Summary of the invention
For this reason, technical matters to be solved by this invention is: a kind of circuit and driving method thereof that uses chip microcontroller multichannel backlight drive is provided, makes multichannel backlight drive circuit simple in structure, and flexible configuration, low cost of manufacture, safe.
So, the invention provides a kind of circuit that uses chip microcontroller multichannel backlight drive, comprise: flyback topology constant voltage output unit and MCU control module, wherein, MCU control module comprises: MCU chip, LED lamp string and with the LED lamp dimmer switch pipe connecing of contacting, dimmer switch pipe is connected with MCU chip by current sense resistor, flyback topology output unit output voltage is to LED lamp string, when MCU chip is not worked, the output voltage of flyback topology constant voltage output unit is lower than the driving voltage of LED lamp string, when MCU chip operation, the current sense resistor that MCU chip is connected on dimmer switch pipe each road carries out analog voltage sampling, and described sampled voltage is processed, if there is the described sampled voltage of a paths of LEDs lamp string to be greater than preset value, the Voltage-output dutycycle of this paths of LEDs lamp string is exported in the adjustment of MCU chip, in order to maintain the constant current of each paths of LEDs lamp string, if there is the described sampled voltage of a paths of LEDs lamp string to be less than preset value, the MCU chip voltage of the LED lamp string of ceiling voltage as required, reduce MCU chip and export to the output voltage of flyback topology constant voltage output unit, increase the output voltage of flyback topology constant voltage output unit.
Described MCU chip comprises: A/D converter, CPU (central processing unit) and control module, A/D converter is issued CPU (central processing unit) after receiving and simulating signal being converted to digital signal after described sampled voltage, if finding that there is the described sampled voltage of a paths of LEDs lamp string, CPU (central processing unit) is greater than preset value, the Voltage-output dutycycle of this paths of LEDs lamp string is exported in control module adjustment, in order to maintain the constant current of each paths of LEDs lamp string, if finding that there is the described sampled voltage of a paths of LEDs lamp string, CPU (central processing unit) is less than preset value, the control module voltage of the LED lamp string of ceiling voltage as required, reduce MCU chip and export to the output voltage of flyback topology constant voltage output unit, increase the output voltage of flyback topology constant voltage output unit.
Described dimmer switch pipe is metal-oxide-semiconductor, and its source electrode is by resistance eutral grounding, and source electrode is also connected with the A/D converter in MCU chip by resistance simultaneously, and grid drives signal to be connected by resistance with MCU, and drain electrode connects with LED lamp series winding.
Between A/D converter input end in MCU chip and ground, be also connected with filter capacitor.
The present invention also provides a kind of driving method of the circuit that uses chip microcontroller multichannel backlight drive, and the method comprises:
The current sense resistor that MCU chip is connected on dimmer switch pipe each road carries out analog voltage sampling, and converts described analog voltage to digital signal;
Afterwards, described digital signal value and preset value are compared, if there is the described sampled voltage of a paths of LEDs lamp string to be greater than preset value, the Voltage-output dutycycle of this paths of LEDs lamp string is exported in the adjustment of MCU chip;
Compare with preset value, if there is the described sampled voltage of a paths of LEDs lamp string to be less than preset value, the MCU chip voltage of the LED lamp string of ceiling voltage as required, reduces MCU chip and exports to the output voltage of flyback topology constant voltage output unit.
Circuit and the driving method thereof of use chip microcontroller multichannel backlight drive of the present invention, by using flyback topology constant voltage output unit and MCU control module, make in the time that MCU chip is not worked, the output voltage of flyback topology constant voltage output unit is lower than the driving voltage of LED lamp string, in the time of MCU chip operation, the current sense resistor that MCU chip is connected on dimmer switch pipe each road carries out analog voltage sampling, and described sampled voltage is processed, if there is the described sampled voltage of a paths of LEDs lamp string to be greater than preset value, the Voltage-output dutycycle of this paths of LEDs lamp string is exported in the adjustment of MCU chip, in order to maintain the constant current of each paths of LEDs lamp string, if there is the described sampled voltage of a paths of LEDs lamp string to be less than preset value, the MCU chip voltage of the LED lamp string of ceiling voltage as required, reduce MCU chip and export to the output voltage of flyback topology constant voltage output unit, increase the output voltage of flyback topology constant voltage output unit.Foregoing circuit and driving method thereof, circuit structure is simple, flexible configuration, low cost of manufacture, safe.
Embodiment
Below, describe the present invention by reference to the accompanying drawings.
As shown in Figure 3, this example provides a kind of circuit that uses chip microcontroller multichannel backlight drive, this circuit comprises: flyback topology constant voltage output unit and MCU control module, wherein, MCU control module comprises: MCU chip, LED lamp string and with the LED lamp dimmer switch pipe connecing of contacting, dimmer switch pipe is connected with MCU chip by current sense resistor, and flyback topology output unit output voltage is to LED lamp string.
