Method and apparatus for input charge control of a power supply

A controller for controlling a switch mode power supply having a switch, the controller comprising:

• a constant current control circuit having a first input to be coupled to receive an input current sense signal, a second input to be coupled to receive an input voltage sense signal, and a third input to be coupled to receive an output voltage sense signal and having an output coupled to provide a first control signal to control switching of the switch to regulate an output current of the power supply, the constant current control circuit including:
• an integrator coupled to the first input to receive the input current sense signal, wherein the integrator is coupled to generate a charge signal representative of a total charge received from an input of the power supply during a switching period of the switch by integrating the input current sense signal;
• an arithmetic operator circuit coupled to generate a product signal that is proportional to the input voltage sense signal multiplied by the charge signal;
• and
• a comparator coupled to the third input to receive the output voltage sense signal and coupled to the arithmetic operator circuit to receive the product signal, wherein the comparator is further coupled to compare the output voltage sense signal with the product signal and to determine a logic state of the first control signal in response, thereto.

A controller for controlling a switch of a power supply, the controller comprising:

• a first input to be coupled to receive an input current sense signal, a second input to be coupled to receive an input voltage sense signal, and a third input to be coupled to receive an output voltage sense signal;
• an output to provide a control signal to control switching of the switch to regulate an output current of the power supply;
• an integrator coupled to the first input to receive the input current sense signal, wherein the integrator is coupled to generate a charge signal representative of a total charge received from an input of the power supply during a switching period of the switch by integrating the input current sense signal;
• an arithmetic operator circuit coupled to generate a reference signal that is proportional to a ratio of the output voltage sense signal to the input voltage sense signal;
• and
• a comparator coupled to the integrator and the arithmetic operator circuit to compare the charge signal with the reference signal and to determine a logic state of the control signal in response, thereto.

A power supply, comprising:

• an energy transfer element to be coupled between an input voltage source and an output of the power supply;
• a switch coupled to the energy transfer element, wherein the switch switches between an ON state and an OFF state in response to a drive signal;
• and
• a controller coupled to the switch to control switching of the switch to regulate an output current of the power supply, wherein the controller includes:
• a first input to be coupled to receive an input current sense signal, a second input to be coupled to receive an input voltage sense signal, and a third input to be coupled to receive an output voltage sense signal;
• a constant current control circuit coupled to generate a first control signal in response to the input current sense signal, to the input voltage sense signal, and to the output voltage sense signal, wherein the constant current control circuit includes:
• an integrator coupled to the first input to receive the input current sense signal, wherein the integrator is coupled to generate a charge signal representative of a total charge received from an input of the power supply during a switching period of the switch by integrating the input current sense signal;
• an arithmetic operator circuit coupled to generate a product signal that is proportional to the input voltage sense signal multiplied by the charge signal;
• and
• a comparator coupled to the third input to receive the output voltage sense signal and to the arithmetic operator circuit to receive the product signal, wherein the comparator is further coupled to compare the output voltage sense signal with the product signal and to determine a logic state of the first control signal in response, thereto;
• and
• a logic circuit coupled to generate the drive signal in response to the first control signal.