Adaptive control of power converters by switched capacitors filters

An analog adaptive controller of power converters based upon a switched capacitor programmable filter is described. The transfer function of the external feedback network is continuously updated by the readouts of the input variables. A rough discretization of the inputs is obtained by a small number of fast comparators that digitally program the filter by means of a look-up table. The analog output drives the error amplifier of the switching converter controller whether it is PWM or phase-shifted or resonant. The present paper refers to a DC/DC converter even though the application can be addressed to any kind of power converter. The possibility of including the circuit into IC controller drivers is open. The non-linear overall characteristics of the power cells often show large differences in the dynamic behaviour depending on the operating point when the variations of the inputs are very large. The possibility of different conduction modes makes the use of a single time-invariant feedback network extremely downgrading the frequency performances. This paper describes a possible circuit topology implementing the switched capacitor adaptive feedback as a second order external network whose transfer function, in the Z domain, can assume as many different forms as required. The potential of this solution is illustrated with a simple example concerning a PWM flyback converter spanning over the discontinuous and the continuous conduction modes. The difficult work of defining the feedback transfer functions set can be carried out by an automatic analysis and CAD tool. The control of large signal transients is also made possible.