LM3429: efficiency 80% and low on frequency more than 300khz

Signal on MOSTET's gate

Signal on Induction:

Hello Ivan,

The last scope capture that you have is where in the schematic?  I do not understand induction...Is this on the drain of the FET connecting to the inductor?  It looks like you are boosting the voltage to about 55V is that correct?

Thanks Tuan

Thanks, Tuan

1) last scope into connection mosfet's Q1 drain and inductor L1

2) Inductor's CDRH127/LDNP-680MC datasheet: products.sumida.com/.../CDRH127LD (en).pdf

3) Yes, drain connext to inductor

4) Yes, boost voltage is 55V

5) Schematic in other variant:

Hello Ivan,

I have an issue with the last scope capture that shows negative 38V.  There should not be any negative voltage on the board at all.  The FET Q1 when turn ON should show the voltage on the Drain to be close to 0V (small positive voltage).  There is something wrong here that does not make sense to me.

Thanks Tuan

Hello, Tuan

Sorry, I remeasure diagrams with the help of other equipment. Amplitude measure must be X10, because I use 10 devided probe

1) Point mosfet Q1 drain and Inductor (amplitude measure must be X10):

2) Point mosfet gate (amplitude measure must be X10):

3)Yellow - Point mosfet gate (amplitude measure must be X10)

Blue - Point gate and Inductor (amplitude measure must be X10):

4) Point LED + AC mode, filtered DC (amplitude measure must be X10):

5) Yellow - Point LED + AC mode, filtered DC (amplitude measure must be X10)

Blue - Point LED + AC mode, filtered DC (amplitude measure must be X10):

6) Yellow - Point LED + AC mode, filtered DC (amplitude measure must be X10)

Blue - Point gate and Inductor (amplitude measure must be X10):