The auxiliary winding can be added to the transformer (T1) to provide bias for Q1. Unlike the buck converter, T1 provides isolation between Vin and Vout.
AD210 PIN DESIGNATIONS Pin Designation Function 1 V O Output 2O COM Output Common 3 V OSS Isolated Power @ Output 4–V OSS –Isolated Power @ Output 14 V ISS Isolated Power @ Input 15 –V ISS –Isolated Power @ Input 16 FB Input Feedback 17 –IN –Input 18
The SN6501 is a monolithic oscillator/power-driver,specifically designed for small form factor, isolated power supplies in isolated interface applications. It drives a low-profile,center-tappedtransformer primary from a 3.3 V or 5 V DC power supply. The secondary can be wound to provide any isolated voltage based on transformer turns ratio.
The MAX253 monolithic oscillator/power-driver is specifically designed to provide isolated power for an isolated RS-485 or RS-232 data interface. The device drives a center-tapped transformer primary from a 5V or 3.3V DC power supply. The secondary can be wound to provide any isolated voltage needed at power levels up to 1W.
The SN6501 is a monolithic oscillator/power-driver,specifically designed for small form factor, isolated power supplies in isolated interface applications. It drives a low-profile,center-tappedtransformer primary from a 3.3 V or 5 V DC power supply. The secondary can be wound to provide any isolated voltage based on transformer turns ratio.
Head injuries were binned into six categories by ICD-9-CM code: isolated cerebral laceration or contusion (851.0 – 851.9), isolated subarachnoid hemorrhage (852.0 –852.1), isolated subdural hemorrhage (852.2-852.3), isolated epi-dural hematoma (852.4–852.5), and unspecified (853–
not connected to WEP's High Speed Wide Area Network (small pump stations, etc.) a . AB 1756 ControlLogix System employing the following modules and . Minimum Spares: 4 analog isolated outputs, 4 analog isolated inputs, 16 digital isolated outputs, 16 isolated digital inputs : Cimplicity.
CONS were isolated in 23 (10.6%) cases. CONS are frequently isolated from blood cultures and are emerging as important nosocomial pathogen. Most of the patients (95.7%) in whom CONS were isolated were of paediatric age group. CONS was isolated in 4.5% of cases in study by Gohel et al., (2014) and among 4% cases by van der Heijden et al. (2011).
Fungal strains were isolated from soil of sugarcane field Coimbatore, India by serial dilution plate method (Waksman, 1922). Fungus were isolated from 10-3 - 10 4 dilutions by plating into Potato Dextrose Agar (PDA) medium. Isolated fungal cultures were screened for protease enzyme production. The organisms were
