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LM3445 design request

Srinivasan Velmurugan
Prodigy 40 points
Other Parts Discussed in Thread: LM3445

  1. I was working on the circuit in 'AN-1995 LM3445 208-277VAC Non-Isolated Evaluation PCB'. While working with this, the components Q2,Q7 and LM3445 were burnt. I used the exact components mentioned in the BOM' but I couldn't find out the reason behind this. Kindly help me to know why it burnt even working as per the document. (refer the attachment - schematic).
  2. My requirement is to work with AC Input (90 VAC to 260 VAC) to drive multiple LED's in series(8 LED's) up to 350mA average current. To achieve my requirement with the same design 'AN-1995', what modification has to be done in the circuit/what extra components are needed.

I analysed the reason as per the design calculation steps of 'AN-1995' document. Kindly suggest whether my below calculations are correct for further
proceeding.

VBUCK Min = 45
VBUCK Max = 382

toff = 1-1/0.8 * 22.4/214 sqrt(2) / 250KHz
toff = 3.629 micro seconds

ton = 3.58 micro seconds

R4 = 320 K

C11 = 199 pF

L2 = 635 Micro Henry

C10 = 1 Micro F 200V

C7 = C9 = 22 Micro Farrad

Kindly help me to sort out above issues. Thanks in advance.

  • 0
    TI__Expert 3495 points
    Sirinivasan: 1. It is hard for Q7 to get burned. Was that burned component Q9?
    2. We don't publish universal input LED light bulb reference designs becasuse those reference designs are not very useful. After realizing the extra cost of doing universal input LED light bulb, all the customers switched to 120Vac or 230Vac designs.
    David Zhang