Sgs-thomson Microelectronics S.a.

Jean-Marc Merval

Philippe Maige

Michel Imbert

Danika Perrin

In a switching power supply controlled by modulated width pulses obtained by comparison between a saw-tooth voltage (15) oscillating between first and second levels and a servo control voltage (19), the servo control voltage is initially set to a value external to the oscillation interval of the saw-tooth, then, in a first phase, varies up to a first level (dead time) and, in a second phase, varies from the first to the second level for supplying control pulses having progressively increasing widths. A circuit (45, 50) ensures the variation of the servo control voltage during the first phase according to a first slope and then the variation of said servo control voltage during the second phase according to a second slope, lower than the first one, and a circuit (60) causes the slope switching after the detection of the first control pulse.

Progressive start up device for a switching power supply

A detection circuit of a line synchronization signal in a video signal wherein the synchronization signal is sent to a phase locked loop (PLL) comprises a voltage controlled oscillator (8), for supplying a line scanning signal to a display. The following steps are provided: inhibiting the operation of the loop and setting the VCO to its free frequency, in the absence of the line synchronization signal; supplying a detection window in relation with the oscillations of the VCO; and detecting the presence of the synchronization signal in this window for supplying either an enabling signal after the detection of a determined number of synchronization tops, this enabling signal connecting again the VCO in the loop, or an inhibiting signal if the detection is interrupted during the determined number of synchronization tops.

Line synchronization detection circuit

A detection circuit for a video tape recorder signal on the input of a TV set connected to a line synchronization separating circuit (11) in turn connected to a PLL (12) comprises a first phase comparator (15), the PLL (12) exhibiting a first time constant (I1, C1) corresponding to an operation on a normal TV signal. This circuit further comprises a switch (20) for switching the PLL on a second time constant (3I1, C1) shorter than the first one, a second phase comparator (22) for comparing the input and output phases of the first phase comparator, the second phase comparator being associated with a third time constant (I2, C2) shorter than the first and second ones, a threshold comparator (24) supplying to the switch (20) a control signal when the comparator output (22) is outside determined limits.

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Saint Egreve, France

Jean-Marc Merval