Design Battery Charger using H-bridge Mosfet concept

What's the battery technology? What is the vendor's charging recommendation? What other design requirements have you not yet disclosed?

If it's lead acid, why not just get a golf-cart charger? You can't possibly build one (with unit pricing at retail) for less cost...given your level of experience.

Why use H bridge when a single mosfet with PWM will do the job ?

What powers your battery charger?

Almost certainly not, but maybe. What battery type?

It can be two of each, or four N-channels. If you're charging from a direct-current source then you only need two MOSFETs.

You really, really, don't know enough to even start designing this. Normally you'd build a switching supply. You'd monitor the battery current and voltage, and control the charging current and/or voltage by modulating the duty cycle of the switching.

That depends on what you're doing. In a switching supply they are being rapidly turned on and off. The duration they're on vs. the total cycle time (the "duty cycle"), the supply voltage, and the load voltage all determine current.

In general they don't. If you're building an off-line switcher you generally rectify the incoming AC to DC, then use the resulting DC to power your electronics.

From the sounds of things you really need to learn more about electronics before you start trying to figure out a reference design.

The 2008 ARRL Handbook has a project for a 13.8V off-line switcher; many of the principles are the same as for your battery charger (in fact, there's a good chance that with the proper control electronics that circuit could be used to charge 12V lead-acid batteries).

I would suggest that you get onto the various semiconductor web sites and look for applications notes. "Off line power supply", "switching power supply" and "power factor correction" are all search terms that may get you useful applications notes.

If it's lead acid and you do build the charger, then you can't just go constant current -- you need to do a constant current charge up to a specific voltage (the nominal value of which escapes me at the moment, it varies with temperature, and I'm not sure that it doesn't vary by specific battery type).

--
Tim Wescott 
Control system and signal processing consulting 
www.wescottdesign.com

Charging a battery from a full-H bridge makes about as much sense as using a full-H bridge for motor _speed_ control, when it only should be used to change direction >:-} ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| Phoenix, Arizona  85048    Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
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I love to cook with wine.     Sometimes I even put it in the food.

Really?

I can think of a scenario..

Polarity auto sense and the ability to perform load testing between the charge pulse to test the life of the cell/battery.

Btw, we have a charger at work that does that very thing, it has a H bridge circuit. you can plop the battery on the holder any way you wish, it auto senses polarity and knows which side of the bridge to charge it on and uses the opposite side as a pulsed load test as it is being charged.

Jamie

So, it's fool proof because you only have fools to use it.

Hey! I resemble that remark!

--
My liberal friends think I'm a conservative kook. 
My conservative friends think I'm a liberal kook. 
Why am I not happy that they have found common ground? 

Tim Wescott, Communications, Control, Circuits & Software 
http://www.wescottdesign.com

Or controlled braking.

--
"For a successful technology, reality must take precedence  
over public relations, for nature cannot be fooled." 
                                       (Richard Feynman)

Yep. ...Jim Thompson

-- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at

| 1962 | I love to cook with wine. Sometimes I even put it in the food.

Guess no one has never heard of auto sensing polarity chargers and load testing.

We have a charger at work that uses an H bridge, you can connect the battery any way you wish, as long as it has at least .5 volt or more, anything less, it assumes nothing connected and does not make an attempt to select a polarity and turn on.

during a low state battery, the unit switches the bridge for a load test to determine if the battery is accumulating useful energy, if not, it'll give up and flash a bad battery LED>

Jamie