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TPS92075: Dimmer of TPS92075

giovanni copler
Prodigy 185 points
Part Number: TPS92075
Other Parts Discussed in Thread: TPS92210, UCC28811, LM3444

Dear Texas,

our cutomer ha requested an application in which we need to change on the fly the power of a led string. Is there any way to change from a microprocessor (not isolated) to output power of the leds using TPS92075?

The only way is by adding a triac or is there any other simpler way? I don't want top use a triac before it. Or should I use other IC? The requested power at full power is 25W.

Thanks,

Cristian

  • 0
    TI__Mastermind 18890 points

    Hi Cristian,

    Please give us a couple of days for this answer.

    Thanks Tuan

  • 0
    TI__Mastermind 28655 points

    Hello Cristian,

    What range of output power are you considering?  Is this a fixed LED stack voltage?  What is the stack voltage and maximum LED current?  Does you design need power factor correction?  Isolation is not a requirement?

    Best Regards,

  • 0 in reply to Irwin Nederbragt
    Prodigy 185 points

    Dear Irwin,

    it will be used in 4 different board, 2 with a power of 25W and other 2 with 11W. The leds number are fixed and each led need 2.8V. The 2 board with 11W are made of 100 led and 115 led, the other 2 of 25W are made of 225 led and 256 led. The 100 led are made of 10 strings in parallel of 10 led (28V), the 112 led are made of 8 parallel of 14 led (40V), the 225 are made of 15 parallel of 15 led (42V), the 256 are made of a parallel of 16 string of 16 led (45V).

    If needed i can change the number of parallel and series. What I can't change is the total number of led. 

    Our customer want a power from 0% to 100%. When the customer set 0% probably we will fixed the lowest possible current since he want to avoid a sharp step. We need the PFC.

    The driving will be through DALI (isolated), but there will be a microprocessor with the required optoisolators for isolation. The microprocessor have a PWM or DAC to drive the TPS92075. The microprocessor isn't isolated from the TPS92075

    Thanks,

  • 0 in reply to giovanni copler
    TI__Mastermind 28655 points

    Hello Cristian,

    From your information I get four operating points, 10P/10S at 11W Vled = 28V is 393 mA, 8P/14S at 11W Vled = 39.2V is 281 mA, 15P/15S at 25W Vled = 42V is 595 mA, 16P/16S at 25W Vled = 44.8V is 558 mA.

    If you can use a valley fill for the power factor correction the LM3444 might be a simple choice by driving the FILTER pin with a DC level if it is accurate enough for your application.  The valley fill may not be able to maintain better than 0.9 for all of your operating ranges if that is a concern.  The LM3444 regulates peak current so it will not dim linear though it can be mapped close with the micro setting the FILTER pin voltage.  If it needs linear dimming the LED current will need to be run through an error amplifier that a reference voltage can be set to to set current.  Some parts such as the TPS92210, UCC28811 could be set up to work like this.  There are some examples of isolated/flyback designs showing the current regulating circuit for these parts.

    Are you set on a buck converter and single stage solution?  For dimming two stage solutions tend to work much better.  A voltage generating stage running a buck converter.

    Best Regards,