[0030] It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.
[0031] Reference figure 2 The present invention provides an embodiment of an LED backlight driving circuit 10. The LED backlight driving circuit 10 supplies power to the LED backlight module (not shown in the figure), which includes: a voltage stabilizing circuit 11, a first boosting circuit 12, a second boosting circuit 13, and a selection control circuit 14; the stabilizing circuit 11. Receive the input voltage, filter the input voltage, and output a regulated direct current; the first boost circuit 12 receives the regulated direct current, boosts it, and outputs it to the LED backlight module; the second boost The circuit 13, which receives the regulated DC power, boosts it, and outputs it to the LED backlight module; the selection control circuit 14 alternately selects the first boost circuit 12 and the second boost circuit 13, which is the LED backlight Module power supply.
[0032] The LED backlight driving circuit 10 of the present invention can solve the problems of increasing the duty cycle and reducing the efficiency (when the boost is higher) that may occur when a single existing Boost circuit is used for boosting; the LED backlight driving circuit 10, through The first step-up circuit 12 and the second step-up circuit 13 are provided to alternately supply power to the LED backlight module, so that the first step-up circuit 12 and the second step-up circuit 13 do not need to be provided with a capacitor for output voltage stabilization. When the voltage is increased to a higher level (such as 400V), the efficiency of the circuit will not be reduced, and the duty cycle will not increase, which has better practicability.
[0033] Reference image 3 In a specific example, the voltage stabilizing circuit 11 includes: two capacitors C2 and C3, respectively connected in parallel to the first boost circuit 12 and the second boost circuit 13; respectively, the first boost circuit 12 and The second booster circuit 13 provides a stable voltage. One ends of the two capacitors C2 and C3 are respectively connected to the first boost circuit 12 and the second boost circuit 13, and the other ends are connected to the ground.
[0034] In a specific example, the first boost circuit 12 includes: a first inductor L1, a second inductor L2, a diode D2 connected in series, and a MOS transistor whose drain is connected between the first inductor L1 and the second inductor L2 Q2: The gate of the MOS tube Q2 is connected to the selection control circuit, and the source is grounded; the above-mentioned MOS tube Q2 is a P-channel MOS tube. The second boost circuit 13 includes: a first inductor L3, a second inductor L4, a diode D1 connected in series in sequence, and a MOS transistor Q1 with a drain connected between the first inductor L3 and the second inductor L4; the MOS transistor The gate of Q1 is connected to the selection control circuit, and the source is grounded; the above-mentioned MOS tube Q1 is an N-channel MOS tube. Since the selection control circuit 14 controls the first boost module and the second boost module to boost alternately, it can be equivalent to the two sets of Boost circuits in the prior art for power supply, and the first boost module and the second boost module There is no need to set the output voltage stabilizing capacitor in the boost module. Therefore, corresponding to a set of Boost circuits in the prior art, the problem of boost efficiency (heating) is solved; compared to the combination of multiple sets of Boost circuits (reducing capacitance, PWM chip) 40 etc.), the cost is reduced.
[0035] In a specific example, the aforementioned selection control circuit 14 includes a push-pull circuit, a DC blocking circuit, and a PWM (Pulse Width Modulation, pulse width modulation technology) chip 40; the push-pull circuit is connected to the aforementioned MOS transistor Q1 and MOS transistor Q2, respectively. Connect, select the MOS transistor Q1 or the MOS transistor Q2 to be turned on; the DC blocking circuit is connected to the push-pull circuit to provide DC blocking voltage for the push-pull circuit; the PWM chip 40 is connected to the DC blocking circuit through the The DC blocking circuit and the push-pull circuit control the MOS transistor Q1 and the MOS transistor Q2 to be turned on alternately. The control of the PWM chip 40 also includes the on-time control of the MOS transistor Q1 and the MOS transistor Q2.
[0036] The above-mentioned push-pull circuit includes two triodes, namely a first triode Q3 and a second triode Q4; the emitters of the first triode Q3 and the second triode Q4 are connected, and the first triode The bases of the tube Q3 and the second triode Q4 are connected to the DC blocking circuit, the collector of the first triode Q3 is connected to the power source, and the collector of the second triode Q4 is grounded; The first transistor Q3 is of PNP type, and the second transistor Q4 is of NPN type. The aforementioned DC blocking circuit is a DC blocking capacitor C1.
