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LED Street Lighting Power supply

Jason

Hello All,

As we know, LED is used moreand more on street lighting, in the future, LED will replace the traditional street lighting bulb. Many supplier have there own power supply solution for LED street lighting, such as NXP, ON, PI,TI, Fairchild and so on, some solution is isolated Fly-back and some is non-isolated high voltage Buck to drive LED bulb, some solution use PFC controller and some use Valley PFC circuit to increase power factor. The question is which solution is more popular for the LED street lighting? isolated or non-isolated,  PFC controller or Valley PFC circuit?

  • in reply to Jorge_Garcia
    Isolated drivers are typically implemented because they simplify and improve the LED module/array connection to the heatsink. Typically Street lights have a good amount of external surface that can help the heatsinking strategy so isolating it the LED driver from the LEDs allows one to take better advantage of thermally connecting the LED array to the external surface. Also, typically street light certification requires some level ingress protection (IPxx) and general UL safety. Isolating the LED array from the AC input helps with that requirement as well.
    Active PFC control is better because it is more efficient that Valley fill PFC. Valley Fill PFC is ok low power lighting applications – like residential - but the extra dissipation usually does not make it favorable to higher power applications like street lighting.
     
    TI has soem veru cost effective Street lighting LED driver solutions that will cost effectively help with the requirements and issues mentioned in this discussion.
     
     
    I hope this helps.
  • in reply to Former Member

    Hi Guys,

     

    A lot is being said about topology choices and implementations. Enough to build something worthwile. Anyway, i like to share some interesting; the near future of power control.

     

    AN1271 : Isolated Flyback converter to drive LEDS with active PFC function.

     

    http://ww1.microchip.com/downloads/en/AppNotes/01271A.pdf

     

    The scheme is not fully digital control as the microcontroller has analog peripherals for the control loop. This is a very nice way to make the next step. I have samples on my desk of this controller, now i have to find the time to play with the device.

     

    Best regards, Enrico Migchels

  • in reply to enrico.migchels

    Hi Enrico,

     

    Great document! I think i am trying to build that circuit int the next days to see how it works. And i would be glad to hear about your experiments though.

     

    Thanks for your sharing.

     

    Firat

  • in reply to Jorge_Garcia

    Hi Jorge,

    I will set three type of output current beforehand which is 350mA, 700mA, 1050mA, that means my full load is about 36W and my light load is only 12W. The power factor become the big problem when light load and high voltage input.

  • in reply to Former Member

    Hi Peter,

    Lighting certification and safety requirement is the main reason to design a Isolated driver, but the cost also take into account, maybe the Single-Stage Flyback is the best choice. What you say?

     

    Jason

  • in reply to enrico.migchels

    Hi Enrico,

    The solution is wonderful, it is a singel stage topology but the controller is a MCU not the PFC controller. there is only primary detection, no secondary feedback. Use MCU can make the duty cycle accurately. But I have some questions:

    1,How to protect the driver when the secondary occur Over Voltage, Over Current, or Over Load?

    2,How to burn the code into the MCU, when the AC power is connect or not? If AC power is connect, how to isolated the ICSP Header and the AC input? If not, how to power the MCU?

     

     

    Jason

  • in reply to firatkocak

    Hi Firat,

    What about you try,does it work well? I,m glad to hear about your experiment.

    Jason

     

     

  • in reply to Jason

    Hi Jason,

     

    I hope you are doing well. I know this questions is for Enrico and I'm sure he'll chime in with his suggestions, but I'd like to take a crack at answering your questions.

     

    1.  I think Over voltage, Over Current, and Over load should be defined first. An over load will generally be caused by an over voltage fault or an overcurrent fault so you don't have to think about the over load as a seperate fault condition, if you take care of overvoltage and overcurrent conditions than the over load condition is also taken care of.

     

    Since your going to regulate current in the LEDs a short circuit condition will not be so bad. The flyback control loop will adjust the duty cycle in order to maintain a constant current, however you don't want the supply to stay in this condition for too long so once the condition is detected (say through a voltage divider across the output) then the MCU should shutdown the converter.

     

    An open circuit condition is far more serious because the control loop is trying to regulate current in an open circuit current can't flow to the sensing element (resistor, current transformer, etc.) so the control loop will continually increase the duty cycle to try to increase the current over time the the stress on the transistor and diode will become excessive and these components will be destroyed. The best way to handle this situation is to have a switchable load on the output ( the simplest example is a power resistor which is switch in on the low side with an NPN BJT or N channel FET) Once the open circuit condition is sensed then the MCU can activate the load across the output at which point current flow and the circuit can maintain regulation.

     

    2. Due to the low voltages and current needed by the MCU you'll generally have to make a secondary low power housekeeping supply and their are many ways to go about this. A few examples would be a bootstrap circuit , Auto oscillating buck converter, Royer converter, even a low power flyback would be suitable as a housekeeping supply.

     

    Most MCUs save program data in non-volatile EEPROM memory so you don't have to worry about losing your code once the power is removed.

     

    I hope this helps if you have any other questions please feel free to contact us.

     

    Best Regards,

     

    Jorge Garcia

    Cadsoft Computer

  • in reply to Jorge_Garcia

    Thanks Jorge,

    It's very exciting that you replied.

     

    I do not know well how dose the MCU work.If I use a PFC controller for Single-stage Flyback application, I well set my OPP in primary, OVP and OCP in secondary. Generally,OPP is caused by an over voltage fault or an overcurrent fault,  the circuit will continued work untill some components are broken. It is necessary to setting OPP in primary to prevent broken the circuit .

     

    An open loop control is much difficult than closed-loop control. For open loop control, the contoller (no matter MCU or PFC IC) didn't know the situation of the output. But for closed-loop control, feedback signal will be detect by the controller.

     

    By the way, use MCU as the contoller is much expensive and complex than use PFC controller, and MCU is difficult to me, I don't know how to write the code, how to burn the code into the MCU. Use MCU, that means 'mission impossibility' image

     

    So, use PFC controller to finish this project is my decision. I find Fairchild's FAN7530 is suitable to my project.

     

    You can see my schematic circuit based on FAN7530 as follow.

     

    image

  • in reply to Jason

    Hi Jason,

     

    I hope you are doing well.

     

    Don't worry you're not obligated to use an MCU.image

     

    You're on the right track, the only problem is that as it stands you have only made a Flyback converter, the chip itself is designed for Critical Conductin mode PFC not to run a Flyback.

     

    However from the brief look at the schematic you've given it seems like your trying to adapt it. If you've done this before than go with it, I'm just a little cautious because the chip isn't designed to run a Flyback but rather a boost PFC and I generally try to stick to manufacturer recommendations.

     

    In one of my earlier post I mentioned TI's LED cookbook which already contains some reference solutions to the driver your trying to create, so I hope you can take a little time to look it through, I think it will be well worth your time.

     

    hth,

     

    Jorge Garcia

    Cadsoft Computer