Abstract:
A method and a relative control circuit for generating a control voltage (Vg) of a synchronous rectifying transistor (M1) with the desired anticipation time in a new and effective way are proposed. The anticipation time is continuously controlled with a closed-loop technique by comparing it with the duration of a reference pulse (Tw). The resulting error signal (Verr) is processed and provides the necessary correction to the MOSFET gate signal (Vg) in order to equalize the actual anticipation time to the duration of the reference pulse.
Abstract:
A circuit and method capable to digitally control and, in particular, to properly turn off one or two Mosfets used as rectifiers in switched mode power supply (SMPS) isolated topologies is disclosed. Basic circuit implementation of the presented technique is also introduced. The controller (10) has a fixed frequency square wave signal main clock input (CK), generically swinging from a low to a high value in two different time intervals. The controller (10) has one or two square wave outputs, (Out 1 , Out 2 ), swinging from low to high in phase or in opposite with respect to the clock signal (CK). The digital control method is able to generate an output signals timing to anticipate output transitions (Out 1 , Out 2 ) from high to low level with respect to the clock signal (CK) transitions. In the control scheme, one or two other secondary inputs (x 1 , x 2 ) set the amount of time anticipation of the respective transitions of the outputs (Out 1 , Out 2 ). In isolated SMPS topologies with the PWM controller located on the primary side, the clock signal is derived from the secondary output of the isolation transformer, while the outputs are meant to drive one or two mosfet gates. The method is able to provide the proper gate drive signals, solving all the known problems in controlling synchronous rectification.
Abstract:
A switched mode power supply comprising a first circuit (100) provided with a primary winding (101) of a transformer to which a pulse voltage is applied, at least one second circuit (24, 900, 1, 90) comprising at least one secondary winding (25, 71, 72, 3, 11, 12) of said transformer, at least one reactor (26, 73, 74, 10, 13, 14) provided with a magnetic core and which has a terminal connected to a terminal of said at least one secondary winding (25, 71, 72, 3, 11, 12), at least one filter (LC) provided with input and output terminals and a first diode (D2, D20) connected in parallel to the input terminals of the filter (LC) is shown. The other terminal of the at least one reactor (10, 13, 14) is connected to a terminal of said first diode (D20). The power supply comprises a second diode (D50) which has a terminal connected to the other terminal of the first diode (D20) and the other terminal connected to the other terminal of the at least one secondary winding (3, 11, 12) and a control circuit (4, 41) coupled to a output terminal of the filter (LC) and to the other terminal of said at least one secondary winding (3, 11, 12). The control circuit (4, 41) generates a current (Irl) able to reset said magnetic core of said at least one reactor (10, 13, 14).