[0037] The above-mentioned LED backlight driving circuit 10 will be described in detail below with reference to specific examples. The LED backlight driving circuit 10 is connected with an LED backlight module 20 and a constant current module 30 for constant current of the LED backlight module 20. (Reference image 3 )
[0038] The first step-up circuit 12 and the second step-up circuit 13 respectively form a set of coupled inductors through the first inductor L1 and the second inductor L2, and the third inductor L3 and the fourth inductor L4 form another set of coupled inductors; The turns ratio of the coupled inductor can increase the output voltage.
[0039] At the same time, the above-mentioned PWM chip (IC) 40 drives the N-channel MOS transistor Q1 and the P-channel MOS transistor Q2 through a DC blocking capacitor C1 and a set of PUSH-PULL circuits, so that the two MOS transistors can conduct at different times. And the on time of the two MOS tubes can be set.
[0040] When the PWM chip 40 outputs a high level, the first transistor Q3 of the push-pull circuit is turned on, and the MOS transistor Q1 in the second boost circuit 13 is turned on to charge the third inductor L3; at this time, the push-pull circuit The second transistor Q4 is turned off, the MOS transistor Q2 in the first boost circuit 12 is turned off, and the first inductor L1 and the second inductor L2 are discharged to supply power to the LED backlight module 20.
[0041] When the PWM chip 40 outputs a low level, the second transistor Q4 of the push-pull circuit is turned on, and the MOS transistor Q2 of the first boost circuit 12 is turned on, charging the first inductor L1; The first transistor Q3 is turned off, the MOS transistor Q1 in the second boost circuit 13 is turned off, and the third inductor L3 and the fourth inductor L4 are discharged to supply power to the LED backlight module 20.
[0042] The aforementioned PWM chip 40 can also sample the output voltage, compare the sampled output voltage with a reference voltage, and adjust the conduction time of the first boost circuit 12 and the second boost circuit 13 according to the comparison result to control The output voltage is constant; here is a closed-loop control. Among them, the PWM chip includes a pin (PIN) for feedback of the output voltage, and the output voltage is connected to the PIN through a resistor (not shown). The voltage of the PIN (that is, the output voltage) will be compared with the reference voltage inside the PWM chip. If the voltage of the PIN is higher than the reference voltage, the PWM chip reduces the duty cycle (DUTY, on-time) of the output by reducing the on-time /Cycle), reduce the output voltage, otherwise it will increase DUTY, increase the output voltage; in this way, the output voltage can be controlled to be constant.
[0043] The above-mentioned LED backlight driving circuit 10 realizes a high boost ratio through coupling inductors (L1 and L2 are coupled, L3 and L4 are coupled); the boost ratio can be determined according to the turns ratio of the two coupled inductors and the on-time of the boost circuit . Since the problem of circuit heating is solved, the LED backlight driving circuit 10 can have a higher boost ratio (for example, 24V input, 240V output, and a boost ratio of 10).
[0044] Since the LED backlight module 20 is controlled by a constant current, there are two LED arrangements: more strings and less parallel or less strings and more parallel; more strings and less parallel require high output voltage, and fewer strings and more parallel require balanced chips ( When the voltage rises to a higher position, more LEDs can be connected in series in the LED backlight module 20 to reduce the number of LEDs in parallel, so as to reduce the number of balance ICs (Balance IC). At the same time, since the LED backlight module 20 is under constant current control, the voltage difference between the different strings of LEDs connected in parallel is different, so increasing the number of LEDs in series can reduce the voltage difference of the LEDs (because the on-voltage is normally distributed). Conducive to optical design.
[0045] The above are only the preferred embodiments of the present invention, and do not limit the scope of the present invention. Any equivalent structure or equivalent process transformation made by using the content of the description and drawings of the present invention, or directly or indirectly applied to other related The technical field is similarly included in the scope of patent protection of the present invention.
