Electronics > Projects, Designs, and Technical Stuff
Good cheap way to get rock solid 12V DC output?
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Siwastaja:
The manufacturer helpdesk just cannot help you because they don't understand the matter, and don't have resources to get the engineer to talk to you. "Rock solid" is meaningless. If they won't give you an actual figure or graph, it's all just random babble.

The product is, of course, just fine even with varying input voltage from the li-ion battery directly. The battery is much better because it won't have that much ripple voltage than their AC adaptor probably has. The fact it changes slooooowwly doesn't mean a thing, if any of the voltages is acceptable on their own.

(This is a guess, of course, based on experience, but it holds 99.9% surely; we can't guarantee there isn't some super weird trap. For example, they may have implemented a voltage watchdog on purpose, which detects your "non-rock-solid" supply and refuses to work, calls NSA, or makes demons fly out of your grandma's nose. But, this is the unlikely scenario.)

In any case, the answer to your original question is, yes, any DC/DC converter is fine as long as it meets the ripple specifications by the manufacturer. If the specs do not exist, then... I guess the power isn't very important :). It will be locally regulated on the product anyway, unless it's complete shit.
Wolfgang:
Yeah, get a low drift reference (e.g., REF02), some quality op amp (e.g., LT1028), a pass transistor (2N3055) on a proper cooler, low-tolerance resistors (0.1%) and a proper compensation - here we are.
IanB:
One way to define "rock solid" is that the supply should be "stiff", meaning that the voltage remains stable in the event of load fluctuations. One of the stiffest supplies is a battery with low internal impedance. A lead acid accumulator meets this definition, but a high capacity lithium ion battery can also be have a very low impedance. Adding a regulator after the battery may ironically make the situation worse, since a voltage regulator may have poorer regulation in the event of sudden load changes than a battery by itself may have.
spec:

--- Quote from: IanB on November 27, 2018, 05:19:55 pm ---One way to define "rock solid" is that the supply should be "stiff", meaning that the voltage remains stable in the event of load fluctuations. One of the stiffest supplies is a battery with low internal impedance. A lead acid accumulator meets this definition, but a high capacity lithium ion battery can also be have a very low impedance. Adding a regulator after the battery may ironically make the situation worse, since a voltage regulator may have poorer regulation in the event of sudden load changes than a battery by itself may have.

--- End quote ---

Yes, of course, that is why I said to make a standard regulator 'solid'.

By the way, batteries can supply big gulps of current, but their voltage is not stable and they are noisy.
IanB:

--- Quote from: spec on November 27, 2018, 05:34:48 pm ---batteries ... are noisy.
--- End quote ---

Can you elaborate what you mean here? In what sense does the output from a battery contain noise? I think if I put a battery on an oscilloscope I would see the flattest line I could imagine.
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