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IC for Traffic Light Led Driver

Nikos Chatzis
Prodigy 120 points
Other Parts Discussed in Thread: LM3447, TPS92410

Hello to forum!!

           

            We are a company based in Thessaloniki Greece, which focuses its activities in the sector of traffic control. Our R&D department is in the design process of a power supply device that will be used to drive the LED disks (red, amber and green) in a traffic light device. Having worked in the past with various products of your company and being fully satisfied, we would like you to suggest some of your available devices (SMPS, regulators, converters, etc) in order to help us complete this project.

            Some of the desirable features of our device that will help you select the IC you consider suitable for our case will be described below:

 

• Input: The operating voltage of the power supply is 230VAC and comes from an external controller. It can supply our device with three voltage levels which will determine how the device will work. More specifically, for voltages <90 VAC the power supply will be in the off-state. For voltages 90VAC <Vin <170VAC, output should be in a the low-state (70% of normal operation). Finally, for voltages 170VAC <Vin <230VAC power supply will operate normally.

• Output: Each power supply device will drive one of the aforementioned Led discs with constant current. Each disc consists of 10 strings connected in parallel and in each string there are 12 Leds connected in series. The output voltage ranges from 23 to 26 VDC. At this point there are three main issues:

1. Output current should remain constant for each LED string even if one or more strings go out of order so that the remaining leds don’t overburden. (Self-Adjusting Current Sharing Mode)

2. If a certain number of leds (e.g. 40%) fail, the power supply should sense the change in the output voltage and enter into off-state.

3. Because the operating voltage of led discs differs from color to color (red, amber, green) the power supply will be able to provide the appropriate current for each disc either automatically (which is the most desired) or by using a DIP switch.

 

            Having studied the respective design guides of your company we have identified some ICs that could meet the requirements of our device, but we also want you to suggest us- based on the above characteristics – which one of your available solutions you consider the more efficient for our project.

 

Don’t hesitate to ask for further information.

Thank you in advance!

 

Chatzis Nikolaos

Electronics/Embedded Engineer

R&D Dep. Simatodotisi

Thessaloniki, Greece

  • 0
    TI__Intellectual 2540 points

    Chatzis,

    There are several potential ways to realize this type of design.  Below is one possibility using direct AC/DC LED drive for each color disc.  Other possibilities would be AC/DC with constant voltage outputs and current regulators for each disc.  There are merits and demerits of each approach, of course.

    You mentioned that you have identified some TI products which could be suitable.  Which are you looking at as it might help us to narrow to possibilities?

     

    B/R

    John

  • 0 in reply to John Perry
    Prodigy 120 points
    Dear John,
    First of all I would like to thank you for spending your time over my project, and also for your useful designs.

    So let me explain you the basic idea of my project...

    At first, I chose the LM3447 IC as a SMPS controller because of its great output current protection features and its dimming possibilities.
    But...that dimming technique is working only with triacs.

    As you can read at my mail above, where the input dot is, my system has to have 3 AC input levels coming from an external controller. So at this point I'm looking for a device that can measure the input voltage (rms to dc converter???) and will produce respective output voltage. This output must drive the dimming pin of a SMPS controller like TPS92410. Thus, i suppose that I could control the output current accordingly to the input voltage.

    What i want from you is to inform me whether this topology is possible or not. Also i want to know if there is a similar device to LM3447 but with anolog/linear dimming.

    If we can handle these problems we can discuss later for the output features.

    Thank you again for your time!!!

    Best regards

    Nick