2SK4066 2.7Mohms.

There are ones with a lower RDSON but really expensive.

 

2SK4066 2.7Mohms.

There are ones with a lower RDSON but really expensive.

No need to really go below 50 mOhms. Your 10W, 12 v lamp implies it is only drawing 0.85 amps or so.

That means a voltage drop of 0.010 ohms x 0.85 amps = 0.008 volts. And no heat (0.008V x 0.85 = very small number of watts.

Are you planning on PWM or just switching on for some time and off later? If Pwm, then gate capacitance is more important than ONresistance

 

Right now just on / off. But I might want to do PWM sometime in the future. But if the new light performs at least as well as the old then there is probably not a need. The old would go full intensity all night when the battery was just a couple of years old. Now that battery will be 5 in the spring so probably time for a new battery.

Which brings up another subject. The current light has no PWM current limiter. I added a buckpuck to my controller. I think I have it set to 620ma. I can bump that up to 700+ ma. The new light will have it's own PWM current limitation. Do you see and any problem with it driving the light? I realize it could not be as bright as it could.

And that is why I am here. In case I want to power the light direct. The buckpuck lets me turn the light on and off plus it provides 5V for my pic. Very cool. I already have the switching PS handled for the 5V. I just need the switch now. The module I will build will be plug compatible with the buckpuck. That way all I will need to swap the buckpuck out with my module.

 

Unfortunately it looks like it only comes in SMD. I would rather not deal with it unless I have to.

Digikey has a really cool metric for special feature FETs. One is the "logic level" feature. I found the 2SK4066. 4.7 mOhm @ 50A, 10V. Good candidate?

The MOSFETs on old PC motherboards are rarely less than 50A, typical is about 80A. The Vds is generally about 20 or 30V and most are pretty much logic level, even if the datasheet doesn't say it in so many words.

Most are SMD, but I usually find their outstanding characteristics sufficient motivation to build the leaded components around them - although I did recently find a scrap Dell PC with a few of the smaller MOSFETs in through hole format. I think they're TO251 package.