In the time that MCU chip is not worked, the output voltage of flyback topology constant voltage output unit is lower than the driving voltage of LED lamp string, in the time of MCU chip operation, the current sense resistor that MCU chip is connected on dimmer switch pipe each road carries out analog voltage sampling, and described sampled voltage is processed, if there is the described sampled voltage of a paths of LEDs lamp string to be greater than preset value, the Voltage-output dutycycle of this paths of LEDs lamp string is exported in the adjustment of MCU chip, in order to maintain the constant current of each paths of LEDs lamp string, if there is the described sampled voltage of a paths of LEDs lamp string to be less than preset value, the MCU chip voltage of the LED lamp string of ceiling voltage as required, reduce MCU chip and export to the output voltage of flyback topology constant voltage output unit, increase the output voltage of flyback topology constant voltage output unit.
Wherein, MCU(Micro Control Unit, micro-control unit), claim again single-chip microcomputer.
Described MCU chip comprises: A/D converter, CPU (central processing unit) and control module, A/D converter is issued CPU (central processing unit) after receiving and simulating signal being converted to digital signal after described sampled voltage, if finding that there is the described sampled voltage of a paths of LEDs lamp string, CPU (central processing unit) is greater than preset value, the Voltage-output dutycycle of this paths of LEDs lamp string is exported in control module adjustment, in order to maintain the constant current of each paths of LEDs lamp string, if finding that there is the described sampled voltage of a paths of LEDs lamp string, CPU (central processing unit) is less than preset value, the control module voltage of the LED lamp string of ceiling voltage as required, reduce MCU chip and export to the output voltage of flyback topology constant voltage output unit, increase the output voltage of flyback topology constant voltage output unit.
Dimmer switch pipe is metal-oxide-semiconductor, and its source electrode is by resistance eutral grounding, and source electrode is also connected with the A/D converter in MCU chip by resistance simultaneously, and grid drives signal to be connected by resistance with MCU, and drain electrode connects with LED lamp series winding.
Further, between A/D converter input end that can also be in MCU chip and ground, connect filter capacitor.
Particular circuit configurations, as shown in Figure 4, in the present embodiment, LED lamp string is 6 strings.The flyback topology constant voltage output unit as required LED lamp string of ceiling voltage is adjusted the size of output voltage; The constant current that MCU control module can be realized 6 string LED lamp strings drives, and reduces, because of the impact of the voltage difference between LED lamp string on dimmer switch pipe, in dimmer switch pipe Fig. 4, only to provide dimmer switch pipe Q1 and Q2.
1. the Voltage-output control procedure of flyback topology output unit is:
In the time that MCU chip is not worked, the output voltage of flyback topology output unit is determined by resistance R 2 and resistance R 3,1 pin reference voltage of TL431 stabilivolt is 2.495V, therefore the output voltage of the flyback topology of the potential-divider network control consisting of resistance R 2 and resistance R 3 is:
, this voltage should arrange the minimum voltage that is slightly less than LED lamp string, in the time that MCU chip is not worked, and can not driving LED lamp string when flyback topology output unit is exported this voltage.Only have when after MCU chip operation, its the 15th pin AD7 analog signal output pin output is less than the voltage of 2.495V, make resistance R 6 have electric current I 3 to flow through, thereby the output voltage of flyback topology output unit is raise, until this voltage meets the requirement of all lamp strings, the output voltage of flyback topology output unit is determined by the LED lamp string that needs maximum voltage.
Control procedure is as follows:
By the current equation that in the known Fig. 4 of Kirchhoff's current law (KCL), A is ordered be:
(formula 1),
Wherein:
(formula 2)
(formula 3)
(formula 4), wherein VAD7 is the analog voltage of the 15th pin AD7 pin output of MCU chip.
Formula 2,3,4 substitution formula 1 substitution numerical value are obtained:
(formula 5)
From formula 5, when in the magnitude of voltage of the VAD7 scope at 0V to 2.495V, its magnitude of voltage is less, the output voltage of flyback topology output unit is higher, therefore MCU chip is controlled the output voltage of flyback topology output unit by adjusting the Voltage-output of AD7 pin, until this voltage meets the requirement of all lamp strings.
2. MCU realizes multiple constant current and drives process:
In Fig. 4, only drawn two paths of LED backlight drive, this scheme can drive maximum LED lamp string number to be determined by selected MCU chip, therefore use MCU chip to drive and have larger dirigibility as constant current in the application of LED multi-path drive scheme.
