Sources of electrical energy whose value is controlled by either a current or voltage located elsewhere in the circuit. An example of a dependent source is the hi-fi amplifier, in which the output voltage is dependent on the input voltage to the amplifier. The symbols shown in the diagram show the four basic types of dependent source.

Types of dependent sources

• • The voltage-controlled voltage source (VCVS), sometimes called a voltage amplifier, senses an input voltage and produces an output voltage that is related to it by the gain factor K.

• • The current-controlled current source (CCCS), sometimes called a current amplifier, produces an output current that is related to the current flowing in its input by the gain factor K.

• • The voltage-controlled current source (VCCS), also known as an operational transconductance amplifier (OTA) or transconductance amplifier, senses an input voltage and produces an output current that is related to it by the constant g_m, which has the dimensions of conductance. The constant g_m is known as the transconductance of the amplifier.

• • The current-controlled voltage source (CCVS), or transresistance amplifier, produces an output voltage that is related to the current flowing in its input by the constant r_m, which has the dimensions of resistance.