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Lead Acid Battery Charger: Size Reduction

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abhinand rd

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I am going to design a battery charger for lead acid batteries of 48V and around 40A(around 2kW).
the circuit consists of diode bridge rectifier, followed by booster PFC and then a full bridge converter.
although I have tested these converters operating at less than 100kHz. The magnetic components (Inductor and transformer) were designed around these frequencies.
Now I want to reduce the size of the charger. I want to go upto MHz operation in order to reduce the size of the magnetic components , thereby reducing the size of overall charger(increasing power by weight ratio). I would like to know what are the problems I need to address if I go for Mhz operation? or for starters is it even really possible to go Mhz operation without increasing losses significantly. Also at MHz operation , What about the EMI problems? what will be the necessary design to take care for EMI at this frequency? All I want to do is to reduce the size of the charger.. Kindly provide me some inputs regarding this. Thanking you in anticipation. :)
 

schmitt trigger

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At those power levels operating at Mhz operation you will require a soft switching converter (also known as ZVS or ZCS converters). Google the term.
Your PW board will have to be at least a 4-layer board, with all-surface mount components.
Lastly, thermal management in small, dense converters is a significant portion of the design challenge.
 

abhinand rd

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At those power levels operating at Mhz operation you will require a soft switching converter (also known as ZVS or ZCS converters). Google the term.
Your PW board will have to be at least a 4-layer board, with all-surface mount components.
Lastly, thermal management in small, dense converters is a significant portion of the design challenge.


Thank you for your kind reply. Can u please elaborate? I have near zero knowledge when it comes to PCB design. I am trying to learn. why the necessity to have atleast 4-layer board with all surface mount components? Can u please point out the exact problem that I would face if the design involves small, dense converters?
 

schmitt trigger

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"I have near zero knowledge when it comes to PCB design."

On a high performance converter, the PCB design is one of the top-three most important design considerations.

On a ZVS circuit, the parasitic elements work for you, not against you. But you have to keep them under control. A four layer board, with its dedicated power and ground planes, provides low impedance current paths for all of the circulating currents. That not only helps efficiency and overstressing the components, but reduces EMI as well.

Additionally, all that copper is an integral part of thermal management.

Surface mount components allow for the shortest possible current paths, and also avoid drilling too many holes in the power and ground planes. True, there will be vias to connect the top and bottom planes, but with good judgment and forethought, one can arrange the layout to minimize those.
 

mtwieg

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A phase shifted full bridge is already a ZVS converter, if designed properly. The PFC stage is the greater challenge, since it is very challenging to make a PFC that soft switches over a wide load/line range. You will probably be better off using an interleaved PFC to reduce size. Interleaving allows you to substantially decrease the DC link capacitor size, not just the inductor size.
 
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