Powering from the vehicle 12v

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OK, so I know about the various horrible things that vehicle supplies can do. (Although I believe that newer cars are probably a lot better). I tried one 'automotive' IC, but it had a voltage bump on startup, soI just went with my own battery supply for now.

 

Then I wondered about USB chargers as a source. They are fairly popular, but I wonder if they do supply a constant 5v or if they are depending on  having a reasonably stout battery as a load.

 

Thanks,

 

hj

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Are you talking about USB ports in cars, or USB chargers, generally?

 

My relatively new Subaru has both full USB ports as well as a couple of USB charging connectors. Don't know how clean they are, power-wise. 

 

I've heard that the $5 wall outlet plugin chargers can be pretty bad, noise-wise. Also, be aware that USB 5V, generally, can be from around 4.5V  to maybe 5.3V and still be "legal". 

 

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

Last Edited: Tue. Mar 26, 2019 - 04:36 AM
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A bump? I would expect a dip as the moment the car is started the battery gets to turn the started engine which is a lot of amps so the voltage will drop significantly.

I would treat the 12V car supply as well as pluginchargers as a non stabilized supply, so you need to make sure you have a regulator in between.

USB can also not be trusted as it (as jim already said) can be from 4,4V to 5,3V so also there you need to have  a regulator.

The power banks most likely will have a switched mode power supply to get the Lipo voltage to 5V all across its working voltage range(3,2V - 4,2V) They should be made to specification so if the bank states to ba able to deliver 1Amp from a port it should do so while keeping the voltage more or less at 5V. Not sure about ripple though, but that would just be a matter of also not trusting that and make sure you haev your own regulator to ensure that what you define as being 5V on your PCB is actually 5V no matter what is input.

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OK, sounds like a bad idea -- I was just hoping

 

Thanks,

 

hj