Low RDS logic level N channel MOSFET

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1

Hi All,

Currently going crosseyed staring a datasheets and was wondering if anyone can help

I'm after a logic level (3.3v) low RDS (<10milliohms) N channel MOSFET for controlling 850mAs worth of LEDs at 12v. The circuit will be used to switch on/control the brightness of the LEDs.
10-bit PWM @1khz (esp8266)
Due to space constraints ideally I'd like something smaller than the usual TO-220 package. Either through hole or smd.

There's so many options i'm going nuts :o Do people have a go to for this type of application?

Regards

Ollie

2

Or would I be better off using a MOSFET driver ie, MC33151PG https://docs-emea.rs-online.com/webdocs/1251/0900766b8125102d.pdf and using the 12v to power the MOSFET gate.

3

There are tons of option. Go to digikey catalog, use the filters. At that current, there's stuff in sot23... 10mohm might be hard, but you really dont need it that low, and tens of milliohms is easy.

4

DrAzzy:
There are tons of option.

That's the problem lol

I've been on the RS website all morning and feel even more overwhelmed than when I started. Do have a recommendation for a max RDS?

5

Say you want to dissipate < 100mW. That's about 1% of the load so efficiency > 99%.

Current is 0.85A

Then Rds max is such that 0.85 ^2 * Rds is < 0.1

I'll leave you to do the sums

Allan

6

allanhurst:
Say you want to dissipate < 100mW. That's about 1% of the load so efficiency > 99%.

Current is 0.85A

Then Rds max is such that 0.85 ^2 * Rds is < 0.1

I'll leave you to do the sums

Allan

Thanks :slight_smile:

So I'm looking at around 140mOhms max RDS if my maths is correct.

0.852 * 0.140 = 0.101

I think I've settled on FDC655BN. Should fit my needs. https://docs-emea.rs-online.com/webdocs/10e2/0900766b810e24f3.pdf

7

OllieNZ:
I'm after a logic level (3.3v) low RDS (<10milliohms) N channel MOSFET for controlling 850mAs worth of LEDs at 12v. The circuit will be used to switch on/control the brightness of the LEDs.

There are no 12volt LEDs, so what do you mean with that.
Is this a LED strip, with current limiting resistors fitted.
Or do you need to add CL resistors yourself.
Post a link to the LED(s).
A string of three white LEDs could have a Vf of 9.5-10volt, so ~2volt needs to be dropped, with e.g. a resistor.
That resistor should be (12-10)/0.85A= ~2.35ohm.
Rsd(on) of the fet is insignificant compared to that.
Leo..

8

Wawa:
There are no 12volt LEDs, so what do you mean with that.
Is this a LED strip, with current limiting resistors fitted.
Or do you need to add CL resistors yourself.
Post a link to the LED(s).
A string of three white LEDs could have a Vf of 9.5-10volt, so ~2volt needs to be dropped, with e.g. a resistor.
That resistor should be (12-10)/0.85A= ~2.35ohm.
Rsd(on) of the fet is insignificant compared to that.
Leo..

It's a pre-existing off the shelf setup for an aquarium, unfortunately the way the existing controller (S3F94C4EZZ-DK94) is programmed to operate means the light unit is not suitable for use with a timer.

I'm attempting to replicate the existing dimming circuit but can't identify the MOSFETS used so I have no idea if they're suitable for use with the esp8266 or not.

9

I think it will work fine. You aren't asking much from it.

One word of caution, look at Figure