CN103476176A - Backlight drive circuit and television - Google Patents
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Abstract
The invention provides a backlight drive circuit which comprises a backlight power supply circuit, a current sampling circuit, a switching circuit and a constant-current control circuit. The backlight power supply circuit provides voltages needed in working to backlight loads according to received pulse drive signals. The current sampling circuit is used for carrying out sampling on the working currents of the backlight loads. The switching circuit is arranged on negative side lines of the backlight loads, and is used for controlling the switching on or off of the negative side lines of the backlight loads. The constant-current control circuit is connected to the current sampling circuit and the switching circuit, and is used for controlling the duty ratio of the switching circuit in a conducting state according to the intensity of the working currents of the backlight loads collected by the current sampling circuit, so that the numerical value of the average working current of the backlight loads is made to be equal to a preset current threshold. The invention further provides a television. Through the technical scheme, the constant-current control over the backlight loads can be achieved.
Description
Technical field
The present invention relates to the backlight drive technical field, in particular to a kind of backlight source driving circuit and a kind of television set.
Background technology
In order to simplify circuit structure, take full advantage of existing circuit, when having proposed by the load of LLC drives backlight in correlation technique, also for driving the peripheral hardwares such as mainboard, sound accompaniment.
As shown in Figure 1A, in correlation technique for realizing a kind of circuit structure of above-mentioned purpose, this circuit comprises: LLC supply convertor 102, (BOOST) booster circuit 104A, backlight load 106, light adjusting circuit 108 etc.; As shown in Figure 1B, in correlation technique for realizing the another kind of circuit structure of above-mentioned purpose, this circuit comprises: LLC supply convertor 102, (BUCK) reduction voltage circuit 104B, backlight load 106, light adjusting circuit 108 etc.
Because LLC supply convertor 102 need to provide the stable voltages such as 12V, 18V for mainboard, sound accompaniment etc., while making it support or oppose at the same time the light source load output voltage, this voltage is very unstable, can't guarantee the constant current of backlight load is driven, must can drive for the constant current to the backlight load through the conversion of the DC-DC as BOOST booster circuit 104A or BUCK reduction voltage circuit 104B, make the more load of whole circuit, and manufacturing cost is high, be unfavorable for actual industrial production.
Therefore, as more simple circuit structure how, realize the constant current of backlight load is driven, become technical problem urgently to be resolved hurrily at present.
Summary of the invention
In order one of to solve the problems of the technologies described above at least, the invention provides a kind of backlight driver technology, can realize the constant current of backlight load is controlled.
In view of this, the invention provides a kind of backlight source driving circuit, comprise: the backlight power supply circuits, be connected to and comprise a LED string in parallel and the backlight load of the 2nd LED string, according to the first pulse drive signal received and the second pulse drive signal, control the described LED string of alternate conduction and described the 2nd LED string, and the difference of the duty ratio of described the first pulse drive signal and described the second pulse drive signal is less than or equal to preset difference value, current sampling circuit, sampled for the operating current to described backlight load, switching circuit, be arranged on the negative terminal circuit of described backlight load, for the closed of the negative terminal circuit of controlling described backlight load or disconnect, constant-current control circuit, be connected to described current sampling circuit and described switching circuit, and described constant-current control circuit also receives the first homogenous frequency signal and the second homogenous frequency signal that corresponds respectively to described the first pulse drive signal and described the second pulse drive signal, and respectively at described the first homogenous frequency signal or described the second homogenous frequency signal between high period, the intensity of the operating current of the described backlight load collected according to described current sampling circuit, control the duty ratio of described switching circuit in conducting state, numerical value with the average operating current that makes respectively a described LED string and described the 2nd LED go here and there equals default current threshold.
In this technical scheme, the difference of the duty ratio by making the first pulse drive signal and the second pulse drive signal is less than or equal to preset difference value, makes to a LED string and the 2nd LED and goes here and there the electric current balance as much as possible of power supply signal of corresponding output.In the ideal situation, the difference of duty ratio is zero; And exist less difference when (being less than or equal to preset difference value) when the difference of duty ratio, can be by controlling the conducting duty ratio of backlight load, make up to a certain extent the problem that the duty ratio difference of two pulse drive signals causes, realize current balance type.
By the operating current to the backlight load, sampled, and the intensity based on its operating current comes conducting or the shutoff of control switch circuit, the duty ratio with the control switch circuit in conducting state, and then make the conducting of backlight load or turn-off controlled.By the conducting duty ratio to the backlight load, controlled, make the average operating current of backlight load controlled, and be controlled in the current threshold that equals all the time default, thereby realized the constant current of the operating current of backlight load is controlled, can also realize above-mentioned for the current balance type adjustment between two LED strings.Certainly, in actual application, the average operating current of backlight load may equal default current threshold, also may there is small difference, such as being slightly less than default current threshold or being slightly larger than default current threshold, but belong to acceptable error range, still can guarantee the current balance type of two LED strings.
Sampling by the operating current to the backlight load, to control the average operating current of backlight load, thereby without adopting complicated booster circuit or reducing circuit, and only adopt switching circuit, can realize the constant current of backlight load is controlled, contribute to simplify circuit structure, promote the reliability of circuit.
By introducing the first pulse drive signal and homogenous frequency signal corresponding to the second pulse drive signal, make within the time period that a LED goes here and there and the 2nd LED string is worked respectively, can carry out Duty ratio control to both respectively, to regulate average operating current, realize constant current control.Such as when the first pulse drive signal is high level, suppose a LED string job,, by introducing the first homogenous frequency signal corresponding to the first pulse drive signal, making at this first pulse drive signal is between high period, can be controlled the operating current of a LED string.Owing to carrying out the electric current adjusting during high level at the first homogenous frequency signal or the second homogenous frequency signal, thereby when the difference of the duty ratio of the first pulse drive signal and the second pulse drive signal is excessive, still take at the first pulse drive signal as between high period, operating current to a LED string is controlled as example, may make before the average current of a LED string not yet reaches required current values, the first pulse drive signal transfers low level to by high level, thereby cause realizing the constant current control to a LED string, also can't realize the current balance of two LED strings.
