schematics:
http://www.flickr.com/photos/30099443@N05/2819532574/sizes/l/
this LED current driver comes from LM3433 by NSC. I am new to the
power electronics. I made a same circuits as this evaluation board
(NSC application notes AN-1736), my circuits failed after 20 mins
without any signs. I used a hot air gun (~700 F) to solder this QFN
and I wonder I damaged this part. Is it possible?
1. The Mosfet got hot but the waveform was clean, the edge is ~100 ns
and it must be fully-on or off. Why it failed without any sign? The
waveform at Q1 and Q2 "S" likes this:
_________ __ ___________ this is not a single toggle up and down
switching signal?
|_| |_|
2.How does the current flow in sync. mosfets? It looks the load is
different from conventional sync. buck converter.
3. Why the designer put so many bead and capacitors in parallel? to
minimize the ESR and suppress the ringing from switching?
4. D3 is to protect the LED from the reversed voltage from the main
inductor?
http://www.flickr.com/photos/30099443@N05/2819532574/sizes/l/
this LED current driver comes from LM3433 by NSC. I am new to the
power electronics. I made a same circuits as this evaluation board
(NSC application notes AN-1736), my circuits failed after 20 mins
without any signs. I used a hot air gun (~700 F) to solder this QFN
and I wonder I damaged this part. Is it possible?
1. The Mosfet got hot but the waveform was clean, the edge is ~100 ns
and it must be fully-on or off. Why it failed without any sign? The
waveform at Q1 and Q2 "S" likes this:
_________ __ ___________ this is not a single toggle up and down
switching signal?
|_| |_|
2.How does the current flow in sync. mosfets? It looks the load is
different from conventional sync. buck converter.
3. Why the designer put so many bead and capacitors in parallel? to
minimize the ESR and suppress the ringing from switching?
4. D3 is to protect the LED from the reversed voltage from the main
inductor?
