Regulating output current from a primary side power converter by clamping an error signal

A method comprising:

• (a) receiving a feedback signal indicative of a first time, wherein an inductor current flowing through a primary inductor of a flyback converter stops increasing at the first time, and wherein the flyback converter outputs a current;
• (b) receiving a switch signal indicative of a ramp-up rate at which the inductor current increases;
• (c) generating a timing signal that indicates a target time at which the inductor current would reach a predetermined current limit if the inductor current continued to increase at the ramp-up rate;
• (d) generating an inductor switch control signal that has a pulse width, wherein the inductor switch control signal is generated using an output voltage of a pulse-width-modulation error amplifier;
• (e) generating a clamp signal using the timing signal;
• and
• (f) adjusting the pulse width of the inductor switch control signal using the clamp signal so as to limit the current output of the flyback converter.

A device comprising:

• an inductor switch that is controlled by an inductor switch control signal, wherein the inductor switch control signal has a pulse width;
• an inductor, wherein an inductor current flowing through the inductor increases at a ramp-up rate during a ramp time, wherein the ramp time ends at a first time, and wherein the inductor current stops increasing at the first time;
• a comparing circuit that generates a timing signal, wherein the timing signal indicates a target time at which the inductor current would reach a predetermined current limit if the inductor current continued to increase at the ramp-up rate;
• and
• a clamp generator circuit that generates a clamp signal, wherein the clamp signal has a voltage that depends on the timing signal, wherein the device outputs a current, and wherein the device uses the clamp signal to adjust the pulse width of the inductor switch control signal so as to limit the current output by the device.

A power converter that outputs an output current, comprising:

• a primary winding;
• a switch, wherein an inductor current flows through the primary winding when the switch is on and increases at a ramp-up rate, and wherein the switch is controlled by an inductor switch control signal;
• an error amplifier that outputs a voltage, wherein the inductor switch control signal has a pulse width, and wherein the pulse width of the inductor switch control signal is dependent on the voltage output by the error amplifier;
• and
• means for limiting the output current of the power converter in a constant-current mode by clamping the voltage output by the error amplifier, wherein the means clamps the voltage output by the error amplifier using a timing signal that indicates a target time at which the inductor current would reach a predetermined current limit if the inductor current continued to increase at the ramp-up rate.