[aprssig] Increased Diode Efficiency

[AC]

On 7/5/2013 10:00, aprssig-request at tapr.org wrote:

> Message: 1
> Date: Fri, 5 Jul 2013 09:47:00 -0400
> From: Robert Bruninga <bruninga at usna.edu>
> To: aprssig at tapr.org
> Subject: [aprssig] Increased Diode Efficiency
> Message-ID: <cd3c9376fe95a100e114e333c75a8bbd at mail.gmail.com>
> Content-Type: text/plain; charset=ISO-8859-1
>
> For anyone ever frustrated by the 0.7 to 1V voltage drop across rectifiers
> in low voltage circuits, there is now a chip that can drive nearly-zero
> resistance MOSfets to do the rectification with nearly zero voltage loss
> (and hence, no need for heatsinks):
>
> Linear Technology has released a new IC making possible to achieve a
> perfect bridge rectifier :
>
> http://cds.linear.com/docs/en/press-release/LT4320.pdf
> http://video.linear.com/136 <http://video.linear.com/136>
>
> I donno whether they can work as distribution diodes too, (isolation
> diodes for batteries etc,) but it looks promising for higher power 12v
> stuff.
>
> Bob, WB4APR

 From the data sheet it is designed exactly as described, to replace a 
four-diode bridge rectifier and not a single diode.  So no, you can't 
use this chip to replace the Schottky diodes that are used for things 
like the PowerGate battery isolator.

If you want to use active switching for battery isolators, you need the 
LTC4355 chip which performs the same task using MOSFETs instead of 
Schottky diodes.  This chip also can monitor for power faults (too much 
power across the MOSFETs) and fuse faults (blown fuse).


Note for all:  Schottky diodes do not have 0.7V diode drops, they are 
usually between 0.15 and 0.45 volts which is why battery isolators and 
other high current applications use them.  Only standard P-N junction 
silicon diodes have 0.7V diode drops.  However, they do have higher 
leakage current (you can't get something for nothing) so very low diode 
drop versions (such as the 0.15) will leak quite a bit of current in the 
reverse bias direction.