Dimming circuit

Patent metadata

Field	Value
Publication number	US-11617248-B2
Application number	US-202117643418-A
Country	US
Kind code	B2
Filing date	Dec 9, 2021
Priority date	May 26, 2020
Publication date	Mar 28, 2023
Grant date	Mar 28, 2023

Abstract

A dimming control method and a dimming circuit are used to control the brightness of a LED. The dimming circuit includes a power conversion unit having an input end, an output end, an inductor, and a switch. When the dimming current signal is higher than or equal to a first current threshold, the switch is controlled such that the power conversion unit operates in a continuous Conduction mode or a boundary Conduction mode; when the dimming current signal is lower than the first current threshold, the switch is controlled such that the power conversion unit operates in a discontinuous Conduction mode; and when the dimming current signal is lower than a second current threshold, the switch is controlled such that the power conversion unit operates in a chopping control mode.

First claim

What is claimed is:

1. A dimming circuit for controlling the brightness of a light emitting diode, comprising:
a power conversion unit having an input end, an output end, an inductor and a switch, the power conversion unit configured to receive an input voltage from the input end, and convert the input voltage into an output voltage output from the output end by operation of the switch;
an input voltage sampling circuit configured to generate an input voltage sampling signal by detecting the input voltage;
an output voltage sampling circuit configured to generate an output voltage sampling signal by detecting the output voltage;
a current sampling circuit configured to generate a current sampling signal by detecting a current flowing through the switch;
a dimming signal sampling circuit configured to receive a dimming signal to calculate and generate a dimming current signal;
a driving circuit connected to the switch for driving the switch to turn on or turn off; and
a control unit configured to receive the input voltage sampling signal, the output voltage sampling signal, the current sampling signal and the dimming current signal, and output a control signal to the driving circuit to control the switch; wherein,
the control unit compares the dimming current signal with a first current threshold and a second current threshold,
when the dimming current signal is higher than or equal to the first current threshold, the control unit controls the switch such that the power conversion unit operates in a continuous conduction mode or a boundary conduction mode;
when the dimming current signal is lower than the first current threshold, the control unit controls the switch such that the power conversion unit operates in a discontinuous conduction mode; and
in the discontinuous conduction mode, when the dimming current signal is lower than the second current threshold, the control unit controls the switch such that the power conversion unit operates in a chopping control mode.

2. The dimming circuit according to claim 1 , wherein the control unit comprises:
a dimming processing module configured to set a peak current reference according to the dimming current signal;
a comparator module configured to compare the current sampling signal with the peak current reference, and output a corresponding compared output signal according to a comparing result;
a switching time calculation module configured to calculate a switching period or an on time or an off time of the switch; and
a timer module configured to receive the compared output signal and the switching period or the on time or the off time of the switch, and output the control signal formed of a plurality of pulses.

3. The dimming circuit according to claim 2 , wherein when the dimming current signal is higher than or equal to the first current threshold, the control unit controls the switch such that the power conversion unit operates in a continuous conduction mode; wherein,
the switching time calculation module calculates the off time of the switch according to the output voltage sampling signal, a set ripple current reference, and an inductance of the inductor.

4. The dimming circuit according to claim 3 , wherein,
when the current sampling signal is equal to the peak current reference, the comparator module outputs a reset signal, and the timer module clears counting and output a low level when detecting the reset signal;
when the timer module starts counting from zero, and a counter value increases to a first compare value, an output of the timer module is flipped over to a high level, thereby outputting the control signal formed of a plurality of pulses, such that the power conversion unit operates in the continuous conduction mode; wherein the first compare value corresponds to the off time of the switch.

5. The dimming circuit according to claim 4 , wherein the off time of the switch is calculated by the following formula:

T
off

=

I
pp

·

L

V
out

;

wherein T off is the off time of the switch, V out is the output voltage, I pp is the ripple current reference, and L is the inductance of the inductor.

6. The dimming circuit according to claim 4 , wherein when the dimming current signal is higher than or equal to the second current threshold and lower than the first current threshold, the switching time calculation module sets a fixed switching period and calculates the on time of the switch according to the input voltage sampling signal, the output voltage sampling signal and the dimming current signal, and the control unit controls the power conversion unit to operate in a constant frequency discontinuous conduction mode by altering a duty cycle of the control signal.

7. The dimming circuit according to claim 4 , wherein,
when the dimming current signal is higher than or equal to a third current threshold and lower than the first current threshold,
the switching time calculation module calculates the switching period of the switch according to the input voltage sampling signal, the output voltage sampling signal, the dimming current signal, and the ripple current reference; and
the switching time calculation module calculates the on time of the switch according to the input voltage sampling signal, the output voltage sampling signal, and the ripple current reference, and the control unit controls the power conversion unit to operate in a variable frequency discontinuous conduction mode.

8. The dimming circuit according to claim 7 , wherein,
the switching period of the switch is calculated by the following formula:

T
s

=

I
pp
2

·
L
·

V
in

2
·

I
dim

·

V
out

·

(

V
in

-

V
out

)

;

wherein T s is the switching period of the switch, I pp is the ripple current reference, L is the inductance of the inductor, V in is the input voltage, I dim is the dimming current signal, and V out is the output voltage; and
the on time of the switch is calculated by the following formula:

Assignees

• Delta Electronics Shanghai Co

Inventors

• Bao Yugang
• Zhang Xinghua
• Fu Xiaoping

Classifications

• Y02B20/30

  Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED] · CPC title

• H05B45/375 Primary

  using buck topology · CPC title

• H05B45/50

  responsive to malfunctions or undesirable behaviour of LEDs; responsive to LED life; Protective circuits · CPC title

• H05B45/10 Primary

  Controlling the intensity of the light · CPC title