# Dependent Current Source Explained

Dependent Current Source is a four terminal active circuit element whose output current is dependent on circuit current or voltage. An active circuit element is one which can deliver power to the circuit. In this article, we will discuss the concept of dependent current source in detail with the help of circuit diagram.

A current source is a circuit element capable of delivering constant current irrespective of the voltage across its terminal. This voltage across the terminals is imposed by the other circuit element.  This type of source is called independent current source. Independent and ideal source are same. However, in dependent current source, the output current is not constant but its value depends on the input circuit parameter viz. voltage or current. It is linearly related to input current or voltage. In fact, the output current is a scalar multiple of its input current or voltage.

Dependent Current Source is also known as controlled current source. This is because, the output is controlled by circuit current or voltage. It is denoted by a diamond in an electrical network. Though it is a four-terminal device, it is usually shown by two terminals. Typically, it is denoted as shown below. As discussed, the output of dependent current source depends on circuit current or voltage. Based on this, there are two types of dependent voltage source:

• Voltage Controlled Current Source (VCCS)
• Current Controlled Current Source (CCCS)

Voltage Controlled Current Source (VCCS):

It is defined as the source whose output current depends on the voltage across some circuit element. This output current is a scalar multiple of the input voltage. VCCS is denoted as shown below. The current Io is dependent on input voltage Vi. Output Io is k times the Vi. Here, “k” is a constant. The value of k = (Io / Vi). Thus, the unit of scaling factor k is ampere/volt. Ampere/ meter is also known as Mho and denoted by an inverted ohm sign i.e. “℧”. It is basically the admittance of the circuit when viewed from the output terminals of the VCCS.

Current Controlled Current Source (CCCS)

Current Controlled Current Source is defined as the electrical source whose output current is dependent on circuit current. Like VCCS, the output voltage of CCCS is a scalar multiple of input current. It is also a four terminal device with two input terminal and two output terminals. CCCS is shown below. It can be seen from the above diagram that, output voltage of CCCS is linearly related with the input current. In fact, this scaled by some constant α. “Io” (output) is α times the “i” (input current). This scaling factor α = (Io / i). Therefore, the scaling factor α is a dimensionless quantity.