Re: Low efficiency from SEPIC converter

From: Pooh Bear (rabbitsfriendsandrelations_at_hotmail.com)
Date: 08/16/04 

Date: Mon, 16 Aug 2004 21:02:39 +0100

Liam wrote:

> Hi
> My company has had a long standing design based on the LT1371 in a
> SEPIC configuration. Its worked fine in that application but we had a
> bit of shock when we found its efficiency is only 55%.
> Our new application requires as high a figure as possible.
>
> The circuit used is the one in the data ***. One possible problem is
> that our application normally draws 80mA ( 55 % efficient ) but
> occasionally requires a pulse of 0.5A.
>
> The components are as shown on the circuit except for the diode which
> is a MBRS340T3 and C2 which is an AVX TPS series ( could'nt get hold
> the specified one ).
>
> Does anyone have any idea where we've gone wrong. The linear tech
> switchercad software reckons we should get 85% efficiency.

I've had disappointing efficiency from an LT switcher device many yrs back
too.

I would suspect indifferent inductor performance as something worth
investigating initially.

Graham