H
Henrik [7182]
- Jan 1, 1970
- 0
Hello experts
Still rather new to the world of SEPIC, I have a problem with a design.
I have made a circuit based on the datasheet for the LM3478. It is intended
to run with Vin from 10V to 32V and deliver 24V out with a maximum of 4Amps.
My testsetup runs at 32V input. The circuit is as can be seen here:
www.impc.dk/scm/lm3478sepic.pdf
A colleague of mine recently built something quite similar but with the
LTC1871 controller instead. But I'd rather use the national part, since we
already has this part in stock.
When I run with no load, output is 24V and everything is nice. But when I
load the darn thing, even only by one amp, everything gets so hot and
eventually the sense resistors crack.
I plan to change R79 so that I run at 200kHz, because according to my
calculations 100kHz is a little to slow for my 22uH/13A inductors.
This heat issue has me puzzled somewhat but before i dive into measuring, I
wonder if anyone would have a comment on the schematic. Especially regarding
the values for R103/C16 and R145 which I have been struggling to
determine.But also if I need anything or need to change anything. Not much
is to be found on google regarding SEPIC with this chip, unfortunately.
I am eager to learn, but still a beginner in this field, so be gentle ;-)
Thanking you in advance for any and all help.
Best regards
Henrik
Still rather new to the world of SEPIC, I have a problem with a design.
I have made a circuit based on the datasheet for the LM3478. It is intended
to run with Vin from 10V to 32V and deliver 24V out with a maximum of 4Amps.
My testsetup runs at 32V input. The circuit is as can be seen here:
www.impc.dk/scm/lm3478sepic.pdf
A colleague of mine recently built something quite similar but with the
LTC1871 controller instead. But I'd rather use the national part, since we
already has this part in stock.
When I run with no load, output is 24V and everything is nice. But when I
load the darn thing, even only by one amp, everything gets so hot and
eventually the sense resistors crack.
I plan to change R79 so that I run at 200kHz, because according to my
calculations 100kHz is a little to slow for my 22uH/13A inductors.
This heat issue has me puzzled somewhat but before i dive into measuring, I
wonder if anyone would have a comment on the schematic. Especially regarding
the values for R103/C16 and R145 which I have been struggling to
determine.But also if I need anything or need to change anything. Not much
is to be found on google regarding SEPIC with this chip, unfortunately.
I am eager to learn, but still a beginner in this field, so be gentle ;-)
Thanking you in advance for any and all help.
Best regards
Henrik