In addition, the intensity of the operating current obtained according to sampling (being the size of current values), realization has much the mode of the control of the conducting duty ratio of LED string, such as the direct intensity of the operating current based on real-time is controlled, or the calculating of the average current based on in a period of time is controlled etc.Particularly, for the mode of calculating average current, after can carrying out integration by the difference to operating current and predetermined current threshold value, in conjunction with the first homogenous frequency signal or the second homogenous frequency signal, generate the pulse-width signal for the control switch circuit.
According to another aspect of the invention, also propose a kind of television set, comprised the backlight source driving circuit proposed in technique scheme.
By technique scheme, can simplify circuit structure, when reducing production costs, realize the constant current of backlight load is controlled.
The accompanying drawing explanation
Figure 1A shows in correlation technique the schematic diagram of the backlight source driving circuit that has adopted booster circuit;
Figure 1B shows in correlation technique the schematic diagram of the backlight source driving circuit that has adopted reduction voltage circuit;
Fig. 2 A shows the structural representation of backlight source driving circuit according to an embodiment of the invention;
Fig. 2 B shows the structural representation of realizing the backlight source driving circuit that the equal constant current of positive-negative half-cycle is controlled according to an embodiment of the invention;
Fig. 2 C shows the structural representation of the controlled backlight source driving circuit of the equal constant current of realized positive-negative half-cycle according to another embodiment of the invention;
Fig. 2 D shows the structural representation of backlight source driving circuit according to another embodiment of the invention;
Fig. 3 A shows the schematic diagram of backlight source driving circuit according to an embodiment of the invention;
Fig. 3 B shows the schematic diagram of backlight source driving circuit according to another embodiment of the invention.
Embodiment
In order more clearly to understand above-mentioned purpose of the present invention, feature and advantage, below in conjunction with the drawings and specific embodiments, the present invention is further described in detail.It should be noted that, in the situation that do not conflict, the application's embodiment and the feature in embodiment can combine mutually.
Set forth in the following description a lot of details so that fully understand the present invention, still, the present invention can also adopt other to be different from other modes described here and implement, and therefore, the present invention is not limited to the restriction of following public specific embodiment.
Fig. 2 A shows the structural representation of backlight source driving circuit according to an embodiment of the invention.
As shown in Figure 2 A, backlight source driving circuit according to an embodiment of the invention comprises:
Backlight power supply circuits 202, under the driving of the pulse drive signal received, be converted to the required voltage of backlight load 204 work by the ac supply signal received.Wherein, ac supply signal can be from the power frequency supply (not shown), through rectifying and wave-filtering (not shown), PFC(Power Factor Correct, power factor correction) after presetting (not shown), export backlight power supply circuits 202 to.
Current sampling circuit 206, sampled for the operating current to described backlight load 204.Particularly, the connected mode of current sampling circuit 206 has a variety of, such as being connected between switching circuit 208 and ground, also can be connected between the negative electrode of switching circuit 208 and LED string 204A and the 2nd LED string 204B, can also be connected to the anode-side of a LED string 204A and the 2nd LED string 204B etc.
Switching circuit 208, for the closed of the negative terminal circuit of controlling described backlight load 204 or disconnect.Particularly, switching circuit 208 can be arranged between current sampling circuit 206 and backlight load 204, i.e. situation as shown in Figure 2 A; Also switching circuit 208 can be arranged between current sampling circuit 206 and ground, current sampling circuit 206 and backlight load 204 are directly joined, switching circuit 208 can be controlled the closed or disconnection of the negative terminal circuit of backlight load 204 equally.
Constant-current control circuit 210, be connected to current sampling circuit 206 and switching circuit 208.On the one hand, constant-current control circuit 210 receives the first homogenous frequency signal and the second homogenous frequency signal that corresponds respectively to the first pulse drive signal and the second pulse drive signal; On the other hand, respectively at the first homogenous frequency signal or the second homogenous frequency signal between high period, the described backlight load 204(collected according to described current sampling circuit 206 at one time in, the intensity of an operating current only LED string 204A or the 2nd LED string 204B conducting in running order), control the duty ratio of described switching circuit 208 in conducting state, so that the numerical value of the average operating current of described backlight load 204 is less than or equal to default current threshold.
One, the constant current of backlight load is controlled
In circuit structure as shown in Figure 2 A, the application has adopted the operating current of backlight load 204 has been sampled, and the intensity based on its operating current is come conducting or the shutoff of control switch circuit 208, duty ratio with control switch circuit 208 in conducting state, and then make the conducting of backlight load 204 or turn-off controlled.And controlled by the conducting duty ratio to backlight load 204, make the average operating current of backlight load 204 controlled, and be controlled in the current threshold that equals all the time default, thereby realized the constant current control to the operating current of backlight load 204.Certainly, in actual application, the average operating current of backlight load 204 may equal default current threshold, also may there is small difference, such as being slightly less than default current threshold or being slightly larger than default current threshold, but belong to acceptable error range, still can guarantee the current balance type of two LED strings.So, the foregoing circuit structure can be by the sampling of the operating current to backlight load 204, to control the average operating current of backlight load 204, thereby without adopting complicated booster circuit or reducing circuit, and only adopt switching circuit 208, can realize the constant current of backlight load 204 is controlled, contribute to simplify circuit structure, promote the reliability of circuit.
Particularly, backlight load 204 comprises LED lamp group, and such as a LED string 204A who is connected in parallel and the 2nd LED string 204B, each LED string can comprise the LED lamp bar of a LED lamp bar or a plurality of serial connections; Corresponding, the pulse drive signal that backlight power supply circuits 202 receive also can comprise the first pulse drive signal and the second pulse drive signal, this first pulse drive signal and the second pulse drive signal driven backlight power supply circuits 202, make backlight power supply circuits 202 alternately to power to a LED string 204A and the 2nd LED string 204B.
In control procedure, the duty ratio of the first pulse drive signal and the second pulse drive signal should be equal as far as possible, thereby make to a LED string and the 2nd LED, goes here and there the electric current balance as much as possible of power supply signal of corresponding output; When the difference of duty ratio exists less difference when (being less than or equal to preset difference value), can pass through current sampling circuit 206, switching circuit 208 and constant-current control circuit 210 etc. and control the conducting duty ratio of a LED string and the 2nd LED string, make up to a certain extent the problem that the duty ratio difference of two pulse drive signals causes, realize current balance type.
