Universal pulse width modulating power converter
First Claim
1. A power converter having a magnetic element and a switch for selectively interrupting a current through the magnetic element thereby forming an output voltage wherein a controller for the switch comprises:
- a. a control means coupled to the switch for controlling a duty cycle of the switch for regulating the output voltage; and
b. switching inhibiting means comprising a pulse skip circuit for generating a logic signal to inhibit switching of the switch when a difference between the output voltage and a desired level for the output voltage falls below a threshold and wherein the threshold is inversely related to a supply voltage.
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Abstract
A controller for a pulse width modulating (PWM) power converter. The controller monitors an output voltage and a current through a magnetic element for modulating a duty cycle of a main power switch. The controller is an eight-pin integrated circuit which controls either a forward converter or a post regulator without internal modifications. The monitored current of the forward converter forms a positive sensing signal. The monitored current of the post regulator forms a negative sensing signal. A current sense circuit of the controller forms an absolute value of either sensing signal. A soft-start circuit of the controller forms a start-up voltage ramp which is proportional to the level of a Vcc supply without requiring an external capacitor. A duty cycle of the main switch is gradually increased by comparing the start-up voltage ramp to the absolute value of the sensing signal. A pulse skipping circuit of the controller disables switching of the main switch under light load conditions. An error signal representative of a difference between the output voltage and a desired output voltage is compared to a pulse skip reference voltage. When the error signal falls below the reference voltage, the main switch is disabled. Because the pulse skip reference voltage is inversely related to the Vcc supply, pulsing of the main switch under light load conditions is spread out in time. A clock signal utilized to control switching of the main switch is generated internally or externally to the integrated circuit.
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Citations
8 Claims
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1. A power converter having a magnetic element and a switch for selectively interrupting a current through the magnetic element thereby forming an output voltage wherein a controller for the switch comprises:
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a. a control means coupled to the switch for controlling a duty cycle of the switch for regulating the output voltage; and
b. switching inhibiting means comprising a pulse skip circuit for generating a logic signal to inhibit switching of the switch when a difference between the output voltage and a desired level for the output voltage falls below a threshold and wherein the threshold is inversely related to a supply voltage. - View Dependent Claims (2, 3, 4)
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5. A power converter having a magnetic element and a switch for selectively interrupting a current through the magnetic element thereby forming an output voltage wherein a controller for the switch comprises:
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a. first sensor for sensing a current through the magnetic element;
b. second sensor for sensing the output voltage;
c. a switch control circuit coupled to the first sensor and to the second sensor for controlling a duty cycle of the switch based upon the current and the output voltage; and
d. switching inhibiting circuit comprising a pulse skip circuit for generating a logic signal to inhibit switching of the switch when a difference between the output voltage and a desired level for the output voltage falls below a threshold and wherein the threshold is inversely related to a supply voltage. - View Dependent Claims (6, 7, 8)
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Specification