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Dual power supply: solar cell and a battery

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Hi everybody!

Could somebody help me? The problem is: I need to feed a circuit with some values of supply: 5V, 3.3V, 3.8V and 1.8V. Some ICs need 3.3V, only one IC needs 1.8V, another one needs 5V and another needs 3.8V.
Then, I have two sources of power: a +12VDC which comes from a solar cell and another one which comes from a +3.7V battery. I want to feed the whole circuit with the solar cell power. But, when it's night the battery has to supply the circuit. When there is daylight again, the battery has to be charged through the circuits by means of the solar cell power. How can I make this circuit?

I hope my explanation was enough clear. If not, please say to me, I try to explain in other words.
Thanks in advance.
 

Re: Dual power supply

One way:
.
Diode "OR" the solar cell and battery supplies. Convert the "ORed" voltage using a buck-boost switching regulator for the 3.8V, 5 V supply, and buck regulators for the lower voltage outputs. Depending on the regulation requirements, you might get away with multiple winding regulators with feedback taken from the output voltage with the most critical regulation requirements.
 

Re: Dual power supply

Have a look at the attached conceptiual diagram of multivoltage system.
At this early stage it is an open system and another blocks can be added or modified.
The main idea is to generate one common voltage, say 5Vdc from both power sources, and switching 5V on/off depending on coditions (night/day) with a couple of p-channel mosfets (low channel Ron).
Depening on current demands from 1.8, 3.8 or 3.3 you can employ another SM dc/dc converters. Hugh selection of high-efficient dc/dc converter you can find at Maxim-IC (www.maxim-ic.com). If current required is small (some mA) you can even consider simple rezistor/zener diode regulation ..
Here is an example of your main 12V-5V step-down converter based on MAX1627:
**broken link removed**
Rgards,
IanP
 

Dual power supply

How vaule Volt batt to charg?
 

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