I need to put 12A through a small piece of metal (for soldering). Thought of a mosfet constant current source. Does anyone have asome parts and configuration for this application. Could use low voltage.
Basically, we are trying to solder a very small ferrule (metal cylinder) of about 15mm onto a metalized optical fiber (OD is 125 microns). There is a small solder ring that will be placed on top of the ferrule. The plan is to have two electrode collars from top to bottom and pump about 12A of current through (.09 Ohms) and heat up the ferrule, thus flowing the solder inside of the ferrule.
We have modeled a CCS using some mosfets and a bipolar transistor. My peer thinks that I'm crazy to use audio amps as a knowledge source. Now, he's convinced.
You've got a good point, Circlotron. On the other hand, I did just ask for somebody to need my obsession with constant current sources (I'm no expert, just crazed). However, what you want is just a little beyond what I've already drawn the PCB for. Most light and moderate requirements would be satisfied by a symmetric complementary arrangement. That may be the case here as well. While not of high precision parts, it can be fine tuned if you aim low and add resistors in parallel to reach your target current. The exact parts are not critical. You may only need two diodes per side for the transistor bias, depending on their forward drop and a few other things. This arrangement has a dropout about equal to all the diodes in series. There's plenty more I could say, but you have one from each camp.
Thanks for all of the feedback. The circuit drawn by Anthony is very similar to the one we chose. For a piece of automation equipment, we need it to be repeatable and reliable. Also, we need to be able to change the current based on process recipes. We are testing today.