[chbot] noob mosfet/transistor question

[Andrew Dachs]

Chiming in mostly because I’m another Andrew.

Don’t really have a favourite but what you describe is very common. If you can use a switch in the ground line (low side switching), a single mosfet and a diode for protection would be nice and simple. Assuming you are looking to turn this on/off at some slow rate, just look for a FET with low Vgs (some are called logic level mosfets) and enough current capacity with plenty of margin (the max current quoted in the specs assume heatsinking). 

A disadvantage of low side switching is you leave the high side voltage active all the time and there might be a risk of shorting. 

Andy


Sent from my iPhone

> On 24/05/2021, at 11:44 AM, Mark Atherton <markaren1 at xtra.co.nz> wrote:
> 
> Hi Andrew,
> 
> Please tell me more about your 12V load.
> 
> Is the 0V or the 12V power rail common to all of the devices you are driving ?
> 
> If you use a common 0V rail, the whole issue is much easier using an N-CH FET with 5V (min) gate drive.
> 
> -Mark
> 
> 
> 
>>    Short version: What transistor/mosfet / resistor would you use to
>>    switch 9-13v 100-300ma from an arduino?
>>    Long version:
>>    I’ve had great success with a “prop hub/master controller” I
>>    designed, but keep running into a mental wall trying to make the
>>    next generation.
>>    In a nutshell, its a breakout for an arduino with a dozen rj45 jacks
>>    to power and control remote props.    I have been trying to put a
>>    transistor inline with the 12v output to each remote prop so I kill
>>    power to each remotely.
>>    I have the free pins on the arduino and I know basically how I’d use
>>    the transistor/mosfet to switch, but I’m lost as to exactly what
>>    transistor/mosfet to use.
>>    The switched voltage would be between 9 and 13v, and I reckon the
>>    maximum draw from any device would be maybe 300ma?
>>    Does anybody have a favorite transistor for this application (where
>>    the gate is 5v and the throughput is 12v, and the 5v from an arduino
>>    would saturate the gate)?  I was thinking maybe the transistor would
>>    be “closed” when the arduino went high, and switch off when low… but
>>    it could easily be the other way around if that’s a simpler circuit.
>>    Any wisdom appreciate!
> 
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