The present invention relates generally to power switching devices. More particularly, the present invention relates to a current sensing solution for power switching devices which reduces power losses and parasitic inductance without correspondingly occupying excessive space in a power supply.
High efficiency is one of the important parameters in designs for modern power supplies, and power density has increased accordingly. A feedback (sensed) current signal is another important factor in proper operation of the power conversion circuit.
One conventional example is represented in FIG. 1 of a current sensing circuit 10 for a power conversion circuit implementing MOSFET devices 11 (having gate 12, drain 13 and source terminals 14), wherein the current signal is obtained from opposing ends 15, 16 of a current sensing resistor.
Another conventional example of a current sensing circuit 20 as represented in FIGS. 2a and 2b may include a discrete current sense transformer 21 having a primary winding coupled to the drain terminal of a MOSFET switching device 11 and a secondary winding to which current sensing leads 15, 16 are coupled.
One of skill in the art may appreciate that each of the two aforementioned examples contribute to additional losses due to the copper winding/track and soldering joint, and also introduction of parasitic inductance due to additional copper track. Such losses arise in the context of power switching devices implementing either fully controllable power switching (e.g., three terminal devices such as a MOSFET), or uncontrollable power switching (e.g., two terminal devices such as a power diode).
Yet another problem which arises in such conventional arrangements is undesirable occupation of physical space, particularly with respect to the discrete transformer, whether with respect, for example, to horizontal surface area on a printed circuit board or vertical cross-section in a stacked arrangement.