Electronic Power Switching

[mitz]

Hello dear guides,

I thought of designing a power backup system. During mains failure the system switch to battery. To avoid the relay switching time, I thought of power switching by MOSFET and then through relay. MOSFET will be switched off then. Micro controller based design. Pls refer the circuit provided. Can you pls help me. Thanks.

Schematic image : https://obrazki.elektroda.pl/2307208800_1356866884.jpg

Circuit Simulator link of the schematic

https://www.falstad.com/circuit/#$+...795+423+0+12+common+ground+to+all+appliances

 

[chuckey]

The easiest way to to connect the kit too the battery and just charge the battery of the mains. If you really want to use a relay, just use a large capacitor across the load to maintain the voltage while the contacts of the relay make. N.B. you must have a sensitive mains voltage detector, isolated from the load and capacitor with a diode. this so when the incoming +12V falls by ,say, .1V, the relay operates, so you need a proper reference and amplifier to drive the relay.
Frank

 

[mitz]

The easiest way to to connect the kit too the battery and just charge the battery of the mains. If you really want to use a relay, just use a large capacitor across the load to maintain the voltage while the contacts of the relay make. N.B. you must have a sensitive mains voltage detector, isolated from the load and capacitor with a diode. this so when the incoming +12V falls by ,say, .1V, the relay operates, so you need a proper reference and amplifier to drive the relay.
Frank

Thank you Frank.
Meanwhile I thought of using a FET in common emitter follower mode.

Just in case if you like to look at it...

Schematic url : https://obrazki.elektroda.pl/1113090800_1356958063.jpg

Circuit simulator link : https://www.falstad.com/circuit/#$+...ttery x+180+282+266+285+0+12+Rectified+mains

 

[chuckey]

Your transistor is shown as a junction type, so with 12.8 on its emitter, the base potential will be 12.8 +.8 = 13.6 V, the Vc = 15 V, so there is 1.4 V across the 220 ohm resistor so the current through it will be 1.4/220 ~ 6.5 mA, the collector current as shown is 6.5A, this means that the transistor has a gain of ~1000, a bit high I think. if its a darlington, then the Vbe is 1.6 V, so the volts across the 220 ohms will be .6V so the current will be .6/220 ~ 2.7 mA, needing a current gain of 6.5/2.7 X1000 = 2500? still high for a darlington.
Frank

 

[mitz]

Your transistor is shown as a junction type, so with 12.8 on its emitter, the base potential will be 12.8 +.8 = 13.6 V, the Vc = 15 V, so there is 1.4 V across the 220 ohm resistor so the current through it will be 1.4/220 ~ 6.5 mA, the collector current as shown is 6.5A, this means that the transistor has a gain of ~1000, a bit high I think. if its a darlington, then the Vbe is 1.6 V, so the volts across the 220 ohms will be .6V so the current will be .6/220 ~ 2.7 mA, needing a current gain of 6.5/2.7 X1000 = 2500? still high for a darlington.
Frank

Thank you Frank.

When I thought of using transitor combined with relays, I did a quick simulation to check if it works to my circuit expectation. All values of components are just for simulation testing only.

Thank you again for the valuable suggestion.