Switched mode power supply including a flyback converter with primary side control

A SMPS circuit comprising:

• a transformer having a primary winding, a secondary winding, and an auxiliary winding, the primary winding operably carrying a primary current, the secondary winding operably carrying a secondary current, and the auxiliary winding operably providing a feedback voltage;
• a semiconductor switch coupled in series to the primary winding for switching the primary current on and off in accordance with a control signal;
• a current measurement circuit coupled to the semiconductor switch or the transformer for measuring the primary current;
• a diode coupled in series to the secondary winding for rectifying the secondary current;
• a controller configured to receive the feedback voltage, a reference signal, and the measured primary current and generate the control signal for the semiconductor switch dependent on the feedback voltage, the reference signal, and the measured primary current, wherein the semiconductor switch is switched on and off cyclically in CCM operation;
• and
• a compensation circuit configured to receive the reference signal;
• regularly interrupt operation of the semiconductor switch such that the secondary current drops to zero while the semiconductor switch is off;
• sample the feedback voltage at a first time instant to obtain a first sampled value, wherein the first time instant occurs when the secondary current reaches zero;
• resume the operation of a semiconductor switch;
• sample the feedback voltage at a second time instant to obtain a second sampled value, wherein the second time instant occurs when the control signal indicates to switch the semiconductor switch on;
• sample the measured primary current at a third time instant to obtain a third sampled value, wherein the third time instant occurs when the semiconductor switch has switched on;
• and adjust the reference signal dependent on the first, the second, and the third sampled values upstream of the controller.

An electronic controller device for controlling a flyback converter, the electronic controller device comprising:

• a transformer having a primary winding, a secondary winding, and an auxiliary winding, the primary winding operably carrying a primary current, the secondary winding operably carrying a secondary current, and the auxiliary winding operably providing a feedback voltage;
• a power semiconductor switch coupled in series to the primary winding for switching the primary current on and off in accordance with a control signal;
• a current measurement circuit coupled to the semiconductor switch or the transformer for measuring the primary current;
• a diode coupled in series to the secondary winding for rectifying the secondary current;
• a controller configured to receive the feedback voltage, a reference signal, and the measured primary current and generate the control signal for the semiconductor switch dependent on the feedback voltage, the reference signal, and the measured primary current, wherein the semiconductor switch is switched on and off cyclically in CCM operation;
• and
• a compensation circuit configured to receive the reference signal;
• regularly interrupt operation of the semiconductor switch such that the secondary current drops to zero while the semiconductor switch is off;
• sample the feedback voltage at a first time instant to obtain a first sampled value;
• resume the operation of the semiconductor switch;
• sample the feedback voltage at a second time instant to obtain a second sampled value;
• sample the measured primary current at a third time instant to obtain a third sampled value;
• and adjust the reference signal dependent on the first, the second, and the third sampled values upstream of the controller.

A method for controlling a flyback converter, the method comprising:

• interrupting operation of a semiconductor switch that is in series with a primary winding of a transformer of the flyback converter such that a secondary current flowing through a secondary winding of the transformer drops to zero while the semiconductor switch is off, wherein the interrupting occurs at regular intervals;
• sampling a feedback voltage at an auxiliary winding of the transformer at a first time instant to obtain a first sampled value, wherein the first time instant occurs near when the secondary current reaches zero;
• resuming the operation of a semiconductor switch;
• sampling the feedback voltage at a second time instant to obtain a second sampled value, wherein the second time instant occurs when a control signal indicates to switch the semiconductor switch on;
• sampling a primary current in the primary winding at a third time instant to obtain a third sampled value, wherein the third time instant occurs when the semiconductor switch has switched on;
• and
• adjusting a reference signal dependent on the first, the second, and the third sampled values.