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LM3445: Start-up time

tateo yamashiro
Guru 10890 points
Part Number: LM3445

Hi,

We got a question from the customer about LM3445.
Could you help us?

[Question]
How can we estimate the start-up time under the following condition?

 Topology: Isolated Flybuck
 Dimming: Triac dimming
 Vin: AC90~110V
 Vf: 30~42V
 Iled: 3mA (1% of max 300mA); conduction angle is 35 degree

Their requirement of start-up time is less than 1sec. Are there any ICs to meet their requirement?

Best Regards,
tateo

  • 0
    TI__Mastermind 28655 points
    Hello Tateo,

    The start up time will be dominated by the output capacitor charging. If this is off-line I assume it will be Power Factor Corrected and will not have 100% ripple. If this is the case the output capacitor will be large. The calculation will be I = C*(dv/dt), where I is 3 mA, dv is the LED Vf C is the output capacitor, t will be the charge time. Also, it is difficult to design a triac dimming circuit that will start at 1% dim level.

    Best Regards,