integrated-circuitpower
I am doing a project, in which there are two dc source a) 48V_ DC b) 48V_Reg to power the board.
If either of two is present, that power source will power the board.
If two power source is also present then it should select 48V_DC
Please let me know any IC or circuit in where I can implement above features.
There's likely no need to use a voltage divider; plenty of MCUs are capable of using the internal reference as the input and the supply as the reference. For instance, on the ATmega328P:
ADMUX &= ~(_BV(REFS1) | _BV(MUX0));
ADMUX |= _BV(REFS0) | _BV(MUX3) | _BV(MUX2) | _BV(MUX1);
Then you can reverse the equation for the ADC count and solve for voltage:
\$ADC = {{1.1\text{V} \cdot 1024} \over V}\$
\$V = {{1.1\text{V} \cdot 1024} \over ADC}\$
Or if you don't need an exact value then you can set thresholds and compare directly:
\$ADC_{th} = {{1.1\text{V} \cdot 1024} \over 3.4\text{V}}\approx 331\$
This is my quick take on the circuit.
simulate this circuit – Schematic created using CircuitLab
Decoupling capacitors have been added.
The battery switch MOSFET has been made functional; When neither VUSB or DC+ are present R1 pulls the gate of the MOSFET to ground. This turns it on, allowing the LiPo to discharge into Vout without a diode voltage drop. C3 is there not only for decoupling but also for bridging the gap in the output when the circuit transitions between internal and external power. When DC+ or VUSB is provided, the MOSFET turns off as the gate voltage goes positive.
The CHG (charge) LED illuminates when /CHG is low (when the battery is charging) and shuts down when it is full.
The EXT (external power) LED illuminates when either VUSB or DC+ is present, turning off when on battery power.
The MOSFET needs to be a P-channel, enhancement mode power MOSFET with an adeguate current rating for the load and a treshold voltage (AKA Vgs) of -2.5V or better (closer to zero), or it won't turn on.
Keep in mind that LiPo batteries die if the cell voltage falls below 3V: you need to make sure that this never happens.
Best Answer
This is a common requirement on telephone or wide area network equipment and servers.
The most straightforward way is just with a pair of diodes. No active devices required.
Solutions such as relays have the problem that there will be a power drop-out while switching over.
IC vendors such as Analog Devices have more sophisticated solutions that also support hot-plugging and avoid the voltage drop of diodes.