Electrical current is defined as the flow of electric charge. The flow of electric charge is often realized through the flow of electrons through a conducting medium. Electric current traveling through a conducting medium may be used to send data signals or provide power to various devices. It is often beneficial to measure the amount of electric current being consumed by a particular device. For example, monitoring the actual electric current consumed by a particular device may enable better control over energy efficiency and energy costs.
One way of measuring current is to place a small resistor along the path of the desired current signal to be measured. By measuring the voltage drop across the resistor, the amount of current may be determined through Ohm's law. Ohm's law indicates that the electric current measured in amperes is equal to the voltage drop measured in volts divided by the value of the resistor measured in ohms. Although this method may provide a relatively accurate measurement of the current, it unnecessarily consumes power. Electrical energy carried by the electric current is transferred to thermal energy through the resistor. Thus, measurement of electric current through a resistor is not energy efficient and may create excessive heat.
There are methods known in the art for measuring electric current without requiring an additional resistor to be added to the circuit. These methods may be referred to as “lossless.” One of these methods is to measure the voltage drop across the Direct Current Resistance (DCR) of the inductor which is part of a switched mode power supply. Again, through use of Ohm's law, the electric current can be determined by the voltage drop divided by the DCR of the inductor. However, the DCR of the inductor is not very accurate and drifts according to temperature changes. Thus, the accuracy of the current measured through this method is only as accurate as the value of the DCR resistance.
Another lossless measurement technique is to measure the voltage drop across the resistance (RDS) between the drain and the source terminals of a Metal-Oxide Semiconductor Field-Effect Transistor (MOSFET) device. However, the value of RDS is also very inaccurate and drifts even more in response to temperature changes.
Throughout the drawings, identical reference numbers designate similar, but not necessarily identical, elements.