Simultaneously, " the first pulse drive signal " in description, " the first homogenous frequency signal ", " a LED string 204A ", do not represent its corresponding relation each other; Except in literary composition being clearly " corresponding to the first homogenous frequency signal of the first pulse drive signal ", make and have corresponding relation between the two, in other situations, should be understood to only for distinguishing equal a plurality of identical things, as " a LED string 204A " and " the 2nd LED string 204B ".Therefore, except non-designated structure and the annexation of circuit, can not think as necessarily by the first pulse drive signal or the first homogenous frequency signal, driven a LED string 204A etc.
Suppose when the first pulse drive signal is high level, in the positive half period of whole power-up period, a LED string 204A conducting; When the second pulse drive signal is high level, in the negative half-cycle of whole power-up period, the 2nd LED string 204B conducting.Thereby, when the first pulse drive signal and the second pulse drive signal are alternately exported high level, make a LED string 204A and the 2nd LED string 204B alternate conduction.
Although, for backlight load 204, whole power-up period is an integral body; But for a LED string 204A and the 2nd LED string 204B, positive half period wherein and negative half-cycle are but relatively independent respectively.Wherein, when in positive half period, a LED string 204A conducting, the operating current that current sampling circuit 206 collects i.e. the first operating current of a LED string 204A; When in negative half-cycle, the 2nd LED string 204B conducting, the operating current that current sampling circuit 206 collects i.e. the second operating current of the 2nd LED string 204B.
In order to make a LED string 204A and the 2nd LED string 204B can both realize the constant current control of electric current, can be calculated respectively by constant-current control circuit 210 the average operating current of a LED string 204A and the 2nd LED string 204B at positive half period and negative half-cycle, use the first operating current to calculate first average current of a LED string 204A in positive half period, use the second operating current to calculate second average current of the 2nd LED string 204B in negative half-cycle, thereby realize all controlled to the positive-negative half-cycle of backlight load 204.
Particularly, for the mode of calculating average current, after can carrying out integration by the difference to operating current and predetermined current threshold value, in conjunction with the first homogenous frequency signal or the second homogenous frequency signal, generate the pulse-width signal for the control switch circuit.Certainly, also can not adopt the mode of calculating average operating current, but directly the intensity of the operating current based on real-time is controlled, although precision is relatively low, control mode and algorithm are more simple.
All controlled in order to realize the positive-negative half-cycle of backlight load 204, need to be monitored the first pulse drive signal and the second pulse drive signal, specifically can adopt various ways, such as:
Mode one
As shown in Fig. 2 B, constant-current control circuit 210 directly, under the driving of the first pulse drive signal and the second pulse drive signal, is realized a LED string 204A and the 2nd LED string 204B are controlled in the constant current of positive-negative half-cycle.Particularly, the first pulse drive signal and the second pulse drive signal can be accessed respectively to optical coupling isolation circuit 212, again by optical coupling isolation circuit 212 under the driven of the first pulse drive signal and the second pulse drive signal, to corresponding the first homogenous frequency signal and the second homogenous frequency signal of constant-current control circuit 210 output.
Mode two
As shown in Figure 2 C, constant-current control circuit 210 is not directly monitored the first pulse drive signal and the second pulse drive signal, but obtains the homogenous frequency signal corresponding to pulse drive signal.Particularly, because backlight power supply circuits 202 are worked under the driving of the first pulse drive signal and the second pulse drive signal, thereby the first homogenous frequency signal and the second homogenous frequency signal that can be exported corresponding to the first pulse drive signal and the second pulse drive signal by backlight power supply circuits 202, and realize the driven to constant-current control circuit 210 by this first homogenous frequency signal and the second homogenous frequency signal.
By the way, constant-current control circuit 210 is under the driving of the first homogenous frequency signal corresponding to the first pulse drive signal and the second pulse drive signal and the second homogenous frequency signal, alternately calculate the first average operating current and the second average operating current of a LED string 204A and the 2nd LED string 204B, thereby generate the corresponding pulse-width signal for control switch circuit 208, make a LED string 204A or the 2nd LED string 204B controlled in the duty ratio of conducting state, realized respectively the constant current of a LED string 204A and the 2nd LED string 204B is controlled.
In addition, because technique scheme is known, owing to having introduced the first pulse drive signal and homogenous frequency signal corresponding to the second pulse drive signal, make and must carry out the electric current adjusting during high level at the first homogenous frequency signal or the second homogenous frequency signal, thereby when the difference of the duty ratio of the first pulse drive signal and the second pulse drive signal is excessive, take at the first pulse drive signal as between high period, operating current to a LED string 204A is controlled as example, may make before the average current of a LED string 204A not yet reaches required current values, the first pulse drive signal transfers low level to by high level, thereby cause realizing the constant current control to a LED string 204A, also can't realize the current balance of two LED strings.So the duty ratio of the first pulse drive signal and the second pulse drive signal should be equal as far as possible, or at least should be less than or equal to preset difference value, otherwise can't make up by other means, cause the electric current of two LED strings can't realize equilibrium.
On the basis of the embodiment based on shown in Fig. 2 A-2C, in order further to realize the current balance type of a LED string 204A and the 2nd LED string 204B and to realize respectively the constant current of a LED string 204A and the 2nd LED string 204B is controlled by switching circuit 208, the present invention gives another embodiment shown in Fig. 2 D.
As shown in Figure 2 D, can also add balancing capacitance 216 between backlight power supply circuits 202 and backlight load 204, the characteristic of utilizing it to discharge and recharge, carry out equilibrium to the operating current on a LED string 204A and the 2nd LED string 204B.
In order to make balancing capacitance 216 to work, this technical scheme also comprises Energy Transfer circuit (not indicating in figure), and this Energy Transfer circuit specifically can comprise:
The first power supply branch road 212A, one end is connected to the first output of described backlight power supply circuits 202, the other end is connected to any in a described LED string 204A or described the 2nd LED string 204B, such as this sentences, to be connected to a LED string 204A be example, and export the first power supply signal to a LED string 204A.
The first equalized current circuit 214A, an end is connected to described the first power supply branch road 212A, and the other end is connected to the second output of described backlight power supply circuits 202.
The second power supply branch road 212B, one end is connected to the second output port of described backlight power supply circuits 202, the other end is connected to another in a described LED string 204A or described the 2nd LED string 204B, such as this sentences, to be connected to the 2nd LED string 204B be example, and export the second power supply signal to the 2nd LED string 204B.
The second equalized current circuit 214B, an end is connected to described the second power supply branch road 212B, and the other end is connected to the first output port of described backlight power supply circuits 202.
