Control of a resonant switching system with monitoring of the working current in an observation window

Abstract

Controlling a resonant switching system, which includes a first switch and a second switch in a half-bridge configuration for driving a resonant load. A corresponding control system includes command means for switching on and switching off the switches alternatively according to a working frequency of the switching system. The control system includes detection means for detecting a zeroing of a working current being supplied by the switching system to the resonant load in a temporal observation window; the observation window follows each switching off of at least one of the switches, and has a length equal to a fraction of a working period of the switching system. Correction means are then provided for modifying the working frequency in response to each detection of the zeroing in the observation window.

1 . A control system for a resonant switching system, the switching system including a first switch and a second switch in a half-bridge configuration for driving a resonant load, wherein the control system includes:
 command means for switching on and switching off the switches alternatively according to a working frequency of the switching system,   detection means for detecting a zeroing of a working current being supplied by the switching system to the resonant load in a temporal observation window, the observation window following each switching off of at least one of the switches and having a length equal to a fraction of a working period of the switching system, and   correction means for modifying the working frequency in response to each detection of the zeroing in the observation window.   
   
   
       2 . The control system according to  claim 1 , wherein the command means include means for alternatively applying a switching on signal and a switching off signal to each switch with a dead-time between the switching off signal of each switch and the switching on signal of the other switch, the observation window being at least equal to the dead-time. 
   
   
       3 . The control system according to  claim 1 , further including programming means for programming the length of the observation window. 
   
   
       4 . The control system according to  claim 3 , wherein the command means include an oscillator for generating a ramp-like oscillation signal, and means for operating the switching on and the switching off of the switches according to the oscillation signal, the programming means including means for defining the length of the observation window according to a comparison between the oscillation signal and a threshold value. 
   
   
       5 . The control system according to  claim 4 , wherein the programming means includes means for varying the threshold value. 
   
   
       6 . The control system according to  claim 3 , wherein the detection means includes measuring means for measuring a measuring quantity indicative of the working current at a measuring terminal of the control system, the programming means including offset means for applying an offset to the measuring quantity. 
   
   
       7 . The control system according to  claim 6 , wherein the measuring means includes a measuring resistor connected in series to the at least one switch for conducting the working current, and wherein the offset means includes a programming resistor connected between the measuring terminal and the measuring resistor and a current generator for applying a predefined current to the programming resistor, the measuring means measuring a voltage at the measuring terminal being defined by the sum of the voltage at the measuring resistor and the voltage at the programming resistor. 
   
   
       8 . The control system according to  claim 1 , wherein the correction means includes incrementing means for incrementing the working frequency by an amount corresponding to a difference between the detection of the zeroing and an end of the observation window. 
   
   
       9 . The control system according to  claim 8 , wherein the incrementing means includes means for incrementing the working frequency by a minimum amount in response to each detection of the zeroing in the observation window. 
   
   
       10 . The control system according to  claim 1 , further including:
 means for detecting a number of zeroing different from one between two consecutive observation windows, and   means for switching off the switches in response to each detection of the number of zeroing different from one.