TWI759040B - Dimming control circuit and method - Google Patents

Abstract

A dimming control circuit and method are provided. The dimming control circuit comprises: a dimming signal input port, operable to receive the dimming signal from the outside; a voltage clamping circuit, operable to generate a clamped dimming signal by clamping the dimming signal; a filter circuit, The dimming amplifier is operable to generate a dimming control signal by filtering the clamped dimming signal; An output signal that controls the brightness of the light source. The dimming control circuit and method according to the embodiments of the present invention can receive dimming signals of different modes through the same dimming signal input port, and perform dimming control in a self-adjusting manner according to the type of the received dimming signal, so it can effectively Reduce chip pin resources for integrated circuit applications.

Description

Dimming control circuit and method

The present invention relates to the field of circuits, and more particularly to a dimming control circuit and method.

In the application system for controlling the light source, it is often necessary to control the brightness of the light source. The current dimming control circuit mainly uses a pulse width modulation (Pulse Width Modulation, PWM) signal or an analog voltage signal to control the brightness of the light source.

FIG. 1 shows a schematic diagram of a current dimming control circuit 100 . As shown in FIG. 1 , the current dimming control method is that the dimming control circuit 100 implements the dimming control based on the PWM dimming signal and the analog voltage dimming signal entered through the first input port and the second input port.

In the dimming control circuit 100 shown in FIG. 1 , the level conversion circuit 102 generates the dimming control signal Vs by converting the analog voltage dimming signal, and the dimming amplifier 106 performs the analog dimming control based on the dimming control signal Vs. Since the dimming control method based on the PWM dimming signal will have a stroboscopic problem, generally, the PWM dimming signal is first converted into a DC analog signal, and then the analog dimming control is performed based on the DC analog signal. Specifically, the PWM sensing circuit 104 converts the PWM dimming signal to generate a pulse signal dimming with the same working factor as the PWM dimming signal and a fixed high level (the level is VH). The filter circuit 108 composed of the resistor R11 and the capacitor C11 The dimming control signal Vs is generated by filtering the pulse signal dimming, and the dimming amplifier 106 performs analog dimming control based on the dimming control signal Vs.

In the dimming control circuit 100 shown in FIG. 1 , the dimming amplifier 106 adjusts the magnitude of the feedback signal FB, which can reflect the brightness of the light source, which is input according to the magnitude of the dimming control signal Vs, so as to generate a signal for adjusting the brightness of the light source. The control output signal Vc, the output signal Vc is subjected to pulse width modulation, pulse frequency modulation (Pulse Frequency Modulation, Closed-loop control such as PFM), or linear control realizes the control of the brightness of the light source.

The dimming control circuit 100 shown in FIG. 1 requires at least two dimming signal input ports. For integrated circuits including dimming control functions, more pin resources will increase the chip cost and system size.

In view of one or more of the above problems, the present invention provides a novel dimming control circuit and method.

A dimming control circuit according to an embodiment of the present invention includes: a dimming signal input port operable to receive a dimming signal from the outside; a voltage clamping circuit operable to generate a clamping dimming by clamping the dimming signal a light signal; a filter circuit operable to generate a dimming control signal by filtering the clamped dimming signal; and a dimming amplifier operable to adjust a feedback signal capable of reflecting the brightness of the light source by adjusting the magnitude of the dimming control signal The size of the output signal is used to control the brightness of the light source.

The dimming control method according to the embodiment of the present invention includes: receiving a dimming signal from the outside through a dimming signal input port; generating a clamped dimming signal by clamping the dimming signal; The filtering process generates a dimming control signal; and the output signal for controlling the brightness of the light source is generated by adjusting the magnitude of the feedback signal capable of reflecting the brightness of the light source according to the magnitude of the dimming control signal.

The dimming control circuit and method according to the embodiments of the present invention can receive dimming signals of different modes through the same dimming signal input port, and perform dimming control in a self-adjusting manner according to the type of the received dimming signal, so it can effectively Reduce die pin resources in integrated circuit applications.

