Hello Everyone,

I want to design a circuit similar to this one, which can switch to battery power in case of mains failure.
My requirement is very simple. Here's a simple battery charging circuit, driven by 5V supply.
I would want the 3.3V regulator to be driven by 5V supply in case there is power & through Vbat in case of power failure.

The one question I have about the reference circuit is that it shows 12V supply to the gates, in my case the supply would be from Vbat which is like 3V - to 4.2V. The datasheet shows the G-S voltage to be 9V

Regards,
Chaitannya

 

Something like this with low Vf schottky (not silicon) diodes (ignore source voltages) -

Something like this - http://www.onsemi.com/pub/Collateral/NSR0320MW2T1-D.PDF

What current do you need for load ?

Regards, Dana.

 

OK,
This should work, that was the first thing I had thought of but the only conern is, is it used in practical circuits. Are their any disadvantages of using it over MOSFET.

Regards,
CHaitannya

 

Yes, MOSFET circuits can get close to 0 Vdc drop across them, incrementally
giving you a little more battery/circuit lifetime. Also they can exhibit more isolation
when off depending on device used.

Regards, Dana.

 

Are their any disadvantages of using it over MOSFET.

The MOSFET does have a much lower forward drop but it requires additional circuitry to control the gate of the MOSFET.
Here's an example circuit.

 

See

 

The MOSFET does have a much lower forward drop but it requires additional circuitry to control the gate of the MOSFET.
Here's an example circuit.

Correct. fitted in one chip lm5050
I used it very often.

Picbuster

 

See

Is M2 in backwards?

ak

 

Is M2 in backwards?

ak

Yes. The only way! Otherwise, we get two series-connected diode.