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I remember seeing a clever circuit in which the voltage divider for an LM317 was referenced to -1.25 volts, allowing the output to go all the way to zero. The design also had a negative regulator that used the same trick.
There are not a lot of uses for power supplies that can do down to zero, are there?
I agree that it sounds like a bit of an oxymoron, but there are times when it is useful to be able to turn the voltage up from zero or down to zero.
Usually when trying to assess the start-up or shut-down behaviour of some circuit or device.
In fact, in the last year or so I did build a small PSU for injecting 0 to 10v DC test signals into a circuit.
JimB
PS, and here it is...
Wow, two years ago.
Doesn't time fly when you are enjoying yourself?
The ZPD's will get hot drawing the same load as output. 3x Si diodes could be better if they were fwd biased unlike reverse as shown.?
My Simulation https://tinyurl.com/2fm3bsbk > 700 mA may overload my model. The negative bias diode ripple is thus added to the output. Crude, but works. (noisy ripple) It might be better to make a bipolar supply then use a regulated Adj current to maintain the 1.25V across ADJ to OUT
Look at the picture, you will see that there are three 1N4148 diodes where the two "zeners" were drawn on my original scribble.
700mA is way more than my "DC Signal Source" is intended to supply, a milli-amp is more than enough.
And it worked well for the application I required at the time.