function banner_obj(){
    
    var pos=1;
    
    this.change_ban=function(){
        (pos==1)?pos=2:pos=1;
        document.getElementById('banner_global').src='/img/global'+pos+'.png';
        window.clearTimeout(mb_timer);
        mb_timer=window.setTimeout(function(){m_banner.change_ban();},3000);
    }
    
}

var m_banner=new banner_obj();
var mb_timer=window.setTimeout(function(){m_banner.change_ban();},3000);