purchasing Mosfets

[MrDEB]

Working on a simple battery protection (reverse) using a P chanel mosfet.
Using octopart to locate and most suppliers have no stock.
Even went to Ebay.
battery source is 6v
amperage draw under 1 amp (300-600ma)
still searching wanting to avoid outside the USA

 

[sagor1]

Purchase from a reputable distributor like Digikey, Mouser or Newark. At least you are likely to get the "real thing". Other sources generally all come from China, and some of those are re-labeled devices that never meet original specifications.
The reputable dealers allow you to search by parameters, so you can search for things like RDSon, voltage, current, etc. Also, in your case, if everything is powered by 6V, you will need "logic level" gate voltage specifications. Most MOSFETs require 10V to turn on fully. Logic level devices will be fully on at around the 5V (4.5V) gate voltage

 

[tumbleweed]

Using octopart to locate and most suppliers have no stock.

... of what part?

Do you really need 600mA??

 

[rjenkinsgb]

Mouser have literally hundreds of logic level P channel mosfets available.

This is a nice example:

https://eu.mouser.com/ProductDetail/Vishay-Siliconix/SI2301CDS-T1-BE3?qs=CiayqK2gdcJNFARNd%252BC6jg%3D%3D

Digikey have the same part in stock:

SI2301CDS-T1-E3 Vishay Siliconix | Discrete Semiconductor Products | DigiKey

Order today, ships today. SI2301CDS-T1-E3 – P-Channel 20 V 3.1A (Tc) 860mW (Ta), 1.6W (Tc) Surface Mount SOT-23-3 (TO-236) from Vishay Siliconix. Pricing and Availability on millions of electronic components from Digi-Key Electronics.

www.digikey.com

Or a higher power, lower on resistance one:

https://eu.mouser.com/ProductDetail/ROHM-Semiconductor/RD3G01BATTL1?qs=IS%252B4QmGtzzq4rSy9%2FX6zdw%3D%3D

 

[MrDEB]

should have stated a SMD and 600ma - 1 amp should be conservetive?

 

[rjenkinsgb]

should have stated a SMD and 600ma - 1 amp should be conservetive?

Those are both surface mount?

ON resistance is the critical value for a device being used as a power switch; it makes no difference if it's rated for higher current, as long as the on resistance is low enough to keep the voltage drop and power loss down to acceptable levels.

 

[tumbleweed]

Be sure to pick a part that has a Vgs (max) spec in the right range for your desired input voltage, or you will have to add additional components to protect it.

For example the SI2301 called out above has a Vgs spec of +/-8V.
That would be fine for your stated 6VIN, but if you ever used that part with a 9V or 12V input you would have to clamp Vgs so as not to exceed that 8V.

 

[MrDEB]

Thanks for all the input.
I have on my project manager at Mouser the Si2301 mosfet.
Made changes to three projects that currently using a diod for reverse battery protection.
It was suggested in another thread https://www.electro-tech-online.com/threads/mosfet-reverse-battery-protection.162737/post-1416225
that I really don't need the zenier diode? plan is the zenier and 100 ohm resistor?

 

[tumbleweed]

...I really don't need the zenier diode? plan is the zenier and 100 ohm resistor?

Did you ever watch the video on the hackaday page I linked to in post #12 of your other thread?
It explains everything.

To go back to that thread, you show a schematic with a STN3P6F6 P-chan 60V 3A sot-223 device, a 12V zener (not sure of the P/N), and a 100 ohm resistor.
The STN3P6F6 has a Vgs rating of +/-20V, so unless you plan on having a DC input > 20V you don't need the zener (and resistor) with that part. That's a hefty part, and would work for just about anything up to 15VIN, but it's probably overkill.

The Si2301 has a Vgs rating of +/-8V, so as long as you don't plan on using a DC input > 8V you don't need the zener (and resistor) with that part either.
If you DO want a larger input range then you'll want a zener (and resistor), but NOT a 12V one... maybe 5V-6V. Again, the video explains all this.

The Si2301 is in a different package type than your original schematic (SOT-23 vs a SOT-223), so watch out for that.
If/when you redo the schematic pay attention to which pins are which (D-S-G). Connect VIN to the Drain, Output to the Source, and "GND" to the Gate.
It is important to wire it "backwards" of how you would normally use it so that under normal operation the D-S body diode is forward-biased and conducts.

 

[MrDEB]

yes I watched the video, thanks very informative.
I redid the schematic and need to recheck if the pins are connected correctly.

 

[MrDEB]

Here is a redo of schematic using the LIBRARY LOADER for the correct pattern

 

[tumbleweed]

Remove the connection between the fet gate (G) and source (S)... you're shorting the output (S) to GND (G).

 

[MrDEB]

good point dumb me.

 

[Externet]

I pile up dozens if not hundreds of mosfets salvaged in management boards removed from bad lithium battery packs from tools and laptops. Perhaps can become a source for you too, $0 and in many flavors.

 

[MrDEB]

Well finally got my mosfets and soldered one on the board.
Now It won't program.
Thinking back to a discussion with Tumbleweed, I may need to connect a jumper from Vcc to the Drain on the mosfet.
or pull the mosfet off and see if I can program.
WAS working before I put the mosfet on the board.

 

[Nigel Goodwin]

Which FET did you solder in place?.

 

[MrDEB]

that would probally help.

SI2301CDS-T1-E3 Vishay Siliconix | Discrete Semiconductor Products | DigiKey

Order today, ships today. SI2301CDS-T1-E3 – P-Channel 20 V 3.1A (Tc) 860mW (Ta), 1.6W (Tc) Surface Mount SOT-23-3 (TO-236) from Vishay Siliconix. Pricing and Availability on millions of electronic components from Digi-Key Electronics.

www.digikey.com

I ordered from Newark and no sooner I ordered, the Mouser ordered was delivered.

 

[Nigel Goodwin]

No, which FET location on the board.

 

[MrDEB]

it is Q4 on the schematic.

 

[Nigel Goodwin]

Are you connecting external power to it?, and do you have that power on Vdd (Vcc).