US 8,569,975 B2 · Control circuit for switching power supply

Abstract

A control IC controls a switching power supply configured to supply a driving voltage Vout to one terminal of an LED string which is driven in an intermittent manner. A sample-and-hold circuit performs sampling of a detection voltage Vs that corresponds to a driving voltage Vout in the on period, and holds the sampled detection voltage Vs in the off period. In the off period, a pulse modulator generates a pulse signal having a duty ratio adjusted such that a hold detection voltage VsH output from the sample-and-hold circuit matches the detection voltage Vs. A driver drives a switching transistor according to the pulse signal.

Claims12

Dependent claims

A control circuit for a switching power supply configured to supply a driving voltage to one terminal of a light emitting element configured to be intermittently driven, the control circuit comprising:

a sample-and-hold circuit configured to (i) sample a detection voltage that corresponds to the driving voltage generated in an on period of the light emitting element, and (ii) to hold the detection voltage thus sampled and to output a hold detection voltage that corresponds to the detection voltage in an off period of the light emitting element, the hold detection voltage being higher than the detection voltage;
a pulse modulator configured to generate a pulse signal having a duty ratio adjusted in an off period of the light emitting element such that the detection voltage matches a hold detection voltage output from the sample-and-hold circuit;
and
a driver configured to drive a switching element of the switching power supply according to the pulse signal.

1 more element

A light emitting apparatus comprising:

a plurality of light emitting elements;
a switching power supply configured to supply an independent driving voltage to one terminal of each of the plurality of light emitting elements;
and
a current driving circuit configured to supply, to each of the plurality of light emitting elements, an intermittent driving current that corresponds to a target luminance,
wherein the switching power supply comprises:
an output circuit comprising a switching element;
and
a control circuit configured to drive the switching elements,
and wherein the control circuit comprises:
a sample-and-hold circuit configured to (i) sample a detection voltage that corresponds to the driving voltage generated in an on period of the light emitting element, and (ii) to hold the detection voltage thus sampled and to output a hold detection voltage that corresponds to the detection voltage in an off period of the light emitting element, the hold detection voltage being higher than the detection voltage;
a pulse modulator configured to generate a pulse signal having a duty ratio adjusted in an off period of the light emitting element such that the detection voltage matches a hold detection voltage output from the sample-and-hold circuit;
and
a driver configured to drive a switching element of the switching power supply according to the pulse signal,
and wherein the output circuit comprises:
an input terminal via which an input voltage is to be applied;
a plurality of output terminals via which the driving voltages are respectively output to the respective multiple light emitting elements;
an inductor and a switching element sequentially connected in series between the input terminal and a fixed voltage terminal;
a plurality of rectifier elements respectively provided to the multiple output terminals, and arranged such that one terminal of each of the rectifier elements is connected to a corresponding output terminal, and the other terminal of each of the rectifier elements is connected to a connection node that connects the inductor and the switching element;
and
a plurality of output capacitors respectively provided to the multiple output terminals, and each arranged between a corresponding output terminal and the fixed voltage terminal.

17 more elements

An electronic device comprising:

a liquid crystal panel;
and
a light emitting apparatus arranged as a backlight of the liquid crystal panel, the light emitting apparatus comprising:
a plurality of light emitting elements;
a switching power supply configured to supply an independent driving voltage to one terminal of each of the plurality of light emitting elements;
and
a current driving circuit configured to supply, to each of the plurality of light emitting elements, an intermittent driving current that corresponds to a target luminance,
wherein the switching power supply comprises:
an output circuit comprising a switching element;
and
a control circuit configured to drive the switching elements,
and wherein the control circuit comprises:
a sample-and-hold circuit configured to (i) sample a detection voltage that corresponds to the driving voltage generated in an on period of the light emitting element, and (ii) to hold the detection voltage thus sampled and to output a hold detection voltage that corresponds to the detection voltage in an off period of the light emitting element, the hold detection voltage being higher than the detection voltage;
a pulse modulator configured to generate a pulse signal having a duty ratio adjusted in an off period of the light emitting element such that the detection voltage matches a hold detection voltage output from the sample-and-hold circuit;
and
a driver configured to drive a switching element of the switching power supply according to the pulse signal, and wherein the output circuit comprises:
an input terminal via which an input voltage is to be applied;
a plurality of output terminals via which the driving voltages are respectively output to the respective multiple light emitting elements;
an inductor and a switching element sequentially connected in series between the input terminal and a fixed voltage terminal;
a plurality of rectifier elements respectively provided to the multiple output terminals, and arranged such that one terminal of each of the rectifier elements is connected to a corresponding output terminal, and the other terminal of each of the rectifier elements is connected to a connection node that connects the inductor and the switching element;
and
a plurality of output capacitors respectively provided to the multiple output terminals, and each arranged between a corresponding output terminal and the fixed voltage terminal.

19 more elements

Dependencies are inferred from the claim text.

Control circuit for switching power supply

Life of this patent

Control circuit for switching power supply

Life of this patent

Abstract

Claims12