# 7Ah,12V battery SMPS Charger Circuit using Buck or Flyback needed?

#### sprabhujh

Joined Mar 29, 2017
13
Hello Friends...! I want to make a SMPS Charger for 7Ah,12V battery using Buck Topology or Flyback topology. Help me out with some reference circuits or circuit diagrams.

#### Colin55

Joined Aug 27, 2015
519
What is the value of your supply voltage?

#### sprabhujh

Joined Mar 29, 2017
13
Hello Colin55, Thank you for your reply. I want to charge from 230Vac supply.I need circuit without using transformer.

#### crutschow

Joined Mar 14, 2008
28,536
You will need a switching isolation transformer, such as with a flyback design.

You might try the TI Webench designer.

How much battery charging current do you want?

#### Colin55

Joined Aug 27, 2015
519
Do you want to kill yourself, or electrocute your younger sister?

#### sprabhujh

Joined Mar 29, 2017
13
Hello Crutschow, isolation transformer is OK.but don't want to use transformer for AC side step down.

#### Colin55

Joined Aug 27, 2015
519
I want to kill someone with a bullet, but I don't want to use a gun.

#### sprabhujh

Joined Mar 29, 2017
13
I need charging current of 700 milli amps.

#### Colin55

Joined Aug 27, 2015
519
Get a 240v to 12v transformer at 1 amp This will produce AC Put 4 x 1 amp diodes on the two output wires in the form of a bridge. On the positive and negative of the bridge put an 8 ohm 3 watt or 5 watt resistor. Connect it up to the battery and put your fingers on the resistor. Let me know if you can hold it.

#### crutschow

Joined Mar 14, 2008
28,536
I need charging current of 700 milli amps.
.... isolation transformer is OK.but don't want to use transformer for AC side step down.
Look at the flyback designs in the Webench Designer for a max input voltage of 250Vac and an output of 12V and 0.7A.
You want the designs with output regulation via optoisolator such as the one below.
You will then likely need to add current limiting in the output or change the output regulation to current-mode instead of voltage-mode when charging the battery.