polarity protection mosfet selection

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MrDEB

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am looking to add some polarity protection to my Mexican Train project but getting correct component? Having very little experience with mosfets I am using this as example
http://digital-diy.com/general-elec...ser-look-at-the-p-channel-mosfet-circuit.html
then using this as component

http://www.jameco.com/Jameco/Products/ProdDS/889760.pdf



this is a simple 4.5volt (3 AA batteries) powered circuit. Searched for a smaller inexpensive battery to use but the 3 AA holder is best I found but it is really to tall but it works.
 
That MOSFET should work fine.

If you want a smaller battery package you could use three AAA's.
If course you'd have to replace the batteries more often.
 
Battery life hopefully will no be an issue
ten 10K pull up resistors = .0045ma
10 leds w/330 ohm resistors aprox =13ma if all ten are on which is pretty rare.
AA batteries = 2000mah 1 game lasts 4 hours. on average only 3-4 leds are on.
On my revised board I have the mosfet and utilizing the HLVD feature.
On my proto type build I measure no more than 25ma w/ all the leds on but have three different colored leds.
 
MrDEB said:
the data sheet says vgs = -.4 min -.6 typ. -1.5 max
how to determine if this component will work?? as per this example
http://digital-diy.com/general-elec...ser-look-at-the-p-channel-mosfet-circuit.html
Click to expand...
For using a MOSFET as a switch it's not Vgs(th) that's critical it's the Vgs for a given ON resistance.
The data sheet for the P-MOSFET you selected shows the ON resistance as:

You can see that the ON resistance is quite small for a Vgs as low as -1.8V, so it will be fine with the 4.5V of 3 AA batteries.
 
Wouldn't a regular diode work better? Just a hobbyist but never heard of a mosfet for polarity protection.
 
Read the link MrDEB posted twice, by yours truly. It explains the advantages, namely, very little voltage drop compared to a diode, even a Shotkey.
 
Didn't read the link, thought it was just for a certain mosfet. Never saw one used like that before. Thanks
 
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