Switched mode power converter and method of operating the same

Abstract

A switched mode power converter is disclosed, together with a method for operating the same. The power converter is adapted to be operable in the boundary conduction mode, and operation is interruptible in the absence of any load requirement.

Description

FIELD OF THE INVENTION[0001]This invention relates to switched mode power converters and a method of operating the same.BACKGROUND OF THE INVENTION[0002]The current to drive light emitting diodes (LED) for lighting and other applications is commonly provided by a switched mode power supply or other switched mode power converter. Moreover, a single switched mode power converter may be able to provide the current required for multiple LEDs or LED strings. In some applications it is desirable to be able to separately control or dim such individual LEDs or LED strings. It is well known to provide bypass switches in order to provide this control function. In circumstances when all the bypass switches connected to a switched mode power converter operating as an LED current generator are conducting, such that all the LEDs are off, it is feasible to also turn off the current generator in order to save power.[0003]The power savings that can be obtained by switching off a current generator fo...

AI Technical Summary

Benefits of technology

[0010]It is an object of the present invention to provide a switched mode power converter and method of operating the same which allows for high efficiency partial load operation.

[0017]Beneficially, the method may provide that the presence or absence of the requirement for the (i)th one of the plurality of LED loads is determined by a control signal PMW(i)_on, and the converter control signal corresponds to the logical combination AND of the PMW(i)_on control signals. Alternatively, the method may provide that the presence or absence of the requirement for the (i)th one of the plurality of LED loads is determined by a control signal PMW(i)_on, and the control signal corresponds to the logical combination NOT AND of the PMW(i)_on control signals. As further alternative, the method may provide that the presence or absence of the requirement for the (i)th one of the plurality of LED loads is determined by a control signal PMW(i)_off, and the converter control signal corresponds to the logical combination NOT OR of the PMW(i)_off control signals. As a yet further alternative, the method may provide that the presence or absence of the requirement for the (i)th one of the plurality of LED loads is determined by a control signal PMW(i)_off, and the control signal corresponds to the logical combination OR of the PMW(i)_off control signals. These four alternatives, in the first and third of which the converter control signal corresponds to a Conv_off signal, and in the second and fourth of which the converter control signal corresponds to a Conv_on signal, provide alternative, simple, methods of controlling the converter, without the requirement for complex circuitry.

[0020]Preferably the switched mode power converter comprises a smoothing capacitor. Since the inductor currents in such a switched mode power converter typically varies between zero and twice the required output current, a smoothing capacitor is particularly convenient for reducing the output ripple.

Problems solved by technology

Unfortunately, a current converter operated in CCM requires some time for the current to ramp up again; thus the current generator needs to turn on prior to the time when the bypass switch stops conducting.

Although it is possible to implement this, additional circuitry is required, which adds to the complexity and cost of the generator.

This, however, requires a relatively complex circuit, especially when the PWM inputs are not generated on chip.

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