Simple Wall Adapter to Battery Changeover Circuit

A Simple Wall Adapter to Battery Changeover Circuit is really important for systems that use battery power.

Its main job is to help switch smoothly between two different power sources usually a wall adapter as the main source and a battery as the backup.

This way the power supply to devices does not get interrupted.

The IC LTC4412 part is key in this process because it controls an external P channel MOSFET which acts like a perfect diode.

This allows for efficient power switching and sharing between the sources.

You can find these circuits in many important situations like emergency lights, portable gadgets and uninterruptible power supply (UPS) systems.

This article explores how an Wall Adapter to Battery Changeover Circuit works, how it is designed and how it is built using the LTC4412 integrated circuit.

Circuit Working:

Parts List:

The circuit diagram shown above highlights the key parts that make up the system.

At the center of this setup is the LTC4412 integrated circuit along with a P-channel MOSFET called FDN306P a Schottky diode named 1N5819 and a backup battery for emergencies.

When the wall adapter is plugged in and providing power the LTC4412 IC1 takes priority over other power sources.

To prevent any reverse current from flowing back into the adapter the Schottky diode D1 is very important.

At the same time the MOSFET Q1 turns on allowing power to flow straight from the adapter to the load.

During this time the backup battery stays disconnected from the circuit, which helps to keep its charge from running down.

If the wall adapter gets unplugged or stops working IC1 quickly switches the load to the backup battery ensuring that power continues to flow without any interruptions.

The status pin on the IC LTC4412 shows which power source is currently in use providing useful information for monitoring or control.

Additionally, a capacitor C1 is included in the design to help smooth out any voltage changes that might happen during the switching making the output voltage more stable.

Note: The wall adapter can take an input voltage ranging from 3 to 28 volts of direct current.

Meanwhile, the battery voltage can vary from 2.5 volts up to 28 volts.

Formulas with Calculations:

For designing a Simple Wall Adapter to Battery Changeover Circuit follow the below mentioned formulas with calculations:

Drain-to-Source Voltage (V_DS)

The MOSFETs maximum drain to source voltage rating must exceed the input voltage:

V_DS > V_input

On-Resistance (R_DS(on)

The MOSFET should have a low on-resistance to minimize power loss:

P_loss = I_load² * R_DS(on)

Drain Current (I_D):

The MOSFETs drain current rating must exceed the maximum load current:

I_D > I_load

where,

• V_DS is the drain to source voltage rating must exceed the input voltage of 12V
• R_DS(on) is Low on resistance minimizes power loss
• I_D is the Drain current must exceed the load current.

Capacitance Calculation:

The smoothing capacitor C1 stabilizes the output voltage:

C = (I_load * Δt) / ΔV

where,

• I_load is the load current in amperes
• Δt is the switching time in seconds
• ΔV is Allowed voltage ripple in volts

Example:

For I_load = 1A, Δt = 1ms, ΔV = 0.1V:

C = (1 * 0.001) / 0.1 = 0.01 F = 10,000 µF.

Note: In this circuit, a 22µF capacitor is sufficient due to the low load current and the LTC4412s fast response.

How to Build:

To build a Simple Wall Adapter to Battery Changeover Circuit follow the below mentioned steps for connections:

• Gather all the components as mentioned in the above circuit diagram.
• Connect pin 1 of IC1 to the drain pin of MOSFET Q1.
• Connect pin 2 and pin 3 of IC1 to GND.
• Connect pin 5 of IC1 to gate pin of MOSFET Q1.
• Connect pin 6 of IC1 to source pin of MOSFET Q1.
• Connect a source pin of MOSFET Q1 positive of to load and negative of GND.
• Connect a positive of capacitor C1 to source pin of MOSFET Q1
• Connect the cathode of diode D1 between positive of Capacitor C1 and source pin of MOSFET, and the anode of diode D1 to positive of wall adapter input DC.
• And the negative of wall adapter input DC to GND.

Conclusion:

This Simple Wall Adapter to Battery Changeover Circuit keeps the power flowing without any breaks by smoothly changing from a wall adapter to a battery.

The IC LTC4412 chip makes it easier to design which helps it work well and be dependable.

This circuit is perfect for low power uses that need strong backup power management.

References:

Alternative to LTC4412