This application claims priority to and the benefit of Chinese Patent Application No. 201910491568.0, filed on Jun. 6, 2019, which is incorporated herein by reference in its entirety.
The present invention relates generally to electronic circuits, and more particularly but not exclusively to a dimming circuit of a light emitting device and a method thereof.
To meet the different brightness requirements of different applications, light emitting device dimming is necessary. The brightness of a LED (Light-emitting Diode), which is a widely adopted light emitting device today, depends on an average current flowing through the LED. That is to say, LED dimming could be realized by regulating the average current flowing through the LED. Currently, two techniques of regulating the average current flowing through the LED are popular, one is regulating an amplitude of the current flowing through the LED, and the other one is regulating a duty cycle of the current flowing through the LED.
In real applications, different dimming signals could be combined to realize LED dimming. However, multiple dimming signals may increase the complexity of a dimming circuit, and will need multiple dimming pins to receive the multiple dimming signals, which increase the size and cost of the dimming circuit.
It is an object of the present invention to provide a dimming chip with simple structure and a multi-function pin to process the dimming signal in multiple forms.
In accomplishing the above and other objects, there has been provided, in accordance with an embodiment of the present invention, a dimming circuit for dimming a current flowing through a light emitting device, comprising: a multi-function pin, configured to receive a dimming signal; wherein when the dimming signal is an analog voltage signal, an amplitude of the current flowing through the light emitting device is regulated based on the dimming signal; when the dimming signal is a pulse signal and a frequency of the dimming signal is in a first frequency range, a duty cycle of the current flowing through the light emitting device is regulated based on the dimming signal; and when the dimming signal is the pulse signal and the frequency of the dimming signal is in a second frequency range, the amplitude of the current flowing through the light emitting device is regulated based on the dimming signal.
In accomplishing the above and other objects, there has been provided, in accordance with an embodiment of the present invention, a control method of a dimming circuit adopted to control a dimming switch coupled in series with a light emitting device, comprising: receiving and detecting a dimming signal; regulating an amplitude of a current flowing through the light emitting device based on the dimming signal when the dimming signal is an analog voltage signal; detecting a frequency of the dimming signal when the dimming signal is a pulse signal; regulating a duty cycle of the current flowing through the light emitting device based on the dimming signal when the frequency of the dimming signal is in a first frequency range; and regulating the amplitude of the current flowing through the light emitting device based on the dimming signal when the frequency of the dimming signal is in a second frequency range.
In accomplishing the above and other objects, there has been provided, in accordance with an embodiment of the present invention, a control method of a dimming circuit adopted to control a dimming switch coupled in series with a light emitting device, comprising: receiving a dimming signal; dividing the dimming signal into a first frequency dimming signal and a second frequency dimming signal; regulating a duty cycle of the current flowing through the light emitting device based on the first frequency dimming signal; and regulating an amplitude of the current flowing through the light emitting device based on the second frequency dimming signal.
The use of the same reference label in different drawings indicates the same or like components.
In the present invention, numerous specific details are provided, such as examples of circuits, components, and methods, to provide a thorough understanding of embodiments of the invention. Persons of ordinary skill in the art would recognize, however, that the invention can be practiced without one or more of the specific details. In other instances, well-known details are not shown or described to avoid obscuring aspects of the invention.
In the example of
In one embodiment, when the frequency of the dimming signal DIM is lower than a first frequency threshold F1, the duty cycle of the current ILED flowing through the LED string is regulated; when the frequency of the dimming signal DIM is higher than a second frequency threshold F2, the amplitude of the current ILED flowing through the LED string is regulated; wherein the first frequency threshold F1 is lower than the second frequency threshold F2.
In one embodiment, the first frequency range is corresponding to a frequency between zero and the first frequency threshold F1, and the second frequency range is corresponding to a frequency larger than the second frequency threshold F2.
