Steady 12V Supply From Car Battery

It is quite well known that a "12V" vehicle battery will fluctuate in voltage level between, roughly 11V - 14.5V, during the general running cycle. Trasient high voltage spikes are also known to occur and can damage sensitive circuits.

Im quite surprised that I cannot find a "tried and trusted" method to gain a regulated 12V constant output voltage circuit?

My requirements is 12V at low current (<1A) for simple logic circuit. A Ripple of <0.5V will be considered decent.

Can anyone recommend a low cost method of achieving this?

Regards,
StudentSA

National's WebBench designer shows the LM3478 in a suitable circuit with an estimated cost of $4.19. Their example with the LM3488 has a total BOM of $3.31.

mneary said:

National's WebBench designer shows the LM3478 in a suitable circuit with an estimated cost of $4.19. Their example with the LM3488 has a total BOM of $3.31.

Click to expand...

Nice...bout time they put SEPICs into WebBench... I have been using the LM3488 as a SEPIC for a long time and did not have the benefit of WebBench.

Does it matter if the voltage occasionally drops below 12V, as long as it doesn't exceed 12V?

How much current is needed?

If it's just a few A then you could use a low drop-out linear regulator.

https://www.electro-tech-online.com/custompdfs/2010/05/KA378R12CTU.pdf

On page 17.28 of the ARRL 2009 Handbook for Radio Amateurs is a switched mode power supply that addresses those concerns. Current handling is far in excess of your requirements but I felt it worth mentioning. You can purchase commercial equipment that does the same thing.