100,200,300,400: Dimming control circuit

102: Level conversion circuit

104: PWM sensing circuit

106, 206: Dimming amplifiers

108,204: Filter circuit

202: Voltage clamping circuit

302: Low level control circuit

C2: Compensation Capacitor

C11, C21, C71: Capacitors

DIM: Dimming signal input port

dimming: pulse signal

FB: feedback signal

K2: switch

M1, M2: Adjust transistor

Q1, Q4: voltage comparator

Q2: Buffer Amplifier

Q3: Amplifier

R11, R21, R22: Resistors

Vc: output signal

Vcp: clamp dimming signal

V _DIM : Dimming signal

VH: clamp voltage

VL: reference level

Vs: Dimming control signal

The present invention can be better understood from the following description of specific embodiments of the present invention in conjunction with the drawings, wherein:

FIG. 1 shows a schematic diagram of a current dimming control circuit;

FIG. 2 shows a schematic diagram of a dimming control circuit according to an embodiment of the present invention;

3A shows the relationship between the dimming control signal Vs and the operating factor of the dimming signal V _DIM when the dimming signal V _DIM is a PWM dimming signal;

3B shows the relationship between the dimming control signal Vs and the dimming signal V _DIM when the dimming signal V _DIM is an analog voltage dimming signal;

FIG. 4A shows a schematic diagram of an example implementation of a voltage clamping circuit in the dimming control circuit shown in FIG. 2;

FIG. 4B shows a schematic diagram of another example implementation of the voltage clamping circuit in the dimming control circuit shown in FIG. 2;

FIG. 5 shows a schematic diagram of a dimming control circuit according to another embodiment of the present invention;

FIG. 6 shows a dimming characteristic curve of the dimming control circuit shown in FIG. 5 when the dimming signal V _DIM is an analog voltage dimming signal;

FIG. 7 shows a schematic diagram of a dimming control circuit according to yet another embodiment of the present invention.

Features and exemplary embodiments of various aspects of the invention are described in detail below. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to one skilled in the art that the present invention may be practiced without some of these specific details. The following description of the embodiments is only intended to provide a better understanding of the present invention by illustrating examples of the invention. The present invention is in no way limited to any specific configurations and algorithms set forth below, but covers any modification, substitution and improvement of elements, components and algorithms without departing from the spirit of the invention. In the drawings and the following description, well-known structures and techniques have not been shown in order to avoid unnecessarily obscuring the present invention.

In view of one or more problems existing in the current dimming control circuit, the present invention proposes a novel dimming control circuit and method. The dimming control circuit and method according to the embodiments of the present invention can receive dimming signals of different modes through the same dimming signal input port, and perform dimming control in a self-adjusting manner according to the type of the received dimming signal, so it can effectively Reduce chip pin resources for integrated circuit applications.

FIG. 2 shows a schematic diagram of a dimming control circuit 200 according to an embodiment of the present invention. intention. As shown in FIG. 2, the dimming control circuit 200 includes a dimming signal input port DIM, a resistor R21, a voltage clamping circuit 202, a filter circuit 204 (for example, an RC filter circuit composed of a resistor R22 and a capacitor C21), and a dimming circuit The amplifier 206, wherein: the dimming signal input port DIM is operable to receive the dimming signal from the outside; the voltage clamping circuit 202 is operable to generate a clamped dimming signal by clamping the dimming signal; the filter circuit 204 is operable The dimming control signal is generated by filtering the clamped dimming signal; the dimming amplifier 206 is operable to generate a dimming control signal for the light source by adjusting the magnitude of the feedback signal that can reflect the brightness of the light source according to the magnitude of the dimming control signal. Brightness control output signal.