In one embodiment, when the frequency of the dimming signal DIM is higher than the second frequency threshold F2, the duty cycle of the current ILED flowing through the LED string is regulated; when the frequency of the dimming signal DIM is lower than the first frequency threshold F1, the amplitude of the current ILED flowing through the LED string is regulated. The regulation ways of the current ILED based on the dimming signal DIM could be determined according to the application requirements.
In one embodiment, the dimming circuit 20 further comprises a selecting circuit 206, configured to receive the default reference signal Vref0, the pulse reference signal Vref1, the analog reference signal Vref2, the amplitude regulating enable signal EN2 and the analog voltage regulating enable signal EN3, wherein the selecting circuit 206 selects the pulse reference signal vref1 as the dimming amplitude reference signal Vref when amplitude regulating enable signal EN2 is valid, and selects the analog reference signal Vref2 as the dimming amplitude reference signal Vref when the analog voltage regulating enable signal EN3 is valid, and selects the default reference signal Vref0 as the dimming amplitude reference signal Vref when neither of the amplitude regulating enable signal EN2 and the analog voltage regulating enable signal EN3 is valid.
In one embodiment, the selecting circuit 206 comprises a logic circuit and a multiplexer switch. The logic circuit performs logic operation to the amplitude regulating enable signal EN2 and the analog voltage regulating enable signal EN3. The multiplexer switch provides one of the default reference signal Vref0, the pulse reference signal Vref1 and the analog reference signal Vref2 as the dimming amplitude reference signal Vref based on the logic operation result.
In one embodiment, the selecting circuit 206 comprises a multiplexer switch. The amplitude regulating enable signal EN2 and the analog voltage regulating enable signal EN3 are provided to the multiplexer switch to control the multiplexer switch, and the multiplexer switch provides one of the default reference signal Vref0, the pulse reference signal Vref1 and the analog reference signal Vref2 as the dimming amplitude reference signal Vref under the control of the amplitude regulating enable signal EN2 and the analog voltage regulating enable signal EN3.
In one embodiment, the duty cycle regulating circuit 202 comprises a frequency converting circuit. When the duty cycle regulating enable signal EN1 is valid, i.e., the dimming signal DIM is a pulse signal and the frequency of the dimming signal DIM is in the first frequency range, the duty cycle regulating signal ENR is generated based on the dimming signal DIM, wherein the duty cycle regulating signal ENR is a pulse signal and may have a different frequency from the dimming signal DIM.
In some embodiments, the duty cycle regulating circuit 202 comprises a switch. When the duty cycle regulating enable signal EN1 is valid, the switch is turned on, and passes the dimming signal DIM to be the duty cycle regulating signal ENR.
In one embodiment, the amplitude regulating circuit 203 comprises a frequency-voltage converting circuit. When the amplitude regulating enable signal EN2 is valid, the dimming signal DIM is converted by the amplitude regulating circuit 203 to the pulse reference signal Vref1. The value of the pulse reference signal Vref1 is in proportional to the frequency of the dimming signal DIM. In some embodiments, the amplitude regulating circuit 203 comprises a filter circuit. In some embodiments, the amplitude regulating circuit 203 comprises a digital-to-analog converting circuit. It should be understood that any circuit could convert a pulse signal to a voltage signal could be adopted to convert the dimming signal DIM to the pulse reference signal vref1.
In one embodiment, the analog regulating circuit 204 comprises a scaling circuit. When the analog voltage regulating enable signal EN3 is valid, i.e., the dimming signal DIM is an analog signal, the dimming signal DIM is converted to the analog reference signal Vref2, wherein the value of the analog reference signal Vref2 is in proportional to the value of the dimming signal DIM. In some embodiments, the value of the analog reference signal Vref2 is equal to the value of the dimming signal DIM.
In one embodiment, the analog voltage detecting circuit 401 comprises a rising edge detecting circuit or a falling edge detecting circuit. When no rising edge or no falling edge is detected in a preset time period, the analog voltage detecting circuit 401 provides a valid analog voltage regulating enable signal EN3, otherwise, the analog voltage detecting circuit 401 provides an invalid voltage regulating enable signal EN3. It should be understood that any circuit could detect if a signal is an analog signal or a pulse signal could be used with present invention.
