A circuit to make regulators go to 0v.

[VEGETA]

I've looked into it further this day and I figured out how to use the current limiting feature by supplying 0-1v on I_CTRL pin. 0 -> 0A and 1 -> 2.5A. However, I guess this is fixed current or current source rather than current limit... I tried the circuit numerous times on LTSpice (newer edition!) and this is what I got. I say that because the voltage drops to certain level in order to regulate the current properly.

Another issue is that the current set is not accurate, my guess is the 1.4uA current source near the I_CTRL pin (similar to TR\SS one) which charges the capacitor. I am trying to make an offset by a current source from 3.4v ref to the required place... I think it is the sensing resistor pins (diff amp) but I will try putting it on the I_CTRL pin itself.

What you pointed out in your figures up there is the inductor switching current not the load current... if the load current is reasonably nice, then no problem.

I am curious to know how do you limit the current using your method? is it current source or current limit?

[VEGETA]

I looked at this expensive device: LT3649 (http://cds.linear.com/docs/en/datasheet/3649fa.pdf)

It is one of these rail-to-rail switching regulators that offers TRUE 0v output because they use the same current source reference in their gain amplifier as the famous LT3081 and his siblings.

It is a massive 12$ device so not very economical! However, the other solutions like LT8611,14,40-1 are around 9$ so they are the same. The difference here is that LT3649 can be controlled straightforward more than the others... no tracking no negative supply... nothing, which is a big advantage. The other rail-to-rail regulators are only 15v max output which cannot do the 25v I want (this one 60v max! @ 0.5v drop @ 95% efficiency).


It offers current control and monitoring! so it is a power supply in a package. Control method is so easy, only resistor feedback. I still don't know if it is constant current (fixed) or just limit. very important to know.

I aim to make the lab supply capable of constant voltage, constant current source, current limit , and if I could constant power. To compete other designs because the price is gonna be a lot thanks to 12$ device.

Another solution that I came up with is the use of cheap high current pre-regulator followed by an efficient LDO that goes to 0v such as LT3083 @ 3A. However, this device itself is not cheap too (8$)... even LT3081 is not so cheap (5$) and offers only 1.5A and it is not an LDO so paralleling 2 of it is not efficient and will require a heatsink... I don't want to use any heatsink at all!