A
dependent source is one in which the voltage or current of the source output is dependent on another voltage or current elsewhere in the circuit. There are thus four possible types: current-dependent voltage source, voltage-dependent voltage source, current-dependent current source, and voltage-dependent current source. Non-ideal dependent sources can be modelled with the addition of an impedance in the same way as non-dependent sources. These elements are widely used to model the function of
two-port networks; one generator is needed for each
port, and it is dependent on either voltage or current at the other port. The models are an example of
black box modelling; that is, they are quite unrelated to what is physically inside the device but correctly model the device's function. There are a number of these two-port models, differing only in the type of generator required to represent them. This kind of model is particularly useful for modelling the behaviour of transistors. The model used to represent
h-parameters is shown in the figure.
h-parameters are frequently used in transistor
data sheets to specify the device. The
h-parameters are defined as the matrix : \begin{bmatrix} V_1 \\ I_2 \end{bmatrix} = \begin{bmatrix} h_{11} & h_{12} \\ h_{21} & h_{22} \end{bmatrix} \begin{bmatrix} I_1 \\ V_2 \end{bmatrix} where the voltage and current variables are as shown in the figure. The circuit model using dependent generators is just an alternative way of representing this matrix. ==References==