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Ultra-Low Dropout Regulator

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There are many 1-3A LDO regulators which have excellt transient response and can cope with an automotive enviroment. I recently got a load of UCC283-ADJ form ebay. around 200mV dropout for 1.5A out....

The UCC283 family have an absolute max input of 9V and are not recommended to be used for outputs > 7V; hardly automotive :(
 
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eeek, whoops :D I tihnk I 'ma'y have confused part numbers there....damnit...I was ithnking of another chip I have...but thats has a whopping 0.9V LDO @3A...and that doesn't dorp much with current. (LD1084).

A sepic adds the complexity of a coupled inductor (not always the case) and linear tech have some pretty impressive controller chips for that.

If you're after convenience, then perhaps a prebuilt module switching reg and an LDO would be best, although its not always recommended, an LDO on the input to give, say 10V, then a boost reg for 12V. Not exactly efficient, but it'll do that job.
 
Try a MIC5209. I like them a lot, the only issue is a 16v Vin max but that shouldn't be a problem as it is being used like a LM317, so its gnd pin is at 7vDC which gives a Vin max of 16+7.
 
Anyone see anything wrong with using a 9v reg on the GND of the UCC283? I guess that would mean that the output could be temporarily switched to, which it see as, -6V, violating the pass elements maximum working VDS.

About your first design, that looks pretty awesome, if you're not overly worried about efficiency, a small charge pump with a 555 could be used so you could use an N-channel MOSFET as the pass element....although the transient reponse might suffer as the charge pump wouldn't be able to provide much current to cope with sudden changes in current through the MOSFET. I have seen some newer P_channel's with some very low on resistance...I'm sure your application could handle 11.9V when the battery is at 12V, with a 100mV drop at 2A, thats 50miliohms on resistance - doable with todays semiconductors.
 
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