Need help on dual voltage circuit

[richloo]

Hi guys, need ur help urgently. I have a buffer circuit need to be operated in either high voltage or low voltage supply. My question is, what kind of mechanism can I use to switch from one voltage supply to another? since i have 2 supply on chip. Thanks in advance.

 

[IanP]

Try the concept from the attached picture..
Regards,
IanP

 

[richloo]

Thanks IanP. Do anyone have the internal circuit architecture for LM317? Sorry I still can't get the concept. It seems to me that this method is to create bit controlled voltage supply from a single supply Vi.
How about if i have 2 external voltage supply? What mechanism can i use to route either one of this voltage supply to my circuit?
Thanks in advance.

 

[IanP]

Internal architecture of the 317 voltage regulator you will find in its data sheet.
**broken link removed**
Other option (for 2 external voltages) is to use two P-channel mosfets, for example IRF5305 ( http://www.irf.com/product-info/datasheets/data/irf5305.pdf ), and just switch them on and off accordingly to needs through a couple of inverting gates (open collector) or transistors, so if one is on the second is off and the opposite way around. Have a look at the attached diagram..
Regards,
IanP