I have to take 12Volts from acar battery and power a device with no more than 5 volts fairly steadily. I have always thought 7805 regulators to be avery energy inefficient way of doing it due to the wasted heat generated .

I have assumed that those regulators behave as a 5V zenner diode where the excess voltage is just shunted to ground almost like a light which gets brighter the more energy goes to ground. Perhaps thats my answer to use that shunted voltage to do something .

So does anbody have any suggestions as to an efficient wayto get 5V ?

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In a zener regulator it isn't excess voltage that is shunted to ground, it is excess current.

A zener regulator will take a constant current, usually a bit more than the maximum current that the load will take.

I think of it like a fixed valve filling a cistern with an overflow.

A series regulator like the 7805 blocks the excess voltage. The current it takes is about equal to the load current, and varies as the load current varies.

I think of it like a ball valve filling a cistern.

A buck converter can output more current than the input current. The no-load current is often a bit more than the no load current for a series regulator.

The choice of regulator type depends on how much current the load takes.

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A simple buck converter will work well for you.
Here's a link another user here provided to me ages ago that should be a drop in replacement, depending on your current needs.
Complete circuit and component listing for a 14V to 5V regulated buck converter. A zener is used as a voltage refrence so it can actually be set to any desired output voltage in range.
2-transistor Black Regulator

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If you want a quick easy solution, look at a Recom regulator.

R-78xx-0.5 - The smallest 7.5 Watt switching regulator - RECOM

I use loads of these, 26V In 5V Out @ 500mA max.


Jim

 

Thanks -things have changed . That RECOM device looks good . Now to see if I can get them in OZ

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My Property and my Family are not for Govenments to control.That is not the purpose of Governments.
To stop corruption in Government officials give them three times the penalty. They should, and do, know better. Let them commit to that when first employed

 

RS should stock them

Jim

 

Phwew $15 each , I ordered 1

__________________
My Property and my Family are not for Govenments to control.That is not the purpose of Governments.
To stop corruption in Government officials give them three times the penalty. They should, and do, know better. Let them commit to that when first employed