| 摘要 |
1. Switching supply unit regulated against input voltage and output power variations, of the type comprising a direct voltage source feeding in series a transformer primary (LP1 ), a switching transistor (T) and a measurement resistor (R0 ), a control circuit (41) allowing to supply recurring enabling pulses to the base of the switching transistor (T), a first transformer secondary (LP2 ) allowing to supply a first voltage (V2 ) for measurement of the value of the output voltage (Vs ) of the supply unit, means (Z) allowing to supply a second voltage (V0 ) of predetermined value, means (42) allowing to compare the first voltage (V2 ) and the second voltage (V0 ) and to deliver a reference voltage (Vr ) as a function of this comparison, means (43) allowing to determine the difference between this reference voltage (Vr ) and a measurement voltage (R0 IM ) appearing at the terminals of the measurement resistor (R0 ) when the transistor (T) is enabled, and to deliver a blocking signal for a determined value of this difference, and an interruptor (45) allowing to short-circuit the base of the switching transistor (T) under the action of this blocking signal to block the transistor again, characterized in that it further comprises means (LP3 , 46, 47) allowing to measure the conduction duration of the switching transistor (T or T1 ) and to modify the reference voltage (Vr ) as a function of this measurement for maintaining this duration constant from one cycle to another for each pair of determined values of input voltage and output power ; the device thus being adapted to pass from a complete transformer discharge mode to an incomplete transformer discharge mode maintaining a fixed operating frequency.
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