DC-DC Converter(六)----同步整流管
Power Switch断开的瞬间,二极管闭合导通,所以在二极管上损耗的功率为:
当电流非常大时,损耗的功率也是相当可观的,常见的方法是换上低压差的二极管,例如肖特基。
更好的方法是使用MOSFET管。
这就是同步整流管,synchronous rectifier。
不过这又引入了另一个问题:两个开关有同时关闭的可能,这种现象称为shootthrough。
为了避免这种情况,一个简单的改良方法是在同步整流管上并联一个二极管:
当然这还不是最优的。
更精细的做法是监控两个开关交叉点处的电压,这称为 non-overlap protection。
“the voltage at the switch node (the point where S1, S2 and L are joined) is sensed to determine its state. When the switch node voltage passes a preset threshold, the time delay is started. The driver can thus adjust to many types of switches without the excessive power loss this flexibility would cause with a fixed non-overlap time.”
还有非常有趣的方法,就是VRM(Voltage Regulator Module)中常用的分相的方法。
基本思想是把Ton时间等分成n个小时隙。
“Each of the n "phases" is turned on at equally spaced intervals over the switching period.”
posted on 2012-11-19 23:55 freshair_cn 阅读(948) 评论(0) 编辑 收藏 举报