Pass through foregoing circuit, on the one hand completed the support or oppose transmission of power supply signal of light source load 204 of backlight power supply circuits 202, realized on the other hand the support to balancing capacitance 216, make: during any conducting in a LED string 204A or the 2nd LED string 204B, balancing capacitance 216 realizes charging process; When another LED string conducting, balancing capacitance 216 realizes discharge process.Equate owing to charging and discharging electric weight, thereby realized the current balance type to a LED string 204A and the 2nd LED string 204B.
More specifically, the concrete structure of balancing capacitance 216 can comprise:
1) as shown in Figure 2 D, when the first output, the negative pole that the positive pole of balancing capacitance 216 is connected to backlight power supply circuits 202 is connected to the first power supply branch road 212A, if backlight power supply circuits 202 output the first power supply signals, balancing capacitance 216 chargings, if backlight power supply circuits 202 output the second power supply signals, balancing capacitance 216 electric discharges; (not shown) when the first output, the positive pole that 2) negative pole of balancing capacitance 216 is connected to backlight power supply circuits 202 is connected to the first power supply branch road 212A, if backlight power supply circuits 202 output the second power supply signals, balancing capacitance 216 chargings, if backlight power supply circuits 202 output the first power supply signals, balancing capacitance 216 electric discharges; (not shown) when the second output, the negative pole that 3) positive pole of balancing capacitance 216 is connected to backlight power supply circuits 202 is connected to the second power supply branch road 212B, if backlight power supply circuits 202 output the second power supply signals, balancing capacitance 216 chargings, if backlight power supply circuits 202 output the first power supply signals, balancing capacitance 216 electric discharges; (not shown) when the second output, the positive pole that 4) negative pole of balancing capacitance 216 is connected to backlight power supply circuits 202 is connected to the second power supply branch road 212B, if backlight power supply circuits 202 output the first power supply signals, balancing capacitance 216 chargings, if backlight power supply circuits 202 output the second power supply signals, balancing capacitance 216 electric discharges.
The concrete formation of above-mentioned power supply branch road and equalized current circuit can comprise:
Described the first power supply branch road 212A can consist of the first diode (not shown), and any that the positive pole of described the first diode is connected with the first output of described backlight power supply circuits 202, negative pole and a described LED string 204A or described the 2nd LED go here and there in 204B is connected.
Described the first equalized current circuit 214A can consist of the second diode (not shown), and the positive pole of described the second diode is connected with the negative pole of described the first diode, negative pole is connected with the second output of described backlight power supply circuits 202.
Described the second power supply branch road 212B can consist of the 3rd diode (not shown), and the positive pole of described the 3rd diode is connected with the second output of described backlight power supply circuits 202, negative pole and a described LED string 204A or described the 2nd LED go here and there another in 204B and be connected.
Described the second equalized current circuit 214B can consist of the 4th diode (not shown), and the positive pole of described the 4th diode is connected with the negative pole of described the 3rd diode, negative pole is connected with the first output of described backlight power supply circuits 202.
By four above-mentioned diodes, make the normal execution that can guarantee on the one hand the charge and discharge process of balancing capacitance 216, can realize on the other hand the support or oppose power supply signal of light source load 204 output of backlight power supply circuits 202 is carried out to rectification, contribute to improve the operation stability of system.
In the embodiment as shown in Fig. 2 A-2C, by the operating current to backlight load 204, sampled, and introduce the homogenous frequency signal of the first pulse drive signal and the second pulse drive signal, make in positive-negative half-cycle and can carry out constant current control to a LED string 204A and the 2nd LED string 204B respectively.But owing to by balancing capacitance 216 grades as shown in Figure 2 D, not realizing the balance adjustment of electric current, making need to be by switching circuit 208, constant-current control circuit 210 etc., by the average current to a LED string 204A and the 2nd LED string 204B, controlled respectively, thereby improve both current balance type problems, may cause the amplitude of accommodation of the conducting duty ratio of a LED string 204A and the 2nd LED string 204B larger.
And, in embodiment as shown in Figure 2 D, on the one hand, by adding balancing capacitance 216 device such as grade or circuit, a LED string 204A and the 2nd LED string 204B are carried out to current balance type; On the other hand, by switching circuit 208, constant-current control circuit 210 etc., realize can carrying out constant current control to a LED string 204A and the 2nd LED string 204B respectively in positive-negative half-cycle.Owing to regulating by the current balance type situation of 216 couples of LED string 204A of balancing capacitance and the 2nd LED string 204B in advance, make for switching circuit 208, constant-current control circuit 210 etc., almost only needing consideration the one LED string 204A and the 2nd LED string 204B constant current separately to control gets final product, thereby relatively less to the amplitude of accommodation of its duty ratio, make whole system be not easy, because excessive adjusting causes occurring as problems such as system oscillations, to be conducive to realize the better stability of a system.
Two, drive when a plurality of peripheral hardware
Due to the circuit structure adopted as shown in Fig. 2 A-2D, make this backlight source driving circuit can pass through the detection to the operating current of backlight load 204, realization is controlled the constant current of backlight load 204, thereby those skilled in the art can be understood that: backlight power supply circuits 202 can also provide the power supply (not shown) of 12V, 18V equal-specification simultaneously for peripheral hardwares such as mainboard, sound accompaniments, with simple circuit structure, drive when having realized a plurality of equipment, and all can access good implementation result.
Three, brightness adjustment control
In the technical scheme as shown in Fig. 2 A-2D, by switching circuit 208, realize the closed of backlight load 204 circuit of living in or disconnect control.Similarly, need to use the equipment of backlight for LCDs, liquid crystal TV set etc., also can realize the brightness adjustment control to backlight load 204 by switching circuit 208.
Particularly, can be by constant-current control circuit 210 input light modulation pwm signal (not shown)s, and control switching circuit 208 conductings by constant-current control circuit 210 when the high level, control switching circuit 208 during in low level and turn-off.Certainly, also can adopt other control circuit, such as the adjusting control circuit (not shown), directly switching circuit 208 be controlled.
Therefore, the application is actually a longer brightness adjustment control in the cycle, realize the constant current control cycle of a shorter backlight load 204, and should be when the light modulation pwm signal is high level, realization is controlled the constant current of backlight load 204, when the light modulation pwm signal is low level, directly controls backlight load 204 and disconnect; Be the priority of the priority of brightness adjustment control higher than constant current control.
