BACKGROUND

A switch-mode power supply is an electronic circuit that converts an input direct current (DC) supply voltage into one or more DC output voltages that are higher or lower in magnitude than the input DC supply voltage. A switch-mode power supply that generates an output voltage lower than the input voltage is termed a buck or step-down converter. A switch-mode power supply that generates an output voltage higher than the input voltage is termed a boost or step-up converter.

Some switch-mode power supply topologies include a drive/power transistor coupled at a switch node to an energy storage inductor/transformer. Electrical energy is transferred through the energy storage inductor/transformer to a load by alternately opening and closing the switch as a function of a switching signal. The amount of electrical energy transferred to the load is a function of the ON/OFF duty cycle of the switch and the frequency of the switching signal. Switch-mode power supplies are widely used in electronic devices, particularly battery powered devices, such as portable cellular phones, laptop computers, and other electronic systems in which efficient use of power is desirable.

SUMMARY

A switch-mode power supply circuit that reduces undesirable effects of switching noise during circuit operation by blanking feedback voltage during transistor switching is disclosed herein. In one example, a switch-mode power supply circuit includes a feedback terminal, a control circuit, a comparator, and a switch. The comparator includes a first input terminal coupled to a reference voltage source, and an output terminal coupled to the control circuit. The switch includes a first terminal coupled to the feedback terminal, a second terminal coupled to a second input terminal of the comparator, and a third terminal coupled to the control circuit.

In another example, a switch-mode power supply circuit includes a feedback terminal, a comparator, a switch, and a control circuit. The feedback terminal is configured to receive a feedback signal. The comparator is configured to compare the feedback signal to a reference signal. The switch is coupled to the feedback terminal and the comparator, and is configured to pass the feedback signal from the feedback terminal to the comparator. The control circuit is coupled to the comparator, and is configured to generate a control signal that turns on a high-side transistor, to open the switch prior to an edge of the control signal, and close the switch subsequent to the edge of the control signal.

In a further example, a switch-mode power supply includes an inductor, a high-side transistor, a low-side transistor, a voltage divider, a control circuit, a comparator, and a switch. The high-side transistor, the low-side transistor, and the voltage divider are coupled to the inductor. The control circuit includes a first output terminal coupled to the high-side transistor, and a second output terminal coupled to the low-side transistor. The comparator includes a first input terminal coupled to a reference voltage source, and an output terminal coupled to an input terminal of the control circuit. The switch includes a first terminal coupled to the voltage divider, a second terminal coupled to a second input terminal of the comparator, and a third terminal coupled to a third output terminal of the control circuit.

In a yet further example, an electricity meter includes metering circuitry and a switch-mode power supply. The switch-mode power supply is coupled to the metering circuitry, and includes an inductor, a high-side transistor, a low-side transistor, a voltage divider, a control circuit, a comparator, and a switch. The high-side transistor, the low-side transistor, and the voltage divider are coupled to the inductor. The control circuit includes a first output terminal coupled to the high-side transistor, and a second output terminal coupled to the low-side transistor. The comparator includes a first input terminal coupled to a reference voltage source, and an output terminal coupled to an input terminal of the control circuit. The switch includes a first terminal coupled to the voltage divider, a second terminal coupled to a second input terminal of the comparator, and a third terminal coupled to a third output terminal of the control circuit.

