A power supply fault protection circuit.

摘要

A MOSFET power switch (Q1) in a DC-to-DC converter of a television apparatus has a drain electrode (D) that is coupled via a primary winding (T1A) of a chopper transformer (T1) to an input supply voltage (B+). A first signal (VG) at a given frequency causes, during normal operation, alternate conduction and nonconduction in the transistor (Q1). A second signal (VQ2) is generated that is proportional to the voltage developed across the internal "on" resistance of the transistor (Q1) when the transistor is conductive. The second signal (VQ2) is clamped when the MOSFET (Q1) is nonconductive. The second signal (VQ2) is coupled via a current sensing arrangement (51) to the transistor gate (G). The second signal (VQ2) prevents the transistor (Q1) from further conducting when the amplitude of the second signal (VQ2) exceeds a predetermined value that corresponds with a predetermined limiting threshold level of current (i1) in the transistor (Q1).