Choice of FET

[richard]

what about something like this, I used one to run my rollerdoor (12v windscreen wiper motor)


SP8K24FRATB 1 tiny soic8 contains two devices only costs a dollar

[Scampy]

Hi Richard, thanks for the suggestion.

In your application, I'm guessing that the current is switched long enough for it to get hot. If I was drawing 2 amps through the device (ie 2 amps per FET) at 12v for upwards of 6 hours would the device get hot? I've looked at the datasheet and it says something about 2w total power dissipation, but I confess my ignorance in translating that into real world instances.

Cheers

[Scampy]

Richard, having problems locating them in the UK - Only Farnell stock them, and as I have an account with RS would prefer to get something from them. This is the closest I can find on RS

http://uk.rs-online.com/web/p/mosfet...stors/8648710/

Would this suit my needs ?

[HenrikOlsson]

Looking at the Farichild FDS 8949 it has a specified Rds-on of 36mOhm (max) at a Vgs of 4.5V and 4.5A drain current.
36mOhm at 2A drain current equals a power dissipation of 72mW per switch or a ~150mW for both in the package.

The thermal resistance, when using minimal pads, are specified as 135°C/W so the package temperature will increase by ~20°C, it will feel warm but not hot.

Looks like it should work just fine as long as you keep the Vgs "up there".

/Henrik.

[Scampy]

Many thanks guys.. I'll sort out an order and do some real world tetsing

[MichelJasmin]

FDS6690A
Single N-Channel, Logic-Level, PowerTrench MOSFET

11 A, 30 V
RDS(ON) = 17.0 mW @ VGS = 4.5 V