Below in conjunction with Fig. 3 A and 3B, the concrete structure based on backlight source driving circuit of the present invention and operation principle are elaborated, wherein, Fig. 3 shows the schematic diagram of backlight source driving circuit according to an embodiment of the invention.
One, LLC circuit structure
As shown in Fig. 3 A and 3B, in backlight source driving circuit according to an embodiment of the invention, the backlight power supply circuits 202 that half-bridge drive circuit 302A, resonance select wave circuit 302B to form to be equivalent to shown in Fig. 2 A-2D; Backlight load 304 is equivalent to the backlight load 204 shown in Fig. 2 A-2C or LED string 204A and the 2nd LED string 204B; Current sampling circuit 306 is equivalent to the current sampling circuit 206 shown in Fig. 2 A-2C; Switching circuit is equivalent to the switching circuit 208 shown in Fig. 2 A-2C; Constant-current control circuit 310 is equivalent to the constant-current control circuit 210 shown in Fig. 2 A-2C.
Half-bridge drive circuit 302A mainly comprises: the first switching tube V864 and second switch pipe V865, wherein, the drain electrode of the first switching tube V864 is connected to that external ac power source, source electrode are connected to the drain electrode of second switch pipe V865 and first input end, grid that resonance selects wave circuit 302B are connected to the first pulse drive signal by the input of Dri-H port, and source electrode, source electrode that the drain electrode of second switch pipe V865 is connected to the first switching tube V864 are connected to resonance and select the second input of wave circuit 302B and ground, grid to be connected to the second pulse drive signal by the input of Dri-L port.
Resonance selects wave circuit 302B to comprise: transformer T905(is specially primary coil and the leakage inductance of transformer T905) and resonance capacitor C 919; Wherein, it is the first incoming end of the primary coil of transformer T905 that resonance selects the first input end of wave circuit 302B, it is the second incoming end of the primary coil of transformer T905 that resonance selects the second input of wave circuit 302B, and resonant capacitance C919 can be connected between this second incoming end and ground as shown in Fig. 3 A and 3B, also can be connected between the first incoming end of primary coil of the drain electrode of source electrode as the first switching tube V864, second switch 865 and transformer T905.
By half-bridge drive circuit 302A and resonance, select wave circuit 302 jointly to form the LLC circuit in the application's backlight source driving circuit, or the LLC supply convertor.The LLC circuit is a kind of novel high efficiency half-bridge converter scheme, its duty ratio constant (approach 50%, and leave Dead Time), and the gain that can change by regulating operating frequency loop reaches the purpose of voltage stabilizing or constant current.The LLC circuit can be realized ZVS(Zero Voltage Switch, zero voltage switch in loading range) the efficient switch mode.Because the LLC circuit is the half-bridge structure of both-end excitation, must guarantee the waveform symmetry of positive-negative half-cycle, to reach the requirement of magnetic balance, so the waveform in the positive-negative half-cycle of the first pulse drive signal of Dri-H port and Dri-L port input and the second pulse drive signal is symmetrical, the 50%(that duty ratio is " complementation " approaches 50%; The duty ratio of two signals should be suitable as much as possible, also can be not exclusively equal, but the difference of the duty ratio of two signals can not be excessive, such as being less than or equal to preset difference value).
Wherein, the first switching tube V864 and second switch pipe V865 alternate conduction under the driving of the first pulse drive signal and the second pulse drive signal, duty ratio approaches 50%; And the inductance of transformer T905, leakage inductance and resonance capacitor C 919 participate in resonance, jointly select the sinusoidal fundamental wave in the square wave that half-bridge drive circuit 302A produces, and be coupled to secondary coil by transformer T905; Diode VD939 and diode VD940 alternate conduction are the positive-negative half-cycle current waveform rectification of 12V winding output, for peripheral hardware (as mainboard) provides 12V voltage; Simultaneously, transformer T905 also produces the supply power voltage for the 12V of backlight load 304.
Two, the constant current of backlight load is controlled
When using the required 12V voltage of above-mentioned LLC circuit output mainboard, the required 18V of sound accompaniment etc., while driving backlight load 304 simultaneously: due to only to as the 12V voltage etc. of output mainboard controlled, and make the voltage that exports backlight load 304 to not controlled, so cause the voltage of LED906 and LED907 can produce fluctuation, if directly drive backlight load 304, the electric current of LED906 and LED907 is not controlled, can not realize constant current control.
Thereby, the application controls the constant current of backlight load 304 in order to realize, proposed: the sampling of the operating current by 306 pairs of backlight loads 304 of current sampling circuit, constant-current control circuit 310 calculates the average operating current of backlight load 304, and by the duty ratio of control switch circuit 308 in conducting state, realization is controlled the constant current of backlight load 304, makes its average operating current remain predetermined current.
Wherein, the current sampling circuit shown in Fig. 3 306 comprises that sampling resistor R921, switching circuit 308 comprise that the 3rd switching tube V905, constant-current control circuit 310 comprise control chip N907.
The course of work of above-mentioned backlight source driving circuit is as follows:
When the second pulse drive signal that the first pulse drive signal of inputting when the Dri-H port is high level, the input of Dri-L port is low level, suppose an above-mentioned port output high level, the another port output low level of transformer T905, current direction is: an above-mentioned port-first diode VD935-LED906-the 3rd switching tube V905-sampling resistor R921 of transformer T905, and the above-mentioned another port of first diode VD935-second balancing capacitance C907-the 4th diode VD938-the first balancing capacitance C920-transformer T905.
When the first pulse drive signal that the second pulse drive signal of inputting when the Dri-L port is high level, the input of Dri-H port is low level, suppose an above-mentioned port output low level, the another port output high level of transformer T905, current direction is: above-mentioned another port-first balancing capacitance C920-the 3rd diode VD937-LED907-the 3rd switching tube V905-sampling resistor R921 of transformer T905, and the above-mentioned port of the 3rd diode VD937-the 3rd balancing capacitance C908-the second diode VD936-transformer T905.
Due to when the positive-negative half-cycle, only LED906 or LED907 conducting, such as take the first pulse drive signal of Dri-H input, as the second pulse drive signal of positive half period, Dri-L input, be negative half-cycle during as high level during as high level, when positive half period, what sampling resistor R921 collected is the operating current of LED906, and what constant current control chip N907 realized is that the constant current of LED906 is controlled; When negative half-cycle, what sampling resistor R921 collected is the operating current of LED907, and what constant current control chip N907 realized is that the constant current of LED907 is controlled.