In one embodiment, the frequency detecting circuit 402 detects the frequency of the dimming signal DIM. When the frequency of the dimming signal DIM is in the first frequency range, the duty cycle regulating enable signal EN1 is valid. When the frequency of the dimming signal DIM is in the second frequency range, the amplitude regulating enable signal EN2 is valid.
In some applications, when dimming enable signal EN0 disables the amplifying circuit 205 when the dimming signal DIM is detected to be in a specific voltage form for a preset time period Tdisable.
The operation of the dimming circuit 50 is similar with the operation of the dimming circuit 20, and is not described here for brevity.
In the example of
In one embodiment, the duty cycle regulating circuit 702 comprises a frequency converting circuit to convert the first frequency dimming signal LDIM to the duty cycle regulating signal ENR. In some embodiments, the duty cycle regulating circuit 702 is omitted and the first frequency dimming signal LDIM is provided as the duty cycle regulating signal ENR to the amplifying circuit 205.
In one embodiment, the amplitude regulating circuit 703 comprises a frequency-voltage converting circuit to convert the second frequency dimming signal HDIM to the pulse reference signal Vref1. The value of the pulse reference signal Vref1 is in proportional to the frequency of the second frequency dimming signal HDIM.
In one embodiment, the dimming signal DIM provided to the dimming circuit 70 may comprise dimming enable information. In one embodiment, the dimming circuit 70 further comprises the dimming enable circuit 601 in
Step 801, receiving and detecting a dimming signal DIM;
Step 802, regulating an amplitude of a current flowing through the light emitting device based on the dimming signal DIM if the dimming signal DIM is an analog voltage signal;
Step 803, detecting a frequency of the dimming signal DIM if the dimming signal DIM is a pulse signal;
Step 804, regulating a duty cycle of the current flowing through the light emitting device based on the dimming signal DIM if the frequency of the dimming signal DIM is in a first frequency range; and
Step 805, regulating the amplitude of the current flowing through the light emitting device based on the dimming signal DIM if the frequency of the dimming signal DIM is in a second frequency range.
Wherein, regulating the amplitude of the current flowing through the light emitting device based on the dimming signal DIM comprises: converting the dimming signal DIM to a dimming amplitude reference signal; generating a switching control signal based on amplifying a difference between the dimming amplitude reference signal and a feedback signal indicating the current flowing through the light emitting device; and controlling the dimming switch based on the switching control signal.
In one embodiment, regulating the amplitude of the current flowing through the light emitting device further comprises: maintaining the duty cycle of the current flowing through the light emitting device be 100%.
In one embodiment, regulating the duty cycle of the current flowing through the light emitting device based on the dimming signal DIM comprises: enabling and disabling alternatively an amplifying circuit configured to amplify a difference between the dimming amplitude reference signal and a feedback signal indicating the current flowing through the light emitting device, based on the dimming signal DIM.
In one embodiment, regulating the duty cycle of the current flowing through the light emitting device based on the dimming signal DIM further comprises: maintaining the amplitude of the current flowing through the light emitting device be a preset constant value.
In one embodiment, a maximum frequency in the first frequency range is lower than a minimum frequency in the second frequency range.
In one embodiment, the control method 80 further comprises: disabling the dimming circuit when a value of the dimming signal DIM keeps a specific signal form for a preset time period Tdisable.
Obviously many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described. It should be understood, of course, the foregoing disclosure relates only to a preferred embodiment (or embodiments) of the invention and that numerous modifications may be made therein without departing from the spirit and the scope of the invention as set forth in the appended claims. Various modifications are contemplated and they obviously would be resorted to by those skilled in the art without departing from the spirit and the scope of the invention as hereinafter defined by the appended claims as only a preferred embodiment(s) thereof has been disclosed.
Number | Date | Country | Kind |
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201910491568.0 | Jun 2019 | CN | national |
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Number | Date | Country | |
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20200389953 A1 | Dec 2020 | US |