Quote:
Originally Posted by bojan
Depends on current and voltage drop.
P=U*I
where
U = voltage drop on control element (MOSFET or resistor)
I = current.
In your case, the dissipation will be ~6W, quite a lot - you definitely need heatsink to prevent MOSFET thermal destruction.
However, even simple resistor (capable of required dissipation, say 10W) will do, no need for MOSFET. It will get quite hot, though.
But, I am not quite clear what you really want to do here. Is it just a general question or you have some application in mind?
If you want regulated supply voltage, while the current is limited in case of short circuit, then you should use some of dedicated voltage regulator IC's (7812, for example) with built in current limiting.
The better way (lower dissipation, even when regulator is shorted at output) is to use SMPS IC's ( http://www.maximintegrated.com/produ...ng-regulators/) but for this approach, you have to have some experience with electronics... and the circuit will be more complicated.
http://www.jaycar.com.au/images_uploaded/LM2576.PDF
http://www.dimensionengineering.com/...ing-regulators
http://www.analog.com/static/importe...egulator_E.pdf |
Thanks Bojan for all the info. Very much appreciated.
The application is specific, in that I want to supply a camera, among other things, from a bus with regulated 12v, 3A maximum. Total system load, if everything were operating at maximum is ~ 7A. The SMPS is rated at 12v 12.5A.
The whole idea is to have one power source and distribute all power needs from a bus, instead of my current arrangement of several plugin adapters. The bus will be mounted on the dovetail - DEC axis.
The attached image is the basic idea. The loads are represented by resistors limiting to max current for the service, camera etc. That is, the 4, 12, 12, 12 and 17.9R resistors. There's also a variable brightness LED work light. The 5v supply switches the dew heater between max and approx half power through the mosfet - could be a pin from a micro controller.
The LM2576 looks like the ticket, although I will need several.