Source selection Circuit

Question

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.

This question has been asked many times before, you can use a diode selection circuit or pmosfets to select the source https://electronics.stackexchange.com/questions/96398/or-ing-power-supplies-diode-or-mosfet — Voltage Spike, Oct 19 '20 at 15:50

score 2 · Answer 1 · answered Oct 19 '20 at 16:02

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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.

answered Oct 19 '20 at 16:02

Kevin White

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Can you please suggest any IC from Analog devices – Puneeth Oct 20 '20 at 07:14
"Analog Devices" is the name of a semiconductor manufacturer. "analog devices" means that. "Analog devices" causes confusion. Capitals matter! – Transistor Oct 20 '20 at 08:34

vu2nan · Answer 2 · 2020-10-20T08:31:54.963

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Version 1

Only one Schottky diode would be required.

It is to be ensured that the voltage of 48 V_DC is always slightly higher than that of 48 V_Reg, for the former to reverse bias the diode and predominate.

Version 2

Only one relay, with a 48 V DC coil, would be required.

edited Oct 20 '20 at 08:31

answered Oct 20 '20 at 04:25

vu2nan

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In my application both voltages are exactly same.. – Puneeth Oct 20 '20 at 07:29
That should not be a problem in Version 2. – vu2nan Oct 20 '20 at 08:33
What if both voltages are present – Puneeth Oct 20 '20 at 15:06
When both supplies are on, the 'NO' contact of K1 will connect the output of 48 V_DC and its 'NC' contact will disconnect the output of 48 V_Reg. That makes 48 V_DC the dominant supply. – vu2nan Oct 20 '20 at 16:44

score 1 · Answer 3 · answered Oct 19 '20 at 15:38

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Without more information, I would recommend recognising 48V_DC as a logic signal to drive a single-pole double-throw switch such that if 48V_DC is 'on', the switch is connected to the 48V_DC terminal, and if 48V_DC is 'off', the switch is connected to the 48V_Reg signal.

answered Oct 19 '20 at 15:38

kanoo

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Are you suggesting a manual switch - if yes it is not recommended. If SPDT IC is used then for powering IC there is no power in board. Please let me know if you can suggest any IC – Puneeth Oct 20 '20 at 07:13
@Puneeth Non-mechanical (is that what you meant by manual?) switch I've used recently: shorturl.at/nrQ02, although I'm sure there are versions with only one spdt switch out there, rather than the three present on this IC – kanoo Oct 20 '20 at 13:59
Hey can you share the part number – Puneeth Oct 20 '20 at 15:05

score 1 · Answer 4 · answered Oct 19 '20 at 15:57

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you can use a relay for that, using the 48V_DC voltage as "digital signal"

when the 48V_DC is present, the relay is activated you have the 48V_DC voltage at the output,

the diodes make possible not to have a voltage drop during tansitions,

answered Oct 19 '20 at 15:57

Juba

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Hey can you please let me know which tool you used to draw above schematics – Puneeth Oct 20 '20 at 15:09
@Puneeth i use Cadstar (not my favorite) – Juba Oct 20 '20 at 15:22

Source selection Circuit

4 Answers4