So, all controlled in order to realize positive-negative half-cycle, need to by constant current control chip N907, the first pulse drive signal and the second pulse drive signal be monitored by constant-current control circuit 310, particularly, such as:
Under a kind of mode, Dri-H port and Dri-L port are coupled to the input of constant current control chip N907, such as the first pulse drive signal and the second pulse drive signal are inputted to optical coupler, and the first homogenous frequency signal that the correspondence coupling is obtained and the second homogenous frequency signal input constant current control chip N907, thereby realize the monitoring (not shown) to the first pulse drive signal and the second pulse drive signal.
Under another kind of mode, as shown in Fig. 3 A and 3B, by transformer T905 according to the first pulse drive signal and the second pulse drive signal, respectively secondary coil export corresponding homogenous frequency signal as D1 and D2 port, and input to the input of constant current control chip N907.
Under the driving at the first pulse drive signal and the second pulse drive signal, realization is controlled the constant current of backlight load 304, make it possible to realize respectively LED906 and LED907 being carried out to constant current control in positive-negative half-cycle, guarantee the to flow through electric current of transformer T905 in positive-negative half-cycle is identical, has guaranteed the magnetic-reset of transformer T905.
Three, electric current, the balance of voltage are controlled
In order to make transformer T905 under the driving of the first pulse drive signal and the second pulse drive signal, can make transformer T905 magnetic-reset, avoid occurring magnetic bias, need to guarantee the current balance type in positive-negative half-cycle.In order to realize current balance type, can adopt following manner:
(1), in the embodiment as shown in Fig. 3 A and 3B, by the duty ratio to the first pulse drive signal and the second pulse drive signal, controlled, to guarantee current balance type.
Particularly, should make as much as possible two to drive the duty ratio of signals to equate, thereby make to the electric current of the power supply signal of LED906 and the corresponding output of LED907 balance as much as possible; When the difference of duty ratio exists less difference when (being less than or equal to preset difference value), can pass through following manner (2) and/or (3), make up to a certain extent the problem that the duty ratio difference of two pulse drive signals causes, realize current balance type.
(2), in the embodiment as shown in Fig. 3 A and 3B, can also, by the control of the conducting duty ratio to LED906 and LED907, realize current balance type control.
Particularly, after by sampling resistor R921, the operating current of LED906 or LED907 being sampled, by constant current control chip N907 between the high period corresponding to the first pulse drive signal or the second pulse drive signal, calculate and export corresponding pulse-width signal, make the conducting duty ratio of the 3rd switching tube V905 is controlled.Controlled by the real work electric current to LED906 and LED907 respectively, can either be controlled the constant current of single LED906 and LED907, can be controlled both current balance types again.
(3) as shown in Figure 3 B,, on the basis of being controlled in the conducting duty ratio for LED906 and LED907, can also realize by other means current balance type.
Particularly, by the first diode VD935, the second diode VD936, the 3rd diode VD937 and the 4th diode VD938, form required circuit, and by balancing capacitance C920 specific implementation current balance type.Wherein:
The first diode VD935, the positive pole of described the first diode VD935 is connected with an output of the secondary coil of described transformer T905, negative pole is connected with the input of LED906; The second diode VD936, the positive pole of described the second diode VD936 is connected with the negative pole of the 3rd diode VD937, negative pole is connected with the positive pole of described the first diode VD935; The 3rd diode VD937, the positive pole of described the 3rd diode VD937 is connected with another output of the secondary coil of described transformer T905, negative pole is connected with the input of LED907; The 4th diode VD938, the positive pole of described the 4th diode VD938 is connected with the negative pole of the first diode VD935, negative pole is connected with the positive pole of described the 3rd diode VD937.
Balancing capacitance C920, the positive pole of described balancing capacitance C920 with describedly be connected, negative pole is connected (not shown) with the positive pole of the first diode VD935, or the positive pole of described balancing capacitance C920 is connected with described another output of the secondary coil of described transformer T905, negative pole is connected (as shown in Figure 3) with the negative pole of the 4th diode VD938.
The connected mode of balancing capacitance C920 has a lot, such as: 1) as shown in Figure 3 B, when above-mentioned another output, the negative pole that the positive pole of balancing capacitance C920 is connected to the secondary coil of transformer T905 is connected to the negative pole of anodal and the 4th diode VD938 of the 3rd diode VD937, if LED907 conducting, balancing capacitance C920 charging, if the LED906 conducting, balancing capacitance C920 electric discharge; (not shown) when above-mentioned another output, the positive pole that 2) negative pole of balancing capacitance C920 is connected to the secondary coil of transformer T905 is connected to the negative pole of anodal and the 4th diode VD938 of the 3rd diode VD937, if LED906 conducting, balancing capacitance C920 charging, if the LED907 conducting, balancing capacitance C920 electric discharge; (not shown) when an above-mentioned output, the negative pole that 3) positive pole of balancing capacitance C920 is connected to the secondary coil of transformer T905 is connected to the negative pole of anodal and the second diode VD936 of the first diode VD935, if LED906 conducting, balancing capacitance C920 charging, if the LED907 conducting, balancing capacitance C920 electric discharge; (not shown) when an above-mentioned output, the positive pole that 4) negative pole of balancing capacitance C920 is connected to the secondary coil of transformer T905 is connected to the negative pole of anodal and the second diode VD936 of the first diode VD935, if LED907 conducting, balancing capacitance C920 charging, if the LED906 conducting, balancing capacitance C920 electric discharge.
Can also comprise filter circuit in foregoing circuit, specifically comprise the first capacitor C 907 and the second capacitor C 908, wherein, the first capacitor C 907 is connected between the negative pole and ground of the first diode VD935, and the second capacitor C 908 is connected between the negative pole and ground of the 3rd diode VD937.
Particularly, the situation of below take as shown in Figure 3 B is example, and the current balance type principle in situation (3) is elaborated:
When the first pulse drive signal is that high level, the second pulse drive signal are while being low level, the first switching tube V864 conducting, second switch pipe V865 cut-off, an above-mentioned side of the second coil side of transformer T905 for just, opposite side is for negative (on just lower negative), supposes that its voltage is that V1, electric current are I1; The break-over of device such as the first diode VD935, and the first capacitor C 907 chargings, upper just lower negative, balancing capacitance C920 charging, the left negative right side just, suppose that be T1 conduction time.
