Switch to Battery Supply when Main Power Fails

[yviswanathbe]

Hi Friends,

Can some body suggest me an IC which can keep track of MAIN SUPPLY and when power fail occurs, it should automatically change to Battery Supply.

Please send some reference schematics.

Thanks and regards,
viswanath

 

[nashwan]

hi
i think u need a circuit like used in UPS system

but in simple way to detect main power fails is use ac relay accros main power
supply with same rating voltage and used contacts for relay as change-over

u must explain more abt ur project ...type of load...batt capacity..etc

 

[Tahmid]

Hi,
Mains sense can be done in many ways.
You can use a bridge rectifier at the input and use this to turn on an optocoupler (4N35, etc). Use the output from the optocoupler to control the relay or control circuit.
You can also use specialized optocoupler like TLP620 which can directly be driven from mains as there are two "LEDs" inside this optocoupler and hence both mains phases can be detected.
Or you could rectify the AC to DC, use a voltage divider and then feed this into a transistor.

This is the mains sensing part. Each of these will give either a 0 or 1(5 or 12volt, depending on your circuit) depending on your circuit configuration. What you must next do is, decide how to use this signal to switch to battery supply.

You could use a relay, which would be easiest, such that the relay turns on when mains is absent, and consequently turns on the oscillator when mains is absent.

Hope this helps. If you require more help, I can try to explain further.
Tahmid.

 

[millwood]

get a single strand wire, and wind it on the mains and link it to your mcu.

if you detect pulses on that wire, you have mains power.

ie: the winding acts like a current sensor.

 

[yviswanathbe]

Hi Friends,

Thanks for the responses.

Let me explain my application, The user will select a configuration from the LCD, and will test continuously for hours(min 10hrs). During testing if power failure occurs i need to store the current test configuration in the memory and after next power on i should continue the same test.

As my micro controller internal Flash endurance is limited i cant store the data every second. The Time taken for writing to the Flash is approx 50ms.So i need to implement a circuit for detecting the power fail and generate a signal to micro controller.

i have done using a comparator and the output of comparator is fed to micro controller as an interrupt.
This method is working for me only in no load condition.
When my unit is running in full load condition, my controller is not able to detect the interrupt,i mean the time is not sufficient.

That is why i am looking for a Battery switch over for my application.

Thanks and Regards,
Viswanath.

 

[millwood]

check your mcu to see if it has brown out detection - most do.

then you just need to read the datasheet.

 

[yviswanathbe]

Hi millwood,

I am using C8051F120 Microcontroller from Silabs.

My Controller has internal Brown Out Detection.

But when enabled it resets the controller if the condition is detected.

What i need is i need to detect the power fail condition and store the data in FLASH.

Regards,
Viswanath

 

[bobcat1]

Hi

You can use the LTC4412 IC from linear tech simple to use it will automatically switch between your backup battery and main power supply

You can also use the STATUS I/O (via a buffer) to have indication whether the current power source is battery or mains

All the best

Bobi

The microcontroller specialist

 

[insrusingh]

Hi,

My design requirment is
Vinput varies from 6V to 36V.
and some ics need backup voltage and few doesnot.
So,what i have done is i have taken a mosfet whose gate is having VGSth-0.7V and i have put a resistor divider on gate so that at minimum volatge of 6V input the Vgs becomes 0.7V and if input volatge goes below 6V then VGs is leass than 0.7V so Mosfet whose drain is connected to VCC3V3_BATT and source connected to VCC3V3 nets gets isolated and the ics not requiring backup does get volatge.
But what is happening is Mosfet is dropping 1.2V across drain and source so its not working.Msfet used is FDN337N.
Can you please let me know why this is hapenning and anyother way to implement it.

 

[sunny1986]

Hw can i purchase microcontroller c8051f120 in india

 

[yviswanathbe]

Hi Sunny,

Where are you from in INDIA?

You can purchase from FARNELL INDIA(Now named as ELEMENT14).But some what costly.
visit the following link

http://in.element14.com/jsp/search/results.jsp?N=0&Ntk=gensearch_001&Ntt=c8051f120&Ntx=mode+matchallpartial&suggestions=false&ref=globalsearch&_requestid=62672&isGoback=false&displaytext=&isRedirect=false

.

how much quantity you are looking for?
We have authorized distributors for SILBAS in Bangalore. But only problem is they support only for larger quantities(90 pcs).
If you want the contact details let me know>