3.3 and 5 volt power

kt88seamp

One of my future projects will have a propeller chip and other ICs that require 5 volt power. The final result will have all components in surface mount. Will this 3.3 regulator work with the propeller (mouser part 595-UA78M33CDCYG3)?·Do I have to use the 400mA·one that parallax sells.

I noticed in the lab kit the 3.3 volt regulator is connected in series with a five volt. Why is this?·In my application I want to put them in parallel.·Do you guys have any concerns doing this?

Leon

Both are OK. There was some discussion on this forum recently of the advantages and disadvantages of the two approaches.

Leon

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mctrivia

the disadvantage of putting in parallel is the 3.3V regulator will have to disapate more power then if in series. efficiency will be the same both ways.

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ManAtWork

How high is your unregulated voltage and how much current do you need? If the source voltage is not too high and 100mA is enough for both 3.3 and 5V then a 78L05D and an LM317LD (in parallel) will do. Both come in SO-8 packages. The LM317 has the advantage of beeing quite cheap ($0.15). But if you want to power the 3.3V regulator from 5V you need a low dropout (LDO) type. For example an LP2951-M33 which is a bit more expensive (~$0.50).

If your input voltage is higher than 9 or 10 volts I'd recommend using a switching regulator for 5V and an LDO for 3.3V. Google for national semiconductor's "simple switcher". There are also chinese copycats that cost half of them (as always...)

Cheers