LED driver, LED driving method and controller for LED driver

Patent metadata

Field	Value
Publication number	US-9449546-B2
Application number	US-201414582011-A
Country	US
Kind code	B2
Filing date	Dec 23, 2014
Priority date	Dec 23, 2013
Publication date	Sep 20, 2016
Grant date	Sep 20, 2016

Abstract

A LED driver, a LED driving method and a controller for LED driver are discussed in the present invention. The LED driver detects the phase of the input signal which is phase cut by a triac from a pre-E-transformer. The LED driver regulates the current flowing through the LED strings by varying the phase of the input signal.

First claim

We claim:

1. A control circuit used in a LED driver, the LED driver includes an input port configured to receive an input signal, an output port configured to provide a driving voltage to a LED string, an intermediate node, a step-up stage having a first power switch coupled between the input port and the intermediate node, and a step-down stage having a second power switch and a third power switch coupled between the intermediate node and the output port, the control circuit comprising:
a phase detector, having an input terminal coupled to the input port to receive the input signal, a first output terminal configured to generate a phase detecting signal indicative of phase information of the input signal, and a second output terminal configured to generate a cycle detecting signal indicative of cycle information of the input signal, wherein the cycle detecting signal is a short pulse signal;
a step-up comparator, having a first input terminal configured to receive a reference signal, a second input terminal configured to receive a voltage feedback signal indicative of a voltage at the Intermediate node, and an output terminal configured to generate a step-up comparison signal based on the reference signal and the voltage feedback signal;
a logical OR unit, having a first input terminal coupled to the second output terminal of the phase detector to receive the cycle detecting signal, a second input terminal coupled to the output terminal of the step-up comparator to receive the step-up comparison signal, and an output terminal configured to generate a step-up enable signal by executing logical OR operation on the cycle detecting signal and the step-up comparison signal;
a step-up controller, coupled to the logical OR unit to receive the step-up enable signal, to get enabled or disabled by the step-up enable signal, and to generate a step-up control signal, the step-up control signal being used to control the first power switch;
a logical AND unit, having a first input terminal coupled to the first output terminal of the phase detector to receive the phase detecting signal, a second input terminal coupled to the step-up comparator to receive the step-up comparison signal, and an output terminal configured to generate a logical AND signal by executing logical AND operation on the phase detecting signal and the step-up comparison signal;
an average circuit, coupled to the output terminal of the logical AND unit to receive the logical AND signal and to generate an average signal; and
a step-down controller, having a first input terminal configured to receive a LED current sense signal indicative of a current flowing through the LED string, a second input terminal coupled to the average circuit to receive the average signal, and an output terminal configured to generate a step-down control signal to control the second power switch and the third power switch.

2. The control circuit of claim 1 , wherein the step-down controller comprises:
an error amplifier, having a first input terminal configured to receive the LED current sense signal, a second input terminal coupled to the average circuit to receive the average signal, and an output terminal configured to generate an error amplified signal;
a step-down comparator, having a first input terminal coupled to the output terminal of the error amplifier to receive the error amplified signal, a second input terminal configured to receive an inductor current sense signal indicative of a current flowing through the second power switch, and an output terminal configured to generate a step-down comparison signal; and
a control and logical circuit, coupled to the step-down comparator to receive the step-down comparison signal, and to generate the step-down control signal based on the step-down comparison signal.

3. The control circuit of claim 1 , the average circuit comprises an average resistor and an average capacitor coupled in series between the output terminal of the logical AND unit and the reference ground, wherein the average signal is generated at the conjunction node of the average resistor and the average capacitor.

4. The control circuit of claim 1 , wherein the phase detector comprises:
a phase comparator, having a first input terminal configured to receive a threshold signal, a second input terminal configured to receive the input signal, and an output terminal configured to generate the phase detecting signal based on the threshold signal and the input signal; and
a short pulse circuit, coupled to the output terminal of the phase comparator to receive the phase detecting signal, and to generate the cycle detecting signal with a short pulse in response to a falling edge of the phase detecting signal.

5. The control circuit of claim 1 , wherein the step-up comparator comprises a hysteresis comparator.

6. A LED driver, comprising:
an input port, configured to receive an input signal, wherein the input signal is a phase cut voltage from a pre-E-transformer, the pre-E-transformer is with triac;
an output port, configured to provide a driving voltage;
an Intermediate node;
an input capacitor, coupled between the input port and a reference ground;
a first inductor and a diode, series coupled between the input port and the Intermediate node;
a first power switch, coupled between the reference ground and the conjunction node of the first inductor and the diode;
an Intermediate capacitor, coupled between the Intermediate node and the reference ground;
a second power switch and a second inductor, series coupled between the Intermediate node and the output port;
a third power switch, coupled between the reference ground and the conjunction node of the second power switch and the second inductor;
an output capacitor, coupled between the output port and the reference ground;
a LED string and a sense resistor, series coupled between the output port and the reference ground;
a phase detector, having an input terminal coupled to the input port to receive the input signal, a first output terminal configured to generate a phase detecting signal indicative of phase information of the input signal, and a second output terminal configured to generate a cycle detecting signal indicative of cycle information of the input signal, wherein the cycle detecting signal is a short pulse signal;
a step-up comparator, having a first input terminal configured to receive a reference signal, a second input terminal configured to receive a voltage feedback signal indicative of a voltage at the Intermediate node, and an output terminal configured to generate a step-up comparison signal based on the reference signal and the voltage feedback signal;
a logical OR unit, having a first input terminal coupled to the second output terminal of the phase detector to receive the cycle detecting signal, a second input terminal coupled to the output terminal of the step-up comparator to receive the step-up comparison signal, and an output terminal configured to generate a step-up enable signal by executing logical OR operation on the cycle detecting signal and the step-up comparison signal;
a step-up controller, coupled to the logical OR unit to receive the step-up enable signal, to get enabled or disabled by the step-up enable signal, and to generate a step-up control signal, the step-up control signal being used to control the first power switch;
a logical AND unit, having a first input terminal coupled to the first output terminal of the phase detector to receive the phase detecting signal, a second input terminal coupled to the step-up comparator to receive the step-up comparison signal, and an output terminal configured to generate a logical AND signal by executing logical AND operation on the phase detecting signal and the step-up comparison signal;
an average circui

Assignees

• Chengdu Monolithic Power Sys

Inventors

• Kuang Naixing
• Yu Jiaqi
• Ren Yuancheng

Classifications

• G09G2330/028

  Generation of voltages supplied to electrode drivers in a matrix display other than LCD · CPC title

• H05B33/00

  Electroluminescent light sources · CPC title

• H02M3/158

  including plural semiconductor devices as final control devices for a single load · CPC title

• G09G2310/0289

  Details of voltage level shifters arranged for use in a driving circuit · CPC title

• H05B33/08

  Electricity · mapped topic