US 2008/0164828 A1Published application

Electronic circuit for driving a diode load

AssigneeAllegro MicroSystems, LLC

InventorsGregory Szczeszynski, Shashank Wekhande, Vijay Mangtani

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Abstract

An electronic circuit includes circuit portions for identifying a largest voltage drop through one of a plurality of series connected diode strings and for controlling a boost switching regulator according to the largest voltage drop. The electronic circuit can sense an open circuit series connected diode string, which would otherwise have the largest voltage drop, and can disconnect that open circuit series connected diode string from control of the boost switching regulator. Another electronic circuit includes a current limiting circuit coupled to or within a boost switching regulator and configured to operate with a diode load. Another electronic circuit includes a pulse width modulation circuit configured to dim a series connected string of light emitting diodes.

Claims25

Dependent claims

An electronic circuit, comprising:

a current regulator having a current sense node, wherein the current regulator is configured to pass a predetermined current through the current regulator;
an open-circuit detection circuit having an input node and an output node, wherein the input node of the open-circuit detection circuit is coupled to the current sense node of the current regulator, and wherein the open-circuit detection circuit is configured to provide an output signal at the output node of the open-circuit detection circuit indicative of a current flowing through the current regulator being below a predetermined current threshold;
and
a switch having an input node, an output node, and a control node, wherein the input node of the switch is coupled to the current sense node of the current regulator, wherein a selected one of the input node or the output node of the switch is coupled to the input node of open-circuit detection circuit, wherein the control node of the switch is coupled to the open-circuit detection circuit, and wherein the open-circuit detection circuit is configured to open the switch in response to the current flowing through the current regulator being below the predetermined current threshold.

1 more element

An electronic circuit for dimming a light emitting diode having an anode and a cathode, the electronic circuit comprising:

a current regulator having a current node and a control node, wherein the current node of the current regulator is configured to couple to the light emitting diode;
a boost switching regulator having an input node, an output node, and a control node, wherein the output node of the boost switching regulator is configured to couple to a selected one of the anode of the light emitting diode or to the current regulator, and wherein the boost switching regulator is enabled to switch or is disabled from switching in response to an input signal at the control node of the boost switching regulator;
and
a pulse width modulation circuit having an output node and a control node, wherein the output node of the pulse width modulation circuit is coupled to the control node of the current regulator, wherein the pulse width modulation circuit is configured to generate an AC output signal at the output node of the pulse width modulation circuit, which enables and disables the current regulator at a predetermined frequency and at a selected duty cycle in response to a respective selected input signal at the input node of the pulse width modulation circuit, wherein the duty cycle is selected in accordance with a selected brightness of the light emitting diode, and wherein, substantially simultaneously with the current regulator being disabled, the input signal at the control node of the switching regulator is indicative of the boost switching regulator being disabled.

1 more element

Dependencies are inferred from the claim text.