Forward converter having a primary-side current sense circuit

A load control device for controlling the amount of power delivered to an electrical load, the load control device comprising:

• an isolated forward converter operable to receive a bus voltage and to conduct a load current through the electrical load, the forward converter comprising a transformer that comprises a primary winding coupled in series with a first semiconductor switch and a secondary winding adapted to be operatively coupled to the electrical load, the forward converter further comprising a sense resistor coupled in series with the primary winding for producing a sense voltage representative of a primary current conducted through the primary winding;
• a controller coupled to the forward converter for controlling the first semiconductor switch to control the magnitude of the load current conducted through the electrical load to control the amount of power delivered to the electrical load to a target amount of power;
• and
• a current sense circuit operable to receive the sense voltage and to average the sense voltage when the first semiconductor switch of the forward converter is conductive, so as to generate a load current control signal that is representative of a real component of the primary current;
• wherein the current sense circuit is operable to average the sense voltage for an on time when the first semiconductor switch of the forward converter is conductive plus an addition amount of time, so as to generate the load current control signal that is representative of the real component of the primary current.

An LED driver for controlling the intensity of an LED light source, the LED driver comprising:

• an isolated forward converter operable to receive a bus voltage and to conduct a load current through the LED light source, the forward converter comprising a transformer that comprises a primary winding and a secondary winding adapted to be operatively coupled to the LED light source, the forward converter further comprising a half-bridge inverter circuit for generating an inverter voltage that is coupled to the primary winding of the transformer through a capacitor for producing a primary voltage across the primary winding, the forward converter further comprising a sense resistor coupled in series with the primary winding for producing a sense voltage representative of a primary current conducted through the primary winding;
• a controller coupled to the forward converter for controlling the half-bridge inverter circuit to control the load current conducted through the LED light source to control the intensity of the LED light source to a target intensity;
• and
• a current sense circuit operable to receive the sense voltage and to average the sense voltage when the magnitude of the primary voltage across the primary winding is positive and greater than approximately zero volts, so as to generate a load current control signal that is representative of a real component of the primary current.

A forward converter for controlling the amount of power delivered to an electrical load from an input voltage, the forward converter comprising:

• a transformer comprising a primary winding and a secondary winding adapted to be operatively coupled to the electrical load;
• a half-bridge inverter circuit comprising first and second semiconductor switches coupled in series across the input voltage for generating an inverter voltage at a junction of the two semiconductor switches;
• a capacitor coupled between the junction of the two semiconductor switches of the half-bridge inverter circuit and the primary winding of the transformer, such that a primary voltage is produced across the primary winding, the transformer operable to transfer power to the secondary winding when either of the semiconductor switches is conductive;
• a controller coupled to the half-bridge inverter circuit for controlling the first and second semiconductor switches to control a load current conducted through the electrical load;
• a sense resistor coupled in series with the primary winding for producing a sense voltage representative of a primary current conducted through the primary winding;
• and
• a current sense circuit operable to receive the sense voltage and to average the sense voltage when the first semiconductor switch of the half-bridge inverter circuit is conductive, so as to generate a load current control signal that is representative of a real component of the primary current.