The purpose of the comparators is to do some line supervisory. If the wire is cut or if it is shortened, the alarm goes on. Is there any simpler solution ? Most of the sensors accept voltages between 9V and 16V. So I think they could be powered from 13.8V unregulated. The battery could be charged with 13.8V with minimum circuitry (when it has reached the maximum capacity, stop charging, and when it has discharged under some value, disconnect it from the load). From the 13.8 unregulated, feed a 5V regulator. Did I understand correctly ? The values for current (3A for each) are the maximum needed values, the circuit won't necessary draw so much current. Lucian -----Original Message----- From: pic microcontroller discussion list [mailto:PICLIST@MITVMA.MIT.EDU] On Behalf Of Byron A Jeff Sent: 24 martie 2004 13:27 To: PICLIST@MITVMA.MIT.EDU Subject: Re: [EE]: 12V and 5V Power Supply On Wed, Mar 24, 2004 at 12:40:03PM +0200, Lucian wrote: > First, thank you all who replied to me. > > The comparators are feeded at the voltage provided as 12V, so if it is > 10V, they are feeded at 10V, so I think it could be a voltage drop > bellow 12V. As Jinx has asked in another post, take some time and explain the purpose of the comparators. Why are they in your circuit? What are their inputs? What are their outputs? The reason is that there's almost always another way to solve the problem. But right now we don't have enough information to solve the problem. > You suggested that I put the battery first, after the transformer and > the rectifier bridge, if I understood well? Yes. > Shouldn't it be some charging supervisory circuit there ? Maybe. If the output voltage of the transformer/bridge circuit is really 13.8V you can simply float charge the battery without any charging supervisor. However if the voltage is significantly higher than 14V under load, then at the very minimum you need a regulator to 13.8V followed by a current limiting resistor. But it is probably better to match the transformer/bridge so that the battery can be directly connected. Anything near 13.8V should be fine. I do apologize for not being clear. I was addressing the point that in your circuit that the battery comes before the regulators, not after > It's not very clear to me how the schematic looks if I admit that I > don't need exacty 12V, but it can drop to 10V. I still don't know why it is that you need the 12V or the 10V. If you can describe the purpose of the comparators, maybe it is possible to get this down to a single regulated voltage source. > 13.8V unrectified may power some sensors ? Isn't this dangerous for them > ? I don't know. What are the specifications on the sensors? Also the battery will serve as a form of regulator, as batteries tend to pull the input voltage towards its terminal voltage. I am still looking for more information. BAJ -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.