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TPS92210EVM-613 dimming question

Knighty
Intellectual 380 points
Other Parts Discussed in Thread: LMV321

Hi All,

we test TPS92210EVM with standart triac diming, the result as below

 - Use dimmer switch small model ( Panasonic 320W ) => Dimmable 0% to 100% , but blinking at about 30%.
 - Use dimmer switch big model ( Panasonic 540W ) => current drop to 140mA.

My concern is why the out put current drop to 140mA?

Thanks,

NT

  • 0
    TI__Genius 15910 points

    Dimmers vary in their internal filters and some can produce oscillations when interfacing with the input filter of the EVM.  If the triac current falls below the minimum holding current of the triac during this oscillation, the triac will be blocked until the next pulse.  Because the continuous conduction is prevented, the result is flickering.  Unfortunately the variation of dimmers makes it difficult to optimize an evaluation board to suit every design2781.dimmer inputs.doc. 

    I wasn't able to recreate the reduced LED current with the dimmers that I have here when set at maximum output.  Admittedly I do not have any Panasonic dimmers to test.  Every dimmer had some amount of blocking even when on full (see enclosed image).  But in every case I had to adjust the dimmer in order to record an LED current of 140mA.  Some dimmers had to be adjusted down to supply an input of 130Vrms and others down to 160Vrms in order to reduce the LED current.  Please check the  voltage waveform into the EVM to determine if the dimmer is blocking a significant portion of the input voltage. 

    Was the EVM regulating approximately 350mA with the dimmer out of the circuit?  If the output current is lower than the 350mA +/-20mA, I recommend changing R41 from 200k to 20k in order to reduce the effects of the input offset current of the LMV321 comparator.  You should also change C22 to 0.33uF in order to adjust the compensation for the new resistor value.  8032.dimmer inputs.doc

  • 0 in reply to Lisa Dinwoodie
    Prodigy 30 points

    Output Current without dimmer is 370mA here but with insertion of TRIAC dimmer flickering is introduced at lower currents. So can you recommend any specific dimmer of good enough quality and deign that is easily commercially available ?

    Thanks in Advance.