[SOLVED] reverse battery protection NMOS Fet

[sheng]

What is a good rule of thumb for picking a NMOs fet for reverse battery protection for a ultra low voltage circuit? Vin Max is 5.5v or 6v. Right now, I am using a CRS06 Schottky in series with my 6v battery but its drain to much voltage in idle mow. Any suggestion NMOS Fet?

Thanks.

 

[KlausST]

Hi,

You tell us nothing about current...

I'd try a p channel fet. Gate to gnd, D to +Battery, S to + Application.

Klaus

 

[sheng]

Hi KlausSt,

My circuit is running at 250mA. From what I red, Nmos Fet is a better choose for my circuit but just don't know how to choose them for the lowest forward voltage drop. Thanks

 

[KlausST]

Hi,

Many logic level mostfets can handle 6V Vgs.
In SOT23 there are cheap ones with Rdson of less than 100mOhms. Giving 25mV voltage drop.


Klaus

 

[dimmich]

There are modern transistors with good parameters. For example such as:

AO3401 (P-channel, Rds 0.050 Ohm, Vds 30V, Id 4.0A, Vgs min 2.5V, SOT23)
IRLML6401 (P-channel, Rds 0.050 Ohm, Vds 12V, Id 4.3A, Vgs min 1.8V, SOT23)
IRLML2502 (N-channel, Rds 0.045 Ohm, Vds 20V, Id 4.2A, Vgs min 2.25V, SOT23)
SI2336DS (N-channel, Rds 0.042 Ohm, Vds 30V, Id 5.2A, Vgs min 1.8V, SOT23)
AP2306AGN (N-channel, Rds 0.035 Ohm, Vds 30V, Id 5.0A, Vgs min 1.8V, SOT23)

In you application convenient to use P-channel.

 

[sheng]

Thanks Klaus and Dimmich for the information.