function Get-FTPFile ($Source, $Target, $UserName, $Password) {

    # Create a FTPWebRequest object to handle the connection to the ftp server
    $ftprequest = [System.Net.FtpWebRequest]::create($Source)

    # set the request's network credentials for an authenticated connection
    $ftprequest.Credentials =
    New-Object System.Net.NetworkCredential($username, $password)

    $ftprequest.Method = [System.Net.WebRequestMethods+Ftp]::DownloadFile
    $ftprequest.UseBinary = $true
    $ftprequest.KeepAlive = $false

    # send the ftp request to the server
    $ftpresponse = $ftprequest.GetResponse()

    # get a download stream from the server response
    $responsestream = $ftpresponse.GetResponseStream()

    # create the target file on the local system and the download buffer
    $targetfile = New-Object IO.FileStream ($Target, [IO.FileMode]::Create)
    [byte[]]$readbuffer = New-Object byte[] 1024

    # loop through the download stream and send the data to the target file
    do {
        $readlength = $responsestream.Read($readbuffer, 0, 1024)
        $targetfile.Write($readbuffer, 0, $readlength)
    }
    while ($readlength -ne 0)

    $targetfile.close()
}

$sourceuri = "ftp://MyFtpServer/FolderPath\File.txt"
$targetpath = "C:\temp\MyFile.txt"
$user = "Username"
$pass = "Password"
Get-FTPFile $sourceuri $targetpath $user $pass