LM2587 12V to 48V Boost Regulator Design - Help Needed

DavidM

HI,

I have a previous design of mine for a 12V to +48V( approx) boost Regulator circuit using the LM2587T-ADJ regulator from Nat Semi, that was throughhole design ( with a big heat sink) , and Now I need to convert to SMD and keep the costs down as well as the overall pcb area using the LM2587S-ADJ SMD part.
My design will run from a 12V SLA 2.2AH Battery. I need to produce ( On Call ) about 1 to 2 amps for less than 1 second from time to time. ( i.e very low duty)

I have attached the Schematic & PCB Layout ( my current design), I have been reading through the DATA SHEET for the LM2587 from National Semi, and some things are not described to well.

Q1) OUTPUT CAPACITORS ( C2, C3), The caps I have chosen, each have an ac ripple current of 1410mA each , So do I get 2820mA? I do believe I get a doubling of the capacitance ( i.e 940uf). And I have read the they must be "matched" parts as far as the ESR and Ripple is concerned. So Does two of the same caps in parallel provide an increase ( doubling ) of Ripple Current Rating?

Q2) Is there some kind of SMD Heat sink which I can use? (I have a dotted outline showing where I would like one to go) With heat sinks being made of Aluminium, how does one attach/solder such a device? Is this possible, Other Options?

Q3) The DIode ( MURS320) I have chosen "I believe" is similar to an MBR20100CT through hole part, would this be true?, The MURS320 is rated at 3 amps, 200v , The MBR20100CT was rated at 10Amps 100V. Do I need a lot of Amps?

Q4) My Current T/H Design has used both a 100UH, or 120UH Inductor, (both rated at 3 to 2.5amps) The SMD Inductor I have chosen (Bourns SRR1210-101M) is 100UH 3 Amps, but is a much smaller footprint than the T/H Part and its shielded, If I want to go for higher amps, I need to go lower in Inductance, But I am not sure what the inductance "value" does in this design, there is some crazy formula in the data sheet, but I cannot understand it.



Thanks ( Sorry about all the questions)

Dave M

Peter KG6LSE

Q2) Is there some kind of SMD Heat sink which I can use? (I have a dotted outline showing where I would like one to go) With heat sinks being made of Aluminium, how does one attach/solder such a device? Is this possible, Other Options?


Copper ! its easy to find . use a chunk of pipe . hammer flat and now you have a Fin you can attach and bend .

DavidM

Peter KG6LSE wrote: »

its easy to find . use a chunk of pipe . hammer flat and now you have a Fin you can attach and bend .

HI Peter, I think I need something a bit more professional that that, but a cute idea!

I just found this device..

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=DV-T263-101E-ND

I am manufacturing these on SMD Machine pick & place.

Dave M

DavidM

OK,

Heatsink issue solved, I shall use the D-Sink Device.


Can any please comment on the capacitors?


Thanks

DavidM

I really do need help with the capacitors! (i.e Ripple current Question)

I was thinking of using 3 X 470UF 6v for all the capacitors, That would bring down the cost of the build, What do you think?

Thanks

Dave M

sam_sam_sam

I was thinking of using 3 X 470UF 6v for all the capacitors,

The only thing that can tell you that voltage rating on the capacitors need to be higher than the working voltage of that part of the circuit

DavidM

Hi Sam,

That was a typo, It should be 63V of course!

Thanks

Dave M