Circuit and method for protecting a switching power supply from a fault condition

A switching regulator for generating a drive signal in response to a feedback signal, comprising:

• a timer circuit that monitors a level of the supply voltage for providing a timer period at an output when the supply voltage reaches a reference level;
• a detector circuit having a first input coupled for receiving the feedback signal and a second input coupled to the output of the timer circuit for receiving the timer period, wherein the detector circuit counts occurrences of the feedback signal during the timer period and generates a fault signal as a result of the detector circuit counting a number of occurrences of the feedback signal during the timer period;
• a gate driver having a first input coupled for receiving the drive signal, a second input coupled for receiving the fault signal, and an output for enabling and disabling the drive signal in response to the fault signal;
• a first latch having a first input coupled to a first output of the timer circuit;
• and
• a first logic gate having a first input coupled for receiving the feedback signal, a second input coupled to a second output of the timer circuit, a third input coupled to a first output of the first latch, and an output coupled to a second input of the first latch.

A method of detecting a fault condition in a switching regulator which operates in response to a feedback signal to provide a drive signal, comprising the steps of:

• applying a supply voltage to a node to provide operating power to the switching regulator;
• comparing the supply voltage with a reference voltage to establish a timer period when the supply voltage is equal to the reference voltage;
• counting a number of occurrences of the feedback signal;
• and
• detecting the fault condition as a result of counting less than a predetermined value of the number of occurrences of the feedback signal during the timer period.

A method of detecting a fault condition in a switching regulator, comprising the steps of:

• generating a drive signal in response to a feedback signal which is representative of an output voltage;
• charging a power supply terminal of the switching regulator to a first voltage level to start a timer period;
• discharging the power supply terminal to establish a duration of the timer period;
• resetting the timer period after counting a number of occurrences of the feedback signal;
• and
• detecting the fault condition if the number of occurrences of the feedback signal counted before the timer period is reset is less than a predetermined value.

A method of operating a regulator circuit, comprising the steps of:

• generating a drive signal in response to a feedback signal;
• discharging a power supply terminal of the regulator circuit from a first level to a second level to establish a period of time;
• and
• disabling the drive signal as a result of counting less than a predetermined number of feedback signals in the period of time.