Low drop diode

MOSFET as diode???

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Low drop diode

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Gepostet: 30.10.2010 - 09:47 Uhr  ·  #1
Hello,

I am losing my time on a field, that I do not know – MOSFET. Namely, in a design, I have two possible sources of voltage – it can be active any of them or both with max 150mA. Till now I was on 5V and to have two diodes BAT754 it was not so big drop in percentage.

Now I switched to 3,3V and every mV counts. On net I saw design with MOSFET as a low drop diode. Since I need two, I tried with IRF7754 with around 34mOhm ON resistance. Result? If I apply voltage on any of inputs, there is a short. :devil:

Do any have any idea where I made mistake or how to solve this other way? Tnx.

Best regards,
Andrej
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Re: Low drop diode

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Gepostet: 31.10.2010 - 09:39 Uhr  ·  #2
Hi,

found the reason - not in wrong usage of MOSFET. There was 3,3V zener which was solded in wrong direction. :'(

Now, there is no short on power lines but MOSFETS are not working as diode - if I apply power to one input, I have it also on other. :(

Looks like, I will switch to more expensive solution an add two LTC4411 - increasing component count but it should work. 8-)
Andrej
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