초록 ▼

When a main switching transistor of a zero voltage switching power supply is conductive, a voltage is developed in a current sensing resistor coupled in series with the transistor. The voltage in the current sensing resistor is coupled to a first input of a comparator of the control circuit. A secon

When a main switching transistor of a zero voltage switching power supply is conductive, a voltage is developed in a current sensing resistor coupled in series with the transistor. The voltage in the current sensing resistor is coupled to a first input of a comparator of the control circuit. A second input of the comparator is coupled to a capacitor that develops a voltage that varies in accordance with an output voltage of the power supply. During a given conduction interval of the transistor, the comparator is triggered in accordance with the difference between the current sensing resistor voltage and the capacitor voltage. An output of the comparator is coupled to the base of the transistor for controlling the turn off instant of the transistor on a current pulse-by-current pulse basis. Under overload condition, when the transistor is turned off, a reverse collector current flows through the base-collector junction of the transistor. The reverse collector current produces a voltage in the current sensing resistor that is at opposite polarity with respect to the voltage there, during forward conduction of the transistor. The voltage produced by the sensed reverse current turns on a diode switch and charges the capacitor that is coupled to the comparator of the control circuit in a manner to reduce the peak forward collector current. Thereby, the peak forward current in the transistor decreases relative to a value that would have occurred without the protection.

대표청구항 ▼

[What is claimed is:] [1.]a supply inductance coupled to a source of an input supply voltage and to a switching transistor for producing current pulses in said inductance that are coupled to an output of said power supply, a given current pulse having a first portion at a first polarity, that flows

[What is claimed is:] [1.]a supply inductance coupled to a source of an input supply voltage and to a switching transistor for producing current pulses in said inductance that are coupled to an output of said power supply, a given current pulse having a first portion at a first polarity, that flows in said transistor, during a first portion of a cycle, when forward conduction occurs in said transistor, and a second portion, at an opposite polarity, during a second portion of said cycle, after said forward conduction ceases in said transistor;a source of a first control signal having a value that is indicative of a current limit;a control circuit coupled to said transistor and responsive to said first portion of said given current pulse and to said first control signal for limiting amplitudes of said current pulses, in a current mode on a current pulse-by-current pulse control basis, in accordance with said current limit value; anda protection circuit coupled to said control circuit and responsive to said second portion of said current pulse for varying said first control signal, in accordance with said second portion of said current pulse, to vary said current limit value, when a magnitude of said second portion is within a first range of values, the variation of said first control signal being disabled, when said magnitude of said second portion is within a second range of values.