SHUTDOWN CIRCUIT FOR A SWITCHING REGULATOR IN A REMOTE CONTROLLED TELEVISION RECEIVER

摘要

In a switching regulator power supply (25), the primary winding (24a) of a switching transformer (24) is coupled to a source (21) of input voltage and to a power switch (Q1). Secondary supply voltages for a load circuit such as a television receiver are obtained from a secondary winding (24b) of the transformer (24). A regulator control circuit (30) develops a pulse width modulated signal that is used to control the duty-cycle of the power switch (Q1) for regulating the supply voltages. A disabling circuit (50) is coupled to the regulator control circuit (30) and is responsive to a low bias voltage at a disabling control terminal (61) to change the duty cycle of the power switch (Q1) in a manner that disables the normal transfer of energy to the load circuit. A disabling input terminal (A) is coupled to an input terminal (74) of a comparator (V3) and to the disabling control terminal (61). The comparator output is coupled to a disabling switch (Q37) having an output coupled to the disabling control terminal (61). A first signal generator (81) is responsive to a first condition requiring the disabling of the power supply and develops at the disabling input terminal (A) a first bias voltage that is low enough to, in turn, bias low the disabling control terminal (61) to initiate the disabling of the power supply. A second signal generator (29c) is responsive to a second condition requiring the disabling of the power supply and develops a second bias voltage that is higher than the first bias voltage and is high enough to activate the comparator (V3). When the comparator (V3) is activated, the disabling switch (Q37) turns on to bias low the disabling control terminal (61) to initiate the disabling of the power supply (25).