[vdr] Re: cool down of dvb 1.3

["Reinhard Walter Buchner" <rw.buchner@freenet.de>]

Hi Johannes,

> i know this has been discussed before (heat "problem" of 1.3)
> but another idea: would i help to feed the lnb with an external power
> supply? so the dvbs doesn't need to provide the power?

I don't think this would help, because the tuner *doesn't* supply
LNB power ;o)) There are two chips on the DVB, which provide
LNB power. One is a bucking step-up converter (28V) and the
other is the LNBP chip, which finally supplies the LNB with
power. Both of these chips can easily handle the LNB power
needs (max 500mA as per specs). The boost convertor can
handle 3A cont (6A peak) and the LNBP can sink 900mA
continious duty.

The problem simply is a design flaw (imo) in the tuner itself
(and not the surrounding circuitry). So unloading the LNB
power circuit *may* help the card run a little cooler, but it
will do nothing in terms of cutting down the heat that the
actual tuner chip (where the metal tongue of the shield
rests on) produces.

Greetz,
Reinhard


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