# Power switching with transistor

Hey everyone,

I thought this was a beginner forum, I'm very much a beginner and I have a very basic question. I need to switch a max of 2A @ 6Vdc and thought I would need a jfet based on my understanding, but I haven't been able to sort through the filters on the digikey site. I thought I could narrow it down by the case type, find a case type for the mounting style then power range and go from there. On digikey, they jump from mA to 35A and really high voltages. I can't find any pages on the google box that corrilate case type with power, which I thought was the main basis for different cases. Could someone suggest the correct filters or maybe an actual transistor?

very much appreciated

What is the switching load? Is it inductive? Resistive?

Joined February 12, 2018      696
Monday at 02:11 PM

Hi Sourav,

it's going to control power to a servo, so while the micro controller is idle (which will be weeks at a time) i can power it down and it's not going to try and hold position. so it's 5V DC with a stall current of 1800ma. the micro output to the gate is up to 5V.

Heath

Joined September 27, 2021      2
Monday at 12:25 AM

You can use 5A mosfets with low rds on resistance. THere are many in digikey.

Joined February 12, 2018      696
Monday at 02:11 PM

Thanks Sourav,

Joined September 27, 2021      2
Monday at 12:25 AM

Everything in this world having conenctivity has some sort of resistance. Now, when Mosfet act as a switch the current flows from Drain to source. This drian to source resistance is needs to be very low to achieve thermal efficiency and having a low size heatsink.

Suppose a Mosfet having 1 Ohms resistance between the Drain to source, it will produce heat of 5 x 5 x 1 (I2R formula) which is 25 Watt and thus having a larger size heatsink to disspate a lot of heat at 5A.

When a Mosfet at the same rating having 0.1Ohms or 100mili ohms resistance the power dissipation will be 25 x 0.1 = 2.5Watt which is 10 times lower than the previous one and the heatsink could be 10 times small than the previous one if you think from the linear mathametics terms.

Joined February 12, 2018      696
Monday at 02:11 PM