When the first pulse drive signal is that low level, the second pulse drive signal are while being high level, the first switching tube V864 cut-off, second switch pipe V865 conducting, an above-mentioned side of the second coil side of transformer T905 is just (under upper bearing just) for negative, opposite side, supposes that its voltage is that V2, electric current are I2; The break-over of device such as the 3rd diode VD937, and the second capacitor C 908 chargings, upper just lower negative, balancing capacitance C920 electric discharge, suppose that be T2 conduction time.
The work period of supposing above-mentioned LLC circuit is T, and the electric current of LED906 is
the electric current of LED907 is
Due to the electric quantity balancing discharged and recharged of balancing capacitance C920, thereby I906=I907; And when the first diode VD935 conducting, V1-V
c920=V
c907, when the 3rd diode VD937 conducting, V2+V
c920=V
c908; And because the duty ratio of the first switching tube V864 in half-bridge drive circuit 302A and second switch pipe V865 conducting is 50%, make V1=V2, so:
therefore, when the operating voltage of LED906 and LED907 there are differences, balancing capacitance C920 can either regulate the direct current (DC) bias of himself automatically, again can be so that the weber of the second coil side of transformer T905 be worth balance.And the electric weight discharged and recharged of the first balancing capacitance C920 equates, thereby can also make the current balance type of LED906 and LED907 simultaneously.
To sum up, in embodiment as shown in Figure 3A, above-mentioned mode (1) and mode (2) have only been adopted, make when the duty ratio difference of the spread of voltage of inputting LED906 or LED907 and/or the first pulse drive signal and the second pulse drive signal is bigger, may cause the current difference of LED906 and LED907 larger; If only by the Duty ratio control of the 3rd switching tube V905, make at LED906 and LED907 when corresponding positive-negative half-cycle is regulated respectively, both current balance types had both been needed to consider, need again to consider LED906 or LED907 constant current control separately, may cause the duty ratio numerical value that both are regulated to differ larger, such as the duty ratio corresponding to LED906 is 20%, and be 60% corresponding to the duty ratio of LED907, make adjustment process more difficult.
And in embodiment as shown in Figure 3 B, owing to having adopted above-mentioned mode (1), mode (2) and mode (3) simultaneously, at first by balancing capacitance C920 to the electric current that flows into LED906 and LED907 balance as much as possible, and then when the duty ratio of the 3rd switching tube V905 is controlled, in fact only need to consider the constant current problem of LED906 or LED907, make both distinguish corresponding duty ratio very close, such as 40% and 41%, avoided significantly adjusting, make adjustment process more easily realize, system is more stable, difficult vibrates.
Four, brightness adjustment control
In the circuit structure shown in Fig. 3 A and 3B, the LCDs based on using this backlight source driving circuit or the demand of LCD TV, need to carry out brightness adjustment control to the LED lamp bar in backlight load 304.
Particularly, can be by constant-current control circuit 310 input light modulation pwm signal (not shown)s, and control switching circuit 308 conductings by constant-current control circuit 310 when the high level, control switching circuit 308 during in low level and turn-off.Certainly, also can adopt other control circuit, such as the adjusting control circuit (not shown), directly switching circuit 308 be controlled.
Therefore, the application is actually a longer brightness adjustment control in the cycle, realize the constant current control cycle of a shorter backlight load 304, and should be when the light modulation pwm signal is high level, realization is controlled the constant current of backlight load 304, when the light modulation pwm signal is low level, directly controls backlight load 304 and disconnect; Be the priority of the priority of brightness adjustment control higher than constant current control.
Owing to being all by switching circuit 308, as the conducting duty ratio of the 3rd switching tube V905 is controlled, to realize the brightness adjustment control to LED906 and LED907, therefore, based on technical scheme of the present invention, only need to arrange a switching circuit 308, just can realize constant current control and the brightness adjustment control to backlight load 304 simultaneously, greatly simplified circuit structure, contributed to promote circuit reliability, and reduce production costs.
In addition, the application has also proposed a kind of television set that comprises above-mentioned arbitrary technical scheme.
The foregoing is only the preferred embodiments of the present invention, be not limited to the present invention, for a person skilled in the art, the present invention can have various modifications and variations.Within the spirit and principles in the present invention all, any modification of doing, be equal to replacement, improvement etc., within all should being included in protection scope of the present invention.
Claims (10)
1. a backlight source driving circuit, is characterized in that, comprising:
The backlight power supply circuits, be connected to and comprise a LED string in parallel and the backlight load of the 2nd LED string, according to the first pulse drive signal received and the second pulse drive signal, control the described LED string of alternate conduction and described the 2nd LED string, and the difference of the duty ratio of described the first pulse drive signal and described the second pulse drive signal is less than or equal to preset difference value;
Current sampling circuit, sampled for the operating current to described backlight load;
Switching circuit, be arranged on the negative terminal circuit of described backlight load, for the closed of the negative terminal circuit of controlling described backlight load or disconnect;
Constant-current control circuit, be connected to described current sampling circuit and described switching circuit, and described constant-current control circuit also receives the first homogenous frequency signal and the second homogenous frequency signal that corresponds respectively to described the first pulse drive signal and described the second pulse drive signal, and respectively at described the first homogenous frequency signal or described the second homogenous frequency signal between high period, the intensity of the operating current of the described backlight load collected according to described current sampling circuit, control the duty ratio of described switching circuit in conducting state, numerical value with the average operating current that makes respectively a described LED string and described the 2nd LED go here and there equals default current threshold.
2. backlight source driving circuit according to claim 1, is characterized in that, also comprises Energy Transfer circuit and balancing capacitance, and described Energy Transfer circuit comprises:
The first power supply branch road, an end is connected to the first output of described backlight power supply circuits, and the other end is connected to any in a described LED string or described the 2nd LED string, for the string of the LED to connected output the first power supply signal;
The first equalized current circuit, an end is connected to described the first power supply branch road, and the other end is connected to the second output of described backlight power supply circuits;
The second power supply branch road, an end is connected to the second output port of described backlight power supply circuits, and the other end is connected to another in a described LED string or described the 2nd LED string, for the string of the LED to connected output the second power supply signal;
The second equalized current circuit, an end is connected to described the second power supply branch road, and the other end is connected to the first output port of described backlight power supply circuits;
Wherein, described balancing capacitance is arranged on first output and described first of described backlight power supply circuits and powers between branch road, described the second equalized current circuit, or the second output and described second that is arranged on described backlight power supply circuits is powered between branch road, described the first equalized current circuit, for charging when described backlight power supply circuits are exported described the first power supply signal or described the second power supply signal, and when exporting described the second power supply signal or described the first power supply signal, described backlight power supply circuits discharge.
