81-6 Source transformations The ideal voltage source and a series resistance comprise a practical voltage source. RsE R --internal-resis tance R L R.+r R R L R+R A practical current source is defined as an ideal current source in parallel with an internal resistance r R.R L R+r L R Rail L R L R+R§1-6 source transformations The ideal voltage source and a series resistance comprise a practical voltage source. R int ernal resistance s − − − s L s L R R i + =   s L s L L L L R R R R i + = =    A practical current source is defined as an ideal current source in parallel with an internal resistance Rsi. s si L si L L i R R R R +  = s si L si L L L i R R R i R + = / = RL L i − +  L − +  s Rsv RL L i − +  L s i Rsi