looking for best solution

[elec4fun]

Hello,

I need -5v, 5v and 3.3v power supply on my board (about 300mA on 5v, 20mA for 3.3v and -5v is just for amplifier). Do you know if I have a chance to find a linear regulator or DC/DC converter with this kind of output on a single device ? if not, what is the best solution ? Linear regulator for 5v and 3.3v and an inverter for -5v ?

thanks.

 

[flatulent]

There is no single ready made solution I know of. If you make your own switching regulator you can get any set of outputs you want.

If you are making just a few copies, it is cheaper to buy than to design. I suggest starting with the highest power (5 V, 300 mA) and derive the other two from that. The 3.3 V can be had with a linear regulator. The -5 V from a switched capacitor inverter. These last two will have example circuits you can copy from the part data sheet.

 

[elec4fun]

Thank you flatulent, it is what I thought. I will do that with classic 78XX and a capacitor inverter.

 

[flatulent]

The 78xx may not have enough headroom. Use a more modern low dropout type regulator.

 

[elec4fun]

I don't understand "headroom" (I'm french, sorry for my english). Are you talking about the gap between 5v and 3.3v ? I think you're right, I had not thought of it, I will looking for another kind of regulator.

 

[flatulent]

Headroom is a more recent English word. It goes back to 1851 to mean the space between your head and the top of the doorway. Prior to that and to as early as 1570 it meant open fields and land. This word is totally invented in the English language. It is not adapted from another language.

The more recent definition was taken into electronics to mean the additional signal level that could be accommodated by a circuit without distorting or not functioning properly.

 

[carrier]

what is input voltage on your board?

 

[elec4fun]

Thank for precisions flatulent. I sayed silly things, the input voltage will be the 5v from the USB (in my mind it was 9-12v from transformer), so I have to only make 3.3V and -5v from 5v. I have found a lot off low drop out voltage regulator for the 3.3v and I will looking on analog devices, ltc or maxim for the inverter.

 

[layes2]

use land c dc-dc
or you cannot get the result