I am using webbench to design a power supply and I am evaluating simple switcher and other switcher parts. there are about 20 of them and so it is a toss up of price v.s. board area v.s. cost, etc.. my question is all the designs have you type in a fixed load. in my case 5 A, and I want output of 12V to 0V. effectively. We are designing a heater control and instead of doing PWM with a transistor on 12V output to vary heat, we want to do varying voltage. 12V down to 0v. My question is i see on some of the designs it is not recommended that output goes less then 5 v. so how do I know which switcher chip is compatible with this kind of design. (other than just using a liner regulator which will probably get too hot?)
for the record power in is 24VDC, and output is wanted to be 12V @ 4A, (this is full on 100% power into 3 Ohm load for 48Watts) down to effectively 0 or perhaps low voltage of 3V @ 1A (3Watts)
On most of the switcher products, can you just add a variable resistor into the feedback pin to effectively make all the regulators Adjustable. If so, where is the gotcha point or failure point where I hit the device limits? (for example instability, or poor regulation, large noise output, or internal comparators and voltage references cant be overcome. )