I am revisiting a problem that was posted a few months ago. I have tried numerous solutions, but nothing on the complex side of things will work for this application.
The problem is that I need to be able to convert an input voltage varying from 20 volts to 80 volts (at up to 100 amps) to 12 volts (at
500ma to 1 amp).The recommended solutions in the past were not small or cost effective. This needs to be something that can be done with just a few SMT components. Size, weight, and cost are all important.
Using a simple Zener/resistor regulator works fine for a preset voltage (where the resistor value can be calculated correctly). The problem with this arrangement is that if the input voltage is 80 volts and the resistor is chosen so that 500ma of current is available, if the input voltage drops to 20 volts the current becomes way too low to be usable. Setting the current correctly for 20 volts results in extremely excessive current (and fire) when the voltage is 80 volts.
Is it possible to use some sort of transistor with the zener to limit the current based on the voltage? Some type of follower circuit? A schematic of this would be handy. I seem to recall seeing something like this a few years ago, when I didn't need it. :)
Thanks!