Forward power converter controllers
This invention relates to control techniques and controllers for resonant discontinuous forward power converters (RDFCs). A method of controlling a resonant discontinuous forward converter (RDFC), said converter including a transformer with primary and secondary matched polarity windings and a switch to, in operation, cyclically switch DC power to said primary winding of said transformer, said converter further having a DC output coupled to said secondary winding of said converter, said method comprising: sensing a primary winding signal during an on period of said switch, said primary winding signal representing a current in said primary winding; comparing said sensed primary winding signal with a threshold value; and controlling one or both of an on and off duration of said switch in response to said comparison.
1. A method of detecting an overload condition of a resonant discontinuous forward converter (RDFC), said converter including a transformer with primary and secondary matched polarity windings and a switch to, in operation, cyclically switch DC power to said primary winding of said transformer, said converter further having a DC output coupled to said secondary winding of said converter, said method comprising:
sensing a primary winding signal during an on period of said switch, said primary winding signal representing an operational current in said primary winding;
comparing said sensed primary winding signal with an overload threshold; and
generating an overload signal for triggering an overload condition in said RDFC, said overload signal representing a period during which said sensed primary winding signal is greater than said overload threshold;
the method further comprising:
sensing a first event associated with switch on of said switch;
sensing a second event associated with said overload signal;
determining a duration between said first and second events;
comparing said duration with an overload period threshold value;
generating an early overload detection signal for detecting an early overload condition of said RDFC, said early overload detection signal being generated in response to said sensed duration being below said overload period threshold value.
2. A method according to claim 1 , wherein said duration is sampled over two or more on and off cycles of said switch and wherein said duration is compared with said overload period threshold value.
3. A method for regulating an output voltage of a resonant discontinuous forward converter (RDFC), said converter including a transformer with primary and secondary matched polarity windings and a switch to, in operation, cyclically switch DC power to said primary winding of said transformer, said converter further having a DC output coupled to said secondary winding of said converter, said method comprising:
sensing a primary winding signal during an on period of said switch, said primary winding signal representing an operational current in said primary winding;
comparing said sensed primary winding signal with a regulation threshold value; and
controlling one or both of an on and off duration of said switch in response to said comparison;
wherein said sensing of said primary winding signal comprises:
detecting turn on of said switch;
waiting for a delay period;
sampling said primary signal at an end of said delay period.
4. A method according to claim 3 , wherein said detecting turn on of said switch comprises:
detecting an increase in said primary winding signal following turn on of said switch that is greater than a first threshold.
5. A method according to claim 3 wherein said detecting turn on of said switch comprises:
detecting a drive signal of said switch.
6. A method according to claim 3 , wherein said detecting turn on of said switch comprises:
detecting a voltage across said switch.