Selecting one out of 2 power sources

Thread Starter

Surya1234

Joined Apr 23, 2021
20
Hi All

I am working on designing a system wherein module 1 is the main source driving a string of LEDs. If the module-1 fails to drive the LED strings due to any combination of the following failure, then module-2 (back-up) supply should take control and get connected to the LED strings only and not the driver-1.

Possible failures

1. 12V to module-1 is down
OR
2. Module-1 driver has a failure which its microcontroller is able to detect

Main requirements are
1. Power sources should not feed power to each other i.e. Current from module 1 shouldn't enter into module 2 and vice versa. This can be satisfied by adding a diode at the output line of each LED driver.

2. Voltage drop from driver-2 to LED strings should be as minimal as possible so we have to ensure whatever switches (transistors and MOSFET) we choose should have low on-state resistance.


1647897583187.jpeg

I appreciate if you can share what switches need to be added to module-1 and how they should be connected.
 

AnalogKid

Joined Aug 1, 2013
10,098
1. LED current - ?

2. If the 12 V to module 1 fails, the uC has no power to control the electronic switch.

Other than that, a p-channel MOSFET will do what you want - IF - the uC can turn it off quickly when module 1 resumes driving the LEDs. If not, then Linear Tech makes "perfect diode" or "ideal diode" control chips that monitor the voltage across the FET and turn it off very quickly when the voltage reverses by a few millivolts. Does the uC control the electronic switch?

3. LED current - ?

ak
 

Thread Starter

Surya1234

Joined Apr 23, 2021
20
Can I use a depletion MOSFET which gets turned off when the microcontroller 1 is ON and it wants the driver 1 to turn on the LEDs and when the microcontroller-1 loses its power (because its 12V supply is off), the depletion MOSFET control signal is lost and the MOSFET goes back to its default ON state which connects module-2 to the LEDs?
 

Thread Starter

Surya1234

Joined Apr 23, 2021
20
1. LED current - ? are you asking about how much currents the LED string will draw?

2. If the 12 V to module 1 fails, the uC has no power to control the electronic switch.

Other than that, a p-channel MOSFET will do what you want - IF - the uC can turn it off quickly when module 1 resumes driving the LEDs. If not, then Linear Tech makes "perfect diode" or "ideal diode" control chips that monitor the voltage across the FET and turn it off very quickly when the voltage reverses by a few millivolts. Does the uC control the electronic switch?
Yes, I am thinking of controlling the switch from the microcontroller-1 unless I find another solution where it doesn't have to.

3. LED current - ?

ak
 
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