3. backlight source driving circuit according to claim 2, is characterized in that,
Described first power supply route the first diode forms, and the positive pole of described the first diode is connected with the first output of described backlight power supply circuits, negative pole is connected with any during a described LED string or described the 2nd LED go here and there;
Described the first equalized current circuit consists of the second diode, and the positive pole of described the second diode is connected with the negative pole of described the first diode, negative pole is connected with the second output of described backlight power supply circuits;
Described the second power supply route the 3rd diode forms, and the positive pole of described the 3rd diode is connected with the second output of described backlight power supply circuits, negative pole is connected with another during a described LED string or described the 2nd LED go here and there;
Described the second equalized current circuit consists of the 4th diode, and the positive pole of described the 4th diode is connected with the negative pole of described the 3rd diode, negative pole is connected with the first output of described backlight power supply circuits.
4. backlight source driving circuit according to claim 3, is characterized in that, also comprises filter circuit, and described filter circuit comprises:
The first electric capacity, the positive pole of described the first electric capacity is connected to negative pole, the minus earth of described the first diode;
The second electric capacity, the positive pole of described the second electric capacity is connected to negative pole, the minus earth of described the 3rd diode.
5. backlight source driving circuit according to claim 1, is characterized in that, described backlight power supply circuits comprise the LLC supply convertor, and described LLC supply convertor comprises:
Half-bridge drive circuit, the drain electrode of the first switching tube in described half-bridge drive circuit is connected to the external communication electricity, source electrode is connected to the first incoming end of the primary coil of transformer, grid accesses described the first pulse drive signal, the drain electrode of the second switch pipe of described half-bridge drive circuit is connected to the first incoming end of the primary coil of described transformer, source electrode is connected to the second incoming end and the ground of the primary coil of described transformer, grid accesses described the second pulse drive signal, wherein, described the first switching tube and described second switch pipe alternate conduction under the driving of described the first pulse drive signal and described the second pulse drive signal, described external communication electricity is converted to square-wave signal to be exported,
Resonance selects wave circuit, the primary coil that comprises described transformer, the leakage inductance of described transformer and resonant capacitance, for selecting the sinusoidal fundamental wave of the square-wave signal produced by described half-bridge drive circuit, and be coupled to the secondary coil of described transformer, and the first output of the secondary coil of described transformer is the first output of described backlight power supply circuits, the second output of the secondary coil of described transformer is the second output of described backlight power supply circuits, wherein, described resonant capacitance is arranged between first incoming end of primary coil of the drain electrode of the source electrode of described the first switching tube and described second switch pipe and described transformer, or be arranged between second incoming end and ground of primary coil of described transformer.
6. backlight source driving circuit according to claim 5, it is characterized in that, described constant-current control circuit is connected to the 3rd output and the 4th output of the secondary coil of described transformer, to obtain respectively described the first homogenous frequency signal and described the second homogenous frequency signal.
7. backlight source driving circuit according to claim 1, it is characterized in that, described constant-current control circuit is connected to optical coupler, and receive described optical coupler according to described the first pulse drive signal and described the second pulse drive signal, described the first homogenous frequency signal and described the second homogenous frequency signal that coupling obtains.
8. according to the described backlight source driving circuit of any one in claim 1 to 7, it is characterized in that, described backlight power supply circuits also for:
According to the pulse drive signal received, to the miscellaneous part except described backlight load in described backlight source driving circuit corresponding device, provide work required voltage.
9. according to the described backlight source driving circuit of any one in claim 1 to 7, it is characterized in that, also comprise:
Light adjusting circuit, be connected to described switching circuit, for the pulse-width signal according to receiving, controls the duty ratio of described switching circuit in conducting state;
Wherein, when described constant-current control circuit is controlled described switching circuit in conducting state at described light adjusting circuit, carry out the constant current of described backlight load is controlled.
10. a television set, is characterized in that, comprises backlight source driving circuit as claimed in any one of claims 1-9 wherein.
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| CN105096840A (en) * | 2015-08-11 | 2015-11-25 | 京东方科技集团股份有限公司 | Backlight driving circuit, backlight driving method and display device |
| CN107086026A (en) * | 2017-04-28 | 2017-08-22 | 康佳集团股份有限公司 | A kind of constant-current circuit and television set of driving LED backlight |
| CN107086026B (en) * | 2017-04-28 | 2019-11-08 | 康佳集团股份有限公司 | A kind of constant-current circuit and television set driving LED backlight |
| WO2021139093A1 (en) * | 2020-01-08 | 2021-07-15 | 毛昭祺 | Multi-path resonant conversion circuit and multi-path output control method based on same |
| CN114708822A (en) * | 2022-04-12 | 2022-07-05 | 长沙硕博电子科技股份有限公司 | LED screen backlight constant-current short-circuit-prevention control system and short-circuit-prevention fault control method |
| CN114708822B (en) * | 2022-04-12 | 2024-06-18 | 长沙硕博电子科技股份有限公司 | LED screen backlight constant-current short-circuit prevention control system and short-circuit failure prevention control method |
| CN119562407A (en) * | 2025-02-05 | 2025-03-04 | 合肥为国半导体有限公司 | LED driver chip, LED control circuit, backlight module and display device |
| CN119562407B (en) * | 2025-02-05 | 2025-05-02 | 合肥为国半导体有限公司 | LED driving chip, LED control circuit, backlight module and display device |
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Effective date of registration: 20160629 Address after: 529000, Guangdong, Jiangmen province advanced manufacturing Sand River Demonstration Park, Hisense Road, No. 8, B District, 1 blocks Patentee after: GUANGDONG HISENSE ELECTRONIC CO., LTD. Address before: 266555 Qingdao economic and Technological Development Zone, Shandong, Hong Kong Road, No. 218 Patentee before: Qingdao Hisense Electric Co., Ltd. |