battery charger

Posted by: Mara on 06/01/2012

Hello,
I want to built battery charger for LiFePO4.
I would like to have on output 11V and 16A, but the problem is that PI Expert only allow me to choose 11 V and maximum 12A. Can you tell me why can not i choose more current?

I have choosen TOPSwitch-HX, EN(eSIP-7C) package, 132Khz, open frame, secondary TL431.
Next page : single 230 V and in the follow page I have to choose output values so I have choosen 11V, but it did not allow me to choose 16A so I had to choose 12A.
Thank you for answers,

Marek Vrba

Comments

Hi

The flyback topology is not optimized for high current outputs, due to the extremely high peak secondary current, output current ripple. On top of that your PSU requires more than 180W, which may also be a problem for a single mosfet hard switching at 132kHz due to high switching losses (and potential EMI issues). Some of these disadvantages would be slightly smaller at high line applications only, but the heat dissipation, and EMI would still be big problems I believe

Typically you will also need some sort of Power Factor Correction (according to the standard EN61000-3-2), although you would have to confirm this yourself (it depends on the application). If that's the case then you will need a PFC stage. If you use a flyback together with a PFC that will bring your system efficiency further down.

I don't know your efficiency requirements, but I would probably recommend a HiperPFS + HiperTFS or HiperPFS + HiperLCS for your application. The Hiper PFS is used on the PFC stage, and the Hiper TFS integrates 3 Mosfets to do a two switch forward together with a standby power supply. The Hiper LCS integrates two Mosfets for a LLC converter.

There is a lot of information on the application notes of these families, and there is a section of the forum that is dedicated to high power designs here

PI Expert let me to do maximum 12A. So do you think this will be problem?
Or shoud I decrease more current value?
Thank you for answers.

That depends a lot on your objectives and requirements. 11V/12A may require PFC already which means you will still need a first stage.

As for the second stage, 12A is still going to be problematic, particularly if you do a single stage only with universal input voltage. If you do European input only, it will be more manageable. Still, you will have a considerable amount of ripple on the secondary side that will have to be handled by the output capacitors.