Integrated start-up circuit with reduced power consumption
First Claim
1. An integrated start-up circuit comprising:
- a start-up capacitor, for providing a supply voltage for powering a control-circuit of the power supply, wherein said start-up capacitor is coupled to a supply voltage terminal of said control-circuit;
a first bleeding resistor, connected from a first AC input of a bridge rectifier to said start-up capacitor;
a second bleeding resistor, connected from a second AC input of said bridge rectifier to said start-up capacitor; and
an ON/OFF circuit, for controlling PWM operation, wherein said ON/OFF circuit will enable PWM operation whenever said supply voltage of said start-up capacitor exceeds a start-threshold voltage, and wherein said ON/OFF circuit will disable PWM operation after the supply voltage drops below a stop-threshold voltage.
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Abstract
A switching power supply control-circuit according to the present invention uses bleeding resistors to charge a start-up capacitor and discharge an EMI filter. No extra discharge device is needed to accelerate the discharge of the input capacitor, since the start-up capacitor is charged up by the AC input source. A latch circuit of the power supply can be quickly reset after the AC input source is shut off. After the control-circuit begins to operate, the auxiliary winding of the transformer will power the control-circuit. To further reduce power consumption, the auxiliary winding generates a bias voltage to enable line-voltage detection. This allows the power supply to perform line-voltage detection and startup, without having to connect resistors or transistors to the input capacitor.
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Citations
6 Claims
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1. An integrated start-up circuit comprising:
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a start-up capacitor, for providing a supply voltage for powering a control-circuit of the power supply, wherein said start-up capacitor is coupled to a supply voltage terminal of said control-circuit;
a first bleeding resistor, connected from a first AC input of a bridge rectifier to said start-up capacitor;
a second bleeding resistor, connected from a second AC input of said bridge rectifier to said start-up capacitor; and
an ON/OFF circuit, for controlling PWM operation, wherein said ON/OFF circuit will enable PWM operation whenever said supply voltage of said start-up capacitor exceeds a start-threshold voltage, and wherein said ON/OFF circuit will disable PWM operation after the supply voltage drops below a stop-threshold voltage. - View Dependent Claims (2, 3, 4, 5, 6)
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Specification