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TPS92210: About the supporting of TRIAC dimmer

Part Number: TPS92210
Other Parts Discussed in Thread: LM3445, LM3450, LM3447, TPS92002, TPS92001



Regarding to the TRIAC dimmer type on TPS92210 , my customer is asking some question.


(1) What type of dimmer will be supported on this device?

(leading edge or trailing edge?)

(2) About other LED drivers(TRIAC dimmer supported, what type of dimmer will be supported on following device?





(3) Is there any LED driver that support trailing edge dimmer or both types of dimmer?




  • Thanks for your response. As far as the TPS92210, we support both leading and trailing edge dimmers. Dimmer compatibility is achieved in the secondary by external circuits and hence depending on the customer list of dimmers, the performance can be adjusted. I will add other experts to weigh in on the other products.

  • Hello,

    TPS92210 was answered.

    LM3445, LM3450, LM3447 will support both leading and trailing edge dimmers.  Performance would be based on how the circuit using these parts was designed.  A lot of parts can be made to be compatible with both with significant added circuitry, these parts were designed for both.  Leading edge and trailing edge have two different concerns when designing for compatibility with them


  • Hello Irwin,


    Thank you for reply.

    I have informed information from you to my customer.

    I have some additional question.

    (4) I understand that we need to refer EVM schematics to support leading/trailing edge.

    When they need to tune for dimmer, what point of schematics do they need to modify?

    Do you have some information(document) for tuning for dimmer?

    (5) You mentioned that leading edge and trailing edge have two different concerns when designing for compatibility with them.

    Could you please explain me more detail about two different concerns?

    (6)It seems that LM3447 is simple schematics and I think that it will be best to support both type dimmer.

    If their specification is matched, they might use this device.

    Could you please give me comment or advice?




  • Hello,

    4)  Best thing would be to get an EVM and try it.  We have set up the EVMs to work with most dimmers.  If it is adequate as the standard EVM they can base their design on that.  Things may change depending on the power level and input operating voltage.

    5)  Leading edge dimmers, or triac dimmers, need a certain amount of holding current to keep the triac on.  There are two main things to be concerned with on a design using LEDs.  The first is preventing the input current from ringing negative from the leading edge transient.  Triac dimmers want to see a resistive load, and LED driver with an EMI filter will look partially capacitive causing the input current to want to ring.  An RC damper can be used to keep the current from ringing negative (it will be on the EVM schematic).  the second issue is to make sure there is enough holding current during the AC falling waveform.  Since the power is generally lower and there are capacitors trying to hold up the rectified rail there can be issues related to having enough hold current for the triac.  This will cause it to turn off prematurely which can cause flicker and undesired operation.  This is more difficult to deal with on 230/240 VAC designs.

    6)  The LM3447 is a good choice to look at, it was developed after the LM3445 and LM3450.