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H-Bridge Battery Charging Concept

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samson.bunty1986

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Dear All,

Can anyone help me to know H-bridge charging.Can we charge a battery using H-bridge??

Thnaks in Advance
 

Yes you can, if you are sure that the battery is fully floating from the circuit driving the H-bridge (so you cannot connect battery ground to circuit ground). For a more detailled answer you need to provide more info.
 

Why would you ever want to drive a battery with a bidirectional driver like a H bridge? Sounds like all risk and no gain to me.
 

mtwieg said:
Why would you ever want to drive a battery with a bidirectional driver like a H bridge? Sounds like all risk and no gain to me.
Click to expand...

It's very common in backup power supplies like UPS-es (usually in sine wave inverters). It's done so that the same MOSFET bridge can be used for converting from DC-AC (via a bulky iron transformer) and also battery charging at the same time (the transformer winding is always connected to the bridge). That is the gain in using it.

While it is inefficient due to losses, the main purpose of using it is to keep parts count and circuit complexity down.

Hope this helps.
Tahmid.
 
Can you explain how the mosfet rectification works?? I have gone through so many sites. there i have seen like the drop is very less compare to conventional rectifier(Diodes) . Can anyone briefly expalin the operating modes?? How the body diodes works here??

---------- Post added at 12:15 ---------- Previous post was at 12:12 ----------

Hi WimRFP,

The mosfet H-bridge circuit used for bidirectional as inverter in battery mode and as charger in mains mode. But am not clear how the mosfets rectifyuing the AC and controlling the charging current. Kindly explain about this.
 

The drop is less than conventional rectifiers when the MOSFET is being used for synchronous rectification. When the body diode is being used, the drop may actually be higher. For the "ubiquitous" IRFZ44N, the forward voltage of the body diode is 1.3V.

Hope this helps.
Tahmid.
 

In mosfet rectifier we will be using Body diodes right(Freewheeling)?? So, the drop will be more..but how can people are saying that drop will be less if we use mosfet rectifer??
 


Tahmid brother, thanks a lot for your comments.. It also helped me. But one question. How to power the comparator that gives FET the controlling signal. Is another diode rectifier with regulator is used in this case?
 

Hi all,

Can anyone explain how the battery is charged using 4 mosfets?? how they are controlling the current if the battery is getting full. What are the driving ics used to drive the mosfets??

One more query, as we know mosfets are voltage control device. but how can they control current in charging mechanism??
 

Hello Samson,I a case of mosfet as we all know is a Voltage control component but normally to control the charging current you have to control the duty cycle of the gate signal since during charging mode the low side mosfet oscillate.
 

Hi Kabiru,

Thanks for your reply.

So ,you are saying that in charging mode the bottom two mosfets will be ON and Upper two mosfets will be OFF ..is it?? So how will be the flow of current to the battery and how the mosfets rectify the AC Voltage.

Thanks in advance

---------- Post added at 15:02 ---------- Previous post was at 14:57 ----------

What are the mosfets used in battery charging? I have gone through web and found that they will be using two N-channel and two P-channel mosfets.. Is it correct?? how they will be connected for charging??
 

Usually all N-channel MOSFETs are used. This is because, the same H-bridge is used for inverter. The upper 2 MOSFETs are driven by the high side drivers. But during charging this does not matter, since the upper 2 MOSFETs are off. The lower 2 MOSFETs are driven at different duty cycles according to the current required. They, along with the transformer winding, form a boost circuit and the duty cycle of the driving signal controls the output voltage to the battery and thus the current.

For driving the lower 2 MOSFETs, normal low-side drivers can be used.

Hope this helps.
Tahmid.
 
Dear Tahmid,

Thanks for your reply..

Can you explain how can they control the current using mosfets???

In charging mode lower 2 mosfets will be ON??? Tahmid ,please let me know how this charging done if upper mosfets are in OFF condition..I mean how the circuit gets closed loop??
 

samson.bunty1986 said:
Dear Tahmid,

Thanks for your reply..

Can you explain how can they control the current using mosfets???

In charging mode lower 2 mosfets will be ON??? Tahmid ,please let me know how this charging done if upper mosfets are in OFF condition..I mean how the circuit gets closed loop??
Click to expand...

The lower 2 MOSFETs make a boost circuit along with the transformer. The transformer is shorted and the current passes through the MOSFETs for the closed loop, when lower MOSFETs are on, storing energy in the transformer. When lower MOSFETs are off, this stored energy is released and passes through the body diode of the upper MOSFETs, through the battery to ground.

Hope this helps.
Tahmid.
 
Tahmid,

Thanks for your reply..

I have a query..Please don't mind if it is silly..

From the transformer,AC signal will come..Positive and negative.. At starting, Positive pulse will be connected to drain of lower left mosfet and negative is connected to Drain of lower right mosfet...How can negative pulse go from drian to source??

And when lower mosfets OFF,you said that stored energy released and passes through body diodes of Upper mosfets..How can a negative pulse trigger the body diode?? Kindly explain about this??

Am little confused..

Thanks in advance

---------- Post added at 10:41 ---------- Previous post was at 10:34 ----------

If mosfets ON, they are shorted along with transformer??? When the mosfets OFF the stored energy(Current) is released through body diodes of upper mosfets?? Then where we are controlling the current and Rectifying the AC ??

Kindly help me out to understand abt this..
 

samson.bunty1986 said:
If mosfets ON, they are shorted along with transformer??? When the mosfets OFF the stored energy(Current) is released through body diodes of upper mosfets?? Then where we are controlling the current and Rectifying the AC ??

Kindly help me out to understand abt this..
Click to expand...

We are controlling the current by controlling the amount of time for which transformer is shorted - thus controlling the amount of energy stored. By adjusting the amount of energy stored, we adjust the amount of energy released and thus charging current to the battery.

Hope this helps.
Tahmid.
 
Tahmid said:
We are controlling the current by controlling the amount of time for which transformer is shorted - thus controlling the amount of energy stored. By adjusting the amount of energy stored, we adjust the amount of energy released and thus charging current to the battery.

Hope this helps.
Tahmid.
Click to expand...

How can we calculate, how much current we gain when we shorted the transformer??How much amount of energy stored and how much current can we get?? Kindly send me any calculations how to calculate the current from the stored energy.. How to vary the pulse?? Will it be depends on battery reference voltage??

Thanks in advance
 

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