This scheme becomes digital signal by the analog voltage using by mould/number conversion after the current sense resistor of LED lamp string series connection being sampled by the A/D pin of MCU chip, and the arithmetic core that meets at MCU chip is processed.If the digital-to-analog conversion of selected MCU chip is 10 precision, in the time that input voltage is 5V (the maximum input signal voltage of A/D is 5V), the voltage accuracy of the A/D pin of MCU chip is
, be 1V by programming AD0 pin to the reference voltage of AD5 pin, converting tens digit signal to is 208, the current value arranging is:
.If when AD0 pin has the value that is less than 208 after the voltage transitions of the sampling of AD5 pin becomes digital signal, by reducing the output voltage of AD7 pin, make the output voltage of flyback topology output unit increase; And be greater than 208 values after the voltage transitions of some pin sampling becomes digital signal, and the corresponding dutycycle that reduces this lamp string driving signal pins, the peak point current on Shi Gai road increases, and average current maintains in the error range of current value of setting.
The voltage of supposing LED lamp string 6 two ends is 55V, the voltage at LED lamp string 1 two ends is 53V, system is in the time just starting, the output voltage of flyback topology output unit only has 50.8V, therefore this voltage can not meet the requirement of LED lamp string 1 and LED lamp string 6, direct result is that the simulating signal that the A/D interface of MCU chip receives converts 208 values that digital signal is all less than program setting to, therefore according to system control principle, MCU chip is by reducing the output valve of analog voltage of AD7, make the output voltage of flyback topology output unit increase, until meet the requirement of all LED lamp strings.But, because there is certain voltage difference between each LED lamp string, if the both end voltage of LED lamp string 6 in example is than the large 2V of both end voltage of LED lamp string 1, therefore, therefore as shown in Figure 5, in the time that the output voltage of flyback topology output unit is 55V, flow through the just 100mA for setting of current value of LED lamp string 6, dutycycle is 100%; And LED lamp string 1 is because the output voltage 55V of flyback topology output unit is greater than the 53V of LED lamp string 1 needs own, so time flow through LED lamp string 1 current value increase, reach 125mA, the analog signal voltage of the feedback of the sampling resistor under this LED lamp string is greater than 1V, be greater than 208 by its numerical value after digital-to-analog conversion, the driving signal that now MCU chip is exported 80% dutycycle by PA0 pin can be controlled the ON time of LED lamp string 1, so time in one-period the average current of LED lamp string 1 be also 100mA, thereby realized the balance of brightness between LED lamp string.
In sum, described in the present embodiment, use the circuit of chip microcontroller multichannel backlight drive to have following advantage:
1) LED lamp string way is selected flexibly, to prepare as required required I/O mouth.
2) this circuit is directly controlled AC-DC part, can save the cost of DC-DC part.
3) constant current between LEDDeng Chuange road adopts the mode of adjusting dutycycle to realize, the peak point current of the LED lamp string that voltage is low is increased, thereby the voltage at LED lamp string two ends in the time of the conducting of MCU chip is increased, the pressure drop dropping on dimmer switch pipe is reduced, be of value to the temperature rise that reduces dimmer switch pipe.
As shown in Figure 6, the present embodiment also provides a kind of driving method that uses above-mentioned use chip microcontroller multichannel backlight drive circuit, and the method comprises:
The current sense resistor that MCU chip is connected on dimmer switch pipe each road carries out analog voltage sampling, and detects corresponding interface, for example analog voltage of ADX interface, and convert described analog voltage to digital signal; This X, which paths of LEDs lamp string representative is;
Afterwards, by described digital signal value and preset value, example 208 values described above compare, if there is the described sampled voltage of any paths of LEDs lamp string to be greater than preset value 208, the Voltage-output dutycycle of this paths of LEDs lamp string is exported in the adjustment of MCU chip;
Compare with preset value, if there is the described sampled voltage of any paths of LEDs lamp string to be less than preset value 208, the MCU chip voltage of the LED lamp string of ceiling voltage as required, reduces MCU chip and exports to the output voltage of flyback topology constant voltage output unit.
In sum, circuit and the driving method thereof of use chip microcontroller multichannel backlight drive of the present invention, by using flyback topology constant voltage output unit and MCU control module, make in the time that MCU chip is not worked, the output voltage of flyback topology constant voltage output unit is lower than the driving voltage of LED lamp string, in the time of MCU chip operation, the current sense resistor that MCU chip is connected on dimmer switch pipe each road carries out analog voltage sampling, and described sampled voltage is processed, if there is the described sampled voltage of a paths of LEDs lamp string to be greater than preset value, the Voltage-output dutycycle of this paths of LEDs lamp string is exported in the adjustment of MCU chip, in order to maintain the constant current of each paths of LEDs lamp string, if there is the described sampled voltage of a paths of LEDs lamp string to be less than preset value, the MCU chip voltage of the LED lamp string of ceiling voltage as required, reduce MCU chip and export to the output voltage of flyback topology constant voltage output unit, increase the output voltage of flyback topology constant voltage output unit.Foregoing circuit and driving method thereof, circuit structure is simple, flexible configuration, low cost of manufacture, safe.
The foregoing is only preferred embodiment of the present invention, in order to limit the present invention, within the spirit and principles in the present invention not all, any amendment of doing, be equal to replacement, improvement etc., within all should being included in protection scope of the present invention.