Question

A 3.5 current source is connected to a 220 ohms load. The source resistance is 6kohms. Solve for the equivalent voltage source (E and Rs) for this practical source.

Answer 1

Practical Voltage Source

An ideal voltage source means a device that offer a terminal voltage which doesn’t depend on the current flow through it. But such ideal sources never exist practically. Suppose a battery would produce 12V when no load is connected or no current flows through it, then the battery produce a less voltage than 12V when a load current flows through it. These sources are called as practical voltage sources. However, as long as small power or currents drawn from the load, these practical sources represent the ideal voltage sources.Therefore, the real model of device (practical voltage source) is obtained by an ideal voltage source with a series resistor. This series resistor resembles the voltage drop in the device when the current flows through it. The series resistor is called as the internal resistance of the voltage source. This does not mean that we can find such arrangement inside every practical source device but merely represents the reduction in terminal voltage on an account for an increase of load current flow.

Practical Current Source

Similar to an ideal voltage source, an ideal current source also never exists as there is no device or source that delivers a constant current independent of connected load resistance or the voltage across the load terminals. However, if the load voltage is small, load current in practical current source and current from ideal current source are equal. Therefore, a real model or practical current source is obtained from an ideal current source in parallel with resistance (or internal resistance). This resembles , the current changes in a practical current source with change in voltage of the load (or change in resistance of the load).