New 60A Mppt PV Charger Design

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Solar Mike

Joined: 08/02/2015
Location: New Zealand
Posts: 911
Posted: 09:59am 10 Feb 2021      

Whilst doing some research, came across some of the new design D2PAK-7 mosfets, they are very impressive, along with a better driver chip; so thought I might throw something together to give them a try out. I quite like the idea of not using a separate driver pcb module and using a bootstrap technique for the upper mosfet drive supply. The D2PAK mosfets allow a better layout over external TO247 types.

This latest design version 4.x uses a Silicon Labs Si823H4BB-IS1 isolated half bridge mosfet driver chip driving D2PAK - NTBGS4D1N15MC mosfets in a synchronous buck format; these ones are only 150v rated so PV voltage limited here.

The mosfets are soldered direct onto the top surface of the pcb, with heat conducted to the lower layer by a multitude of vias, the pcb them clamps via an heat conducting insulator to an alloy bar attached to the case side panel to conduct heat away. I have some 25mm x 25mm x 80mm alloy bars left over from an older project, so will put them to good use.

These type of mosfets have multi-source connection pins with short parallel internal links, resulting in very low lead inductance along with low RSon resistance; means I don't require multiple paralleled chips for high power output. The design has 3, one each for the PV-Battery isolation, buck converter and synchronous rectifier.

Here is the driver:

First cut of PCB 155 x 205mm:

As yet no schematic and no vias added on the pcb yet, just built on the fly, will do a schematic to pick up my errors.