Power supply circuit
First Claim
1. A voltage booster type switching power supply circuit for boosting an input voltage supplied from a DC power source by means of PWM (Pulse Width Modulation) method so as to supply a predetermined output voltage to a load, comprising:
- a coil having one end thereof connected to one end of the DC power source;
a rectifying element connected between other end of the coil and one end of the load;
an output current detection resistor for detecting current flowing through the load;
an output capacitor, connected between a node at which the rectifying element and the load are connected together and ground, for producing the output voltage across both ends thereof by being electrically charged;
a switching element connected between the other end of the coil and ground;
a drive circuit for stabilizing the output voltage by controlling the switching element by means of PWM method in accordance with a voltage appearing across the output current detection resistor;
a start/stop circuit for regulating an amount of the output current by starting and stopping the drive circuit according to an external input signal fed externally thereto; and
a soft-start circuit for controlling the drive circuit so as to increase the output voltage gradually by becoming operative when the external input signal becomes active for the first time after startup, and controlling the drive circuit so as to increase the output voltage promptly by becoming inoperative when the external input signal becomes active for the second time and thereafter after startup.
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Accused Products
Abstract
The voltage booster type switching power supply circuit is provided with a drive circuit for controlling a switching element, a start/stop circuit for turning the drive circuit on and off according to a brightness control signal for adjusting a brightness of a light source of a liquid crystal display device, an output voltage detection circuit for detecting whether the output voltage is greater than a predetermined voltage and feeding out a result as a comparison result signal, and a soft-start circuit that does not operate when the comparison result signal is active on the rising edge of the brightness control signal, and that operates so as to increase the output voltage gradually when the comparison result signal is inactive on the rising edge of the brightness control signal.
78 Citations
12 Claims
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1. A voltage booster type switching power supply circuit for boosting an input voltage supplied from a DC power source by means of PWM (Pulse Width Modulation) method so as to supply a predetermined output voltage to a load, comprising:
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a coil having one end thereof connected to one end of the DC power source;
a rectifying element connected between other end of the coil and one end of the load;
an output current detection resistor for detecting current flowing through the load;
an output capacitor, connected between a node at which the rectifying element and the load are connected together and ground, for producing the output voltage across both ends thereof by being electrically charged;
a switching element connected between the other end of the coil and ground;
a drive circuit for stabilizing the output voltage by controlling the switching element by means of PWM method in accordance with a voltage appearing across the output current detection resistor;
a start/stop circuit for regulating an amount of the output current by starting and stopping the drive circuit according to an external input signal fed externally thereto; and
a soft-start circuit for controlling the drive circuit so as to increase the output voltage gradually by becoming operative when the external input signal becomes active for the first time after startup, and controlling the drive circuit so as to increase the output voltage promptly by becoming inoperative when the external input signal becomes active for the second time and thereafter after startup. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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Specification