In some embodiments, as shown in FIG. 2 , the dimming signal V _DIM enters the dimming control circuit 200 through the dimming signal input port DIM; the voltage clamping circuit 202 clamps the dimming signal V _DIM after passing through the resistor R21 to generate the clamped dimming signal Vcp; the filter circuit 204 filters the clamped dimming signal Vcp to generate the dimming control signal Vs; the dimming control signal Vs is input to the forward input terminal of the dimming amplifier 206, the dimming amplifier 206 adjusts the magnitude of the feedback signal FB input to the reverse input terminal of the dimming control signal Vs according to the magnitude of the dimming control signal Vs to generate the output signal Vc. Here, the output signal Vc controls the brightness of the light source through closed-loop control such as PWM or PFM.

In some embodiments, the voltage clamping circuit 202 clamps the dimming signal V _DIM based on the preset clamping voltage VH, that is, when the dimming signal V _DIM is higher than the clamping voltage VH, the dimming signal V _DIM is clamped. It is clamped at the clamping voltage VH, so that the clamping dimming signal Vcp=VH. When the dimming signal V _DIM is an analog voltage dimming signal, Vs=Vcp; when the dimming signal V _DIM is a PWM dimming signal, Vs=VH*Duty, where Duty is the working factor of the dimming signal V _DIM .

In some embodiments, when the dimming signal V _DIM is a PWM dimming signal, the logic high level of the dimming signal V _DIM needs to be higher than the clamping voltage VH of the voltage clamping circuit 202 . At this time, the dimming control signal Vs and the The relationship between the operating factors of the dimming signal V _DIM is shown in FIG. 3A . The magnitude of the dimming control signal Vs can be adjusted by adjusting the working factor of the dimming signal V _DIM , thereby adjusting the brightness of the light source.

In some embodiments, when the dimming signal V _DIM is an analog voltage dimming signal, the relationship between the dimming control signal Vs and the dimming signal V _DIM is shown in FIG. 3B . When the dimming signal V _DIM is higher than the clamping voltage VH, the dimming control signal Vs is clamped at the clamping voltage VH. By adjusting the magnitude of the dimming signal V _DIM , the magnitude of the dimming control signal Vs can be adjusted, thereby adjusting the brightness of the light source.

FIG. 4A shows a schematic diagram of an example implementation of a voltage clamping circuit in the dimming control circuit shown in FIG. 2 . In some embodiments, as shown in FIG. 4A , the voltage clamping circuit 202 includes a regulating transistor M1, a compensation capacitor C2, and an amplifier Q3. One end of the voltage clamping circuit 202 is connected to the clamping voltage VH, and the other end is connected to the clamped voltage VH. circuit node. When the dimming signal V _DIM is not higher than the clamping voltage VH, the amplifier Q3 controls the adjustment transistor M1 to be in an off state, so that the voltage clamping circuit 202 does not work, and the clamping dimming signal Vcp is equal to the dimming signal V _DIM ; when When the dimming signal V _DIM is higher than the clamping voltage VH, the amplifier Q3 controls the adjustment transistor M1 to be turned on, so that the dimming signal V _DIM is pulled down to the clamping voltage VH by the adjustment transistor M1, so that the clamping dimming signal Vcp is It is equal to the clamping voltage VH, that is, the voltage clamping function is realized. The compensation capacitor C2 is connected between the gate electrode and the drain electrode of the adjustment transistor M1 for maintaining the stability of the voltage clamping circuit 202 .

FIG. 4B shows a schematic diagram of another example implementation of the voltage clamping circuit in the dimming control circuit shown in FIG. 2 . In some embodiments, as shown in FIG. 4B , the voltage clamping circuit 202 includes a voltage comparator Q1, a buffer amplifier Q2, and a switch K2; the inverting input terminal of the voltage comparator Q1 is connected to the clamping voltage VH, and the non-inverting input terminal is connected to the clamping voltage VH. It is connected to the dimming signal input port DIM; the forward input end of the buffer amplifier Q2 is connected to the clamping voltage VH, and the reverse input end is connected to the output end. At this time, the output voltage of the buffer amplifier Q2 is VH. When the dimming signal V _DIM is not higher than the clamping voltage VH, the voltage comparator Q1 controls the switch K2 to be connected to the dimming signal input port DIM. At this time, the clamping dimming signal Vcp is equal to the dimming signal V _DIM ; When V _DIM is higher than the clamping voltage VH, the voltage comparator Q1 controls the switch K2 to connect to the output end of the buffer amplifier Q2, and the dimming signal Vcp=VH is clamped at this time, thereby realizing the voltage clamping function.

In other words, the voltage comparator Q1 is operable to control the switch K2 to connect to the output terminal of the buffer amplifier Q2 when the dimming signal V _DIM is higher than the clamping voltage VH, so that the clamping dimming signal Vcp is equal to the clamping voltage VH; and It is operable to control the switch K2 to be connected to the dimming signal input port DIM when the dimming signal V _DIM is not higher than the clamping voltage VH , so that the clamping dimming signal Vcp is equal to the dimming signal V _DIM .

Considering that when the dimming signal V _DIM is a PWM dimming signal, the logic low level of the dimming signal V _DIM is often not the ideal 0V level, for example, higher than 0V, which will cause the dimming control signal Vs to be greater than the ideal voltage. Value VH*Duty.

FIG. 5 shows a schematic diagram of a dimming control circuit 300 according to another embodiment of the present invention. The difference between the dimming control circuit 300 shown in FIG. 5 and the dimming control circuit 200 shown in FIG. 2 is that a low-level control circuit 302 is connected between the clamped circuit node and the filter circuit 204 . The low level control circuit 302 includes a voltage comparator Q4 and a regulating transistor M2. The forward input terminal of the voltage comparator Q4 is connected to the reference level VL (VL<VH), and the reverse input terminal is connected to the clamping dimming signal Vcp. When the clamped dimming signal Vcp is not lower than the reference level VL, the voltage comparator Q4 outputs a low level to keep the adjustment transistor M2 in an off state, and the clamped dimming signal Vcp is not controlled by the low-level control circuit 302 . When the clamped dimming signal Vcp is lower than the reference level VL, the voltage comparator Q4 outputs a high level to make the adjustment transistor M2 turn on, and the clamped dimming signal Vcp is pulled down to 0V by the adjustment transistor M2. In this way, when the dimming signal is a PWM dimming signal, as long as the low level of the dimming signal is less than VL, an ideal dimming control signal Vs=VH*Duty can be generated.

The dimming control circuit 300 shown in FIG. 5 partially changes the dimming characteristics when the dimming signal V _DIM is an analog voltage dimming signal. FIG. 6 shows a dimming characteristic curve of the dimming control circuit shown in FIG. 5 when the dimming signal V _DIM is an analog voltage dimming signal. As shown in FIG. 6 , in the dimming control circuit 300 shown in FIG. 5 , the analog dimming range is between VL and VH. When the dimming signal V _DIM is a PWM dimming signal, the dimming characteristics of the dimming control circuit 300 shown in FIG. 5 are the same as those of the dimming control circuit 200 shown in FIG. 2 , that is, as shown in FIG. 3A . .

FIG. 7 shows a schematic diagram of a dimming control circuit 400 according to yet another embodiment of the present invention. The difference between the dimming control circuit 400 shown in FIG. 7 and the dimming control circuit 300 shown in FIG. 5 is that the filter circuit 204 is not included, and the clamped dimming signal Vcp directly enters the forward input terminal of the dimming amplifier 206 to adjust the The optical amplifier 206 utilizes its own characteristics (eg, using a transconductance amplifier structure and an equivalent output capacitor) and its compensation capacitor C71 to clamp the dimming signal The filtering function of Vcp. That is, the characteristics of the dimming amplifier 206 and the compensation capacitor realize a filter circuit that generates the dimming control signal Vs by filtering the clamped dimming signal Vcp. Here, the output signal Vc of the dimming amplifier 206 is controlled by closed-loop control such as PWM or PFM to control the brightness of the light source.

It should be noted that the dimming signal V _DIM , the clamping dimming signal Vcp, the dimming control signal Vs, the feedback signal FB, and the output signal Vc are all voltage signals.

It can be seen from the above description that the dimming control method according to the embodiment of the present invention includes: receiving a dimming signal from the outside through a dimming signal input port; generating a clamped dimming signal by clamping the dimming signal; The dimming signal is filtered to generate a dimming control signal; and an output signal for controlling the brightness of the light source is generated by adjusting the magnitude of the feedback signal capable of reflecting the brightness of the light source according to the magnitude of the dimming control signal.

Other aspects of the dimming control method according to the embodiment of the present invention are the same as or similar to the corresponding aspects of the dimming control circuit described above with reference to FIG. 2 to FIG. 7 , so they are not repeated here.

The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. For example, the algorithms described in particular embodiments may be modified without departing from the basic spirit of the invention in system architecture. Accordingly, the present embodiments are to be considered in all respects as illustrative and not restrictive, the scope of the present invention is defined by the appended claims rather than the foregoing description, and the meanings and equivalents falling within the claims All changes within the scope of the invention are thus included in the scope of the present invention.

200: Dimming control circuit

206: Dimming amplifier

204: Filter circuit

202: Voltage clamping circuit

C21: Capacitor

DIM: Dimming signal input port

FB: feedback signal

R21, R22: Resistor

Vc: output signal

Vcp: clamp dimming signal

VH: clamp voltage

Vs: Dimming control signal

Claims (9)

A dimming control circuit, comprising: a dimming signal input port, operable to receive a dimming signal from outside; a voltage clamping circuit, operable to generate a clamped dimming signal by clamping the dimming signal, including a first amplifier and a first adjustment transistor, the first amplifier is operable to control the first adjustment transistor to be in a conductive state when the dimming signal is higher than a clamp voltage, so that the clamp dimming a signal equal to the clamping voltage; a filter circuit operable to generate a dimming control signal by filtering the clamped dimming signal; and a dimming amplifier operable to generate a dimming control signal according to the magnitude of the dimming control signal The magnitude of the feedback signal capable of reflecting the brightness of the light source is adjusted to generate an output signal for controlling the brightness of the light source. The dimming control circuit of claim 1, wherein the first amplifier is further operable to control the first adjustment transistor to be in an off state when the dimming signal is not higher than the clamping voltage , so that the clamped dimming signal is equal to the dimming signal. The dimming control circuit according to claim 2, wherein the voltage clamping circuit comprises a first voltage comparator, a buffer amplifier, and a switch, and a positive input terminal of the buffer amplifier is connected to the clamping voltage, so The inverting input terminal of the buffer amplifier is connected to the output terminal, and the voltage comparator is operable to control the switch to be connected to the output terminal of the buffer amplifier when the dimming signal is higher than the clamping voltage, so that The clamp dimming signal is equal to the clamp voltage. The dimming control circuit of claim 3, wherein the first voltage comparator is further operable to control the switch and the dimming signal when the dimming signal is not higher than the clamping voltage The input port is connected so that the clamped dimming signal is equal to the dimming signal. The dimming control circuit of claim 1, wherein the filter circuit is an RC filter circuit. The dimming control circuit according to claim 1, wherein the filter circuit is realized by the own characteristics of the dimming amplifier and the compensation capacitance. The dimming control circuit of any one of claims 1 to 6, further comprising: a low level control circuit operable to dim the clamped dimming signal when the clamped dimming signal is lower than a reference level pulled down to 0V. The dimming control circuit of claim 7, wherein the low-level control circuit includes a second voltage comparator and a second trim transistor, the second voltage comparator operable to dim at the clamp When the signal is lower than the reference level, the second adjustment transistor is controlled to be turned on, so that the clamped dimming signal is pulled down to 0V by the second adjustment transistor. A dimming control method, comprising: receiving a dimming signal from the outside through a dimming signal input port; generating a clamping dimming signal by clamping the dimming signal, and when the dimming signal is higher than a clamping voltage , making the clamping dimming signal equal to the clamping voltage; generating a dimming control signal by filtering the clamping dimming signal; The magnitude of the brightness feedback signal is used to generate an output signal for controlling